# Bias vs Variance

Part Of: Machine Learning sequence
Followup To: Regression vs Classification
Content Summary: 800 words, 8 min read

A Taxonomy of Models

Last time, we discussed how to create prediction machines. For example, given an animal’s height and weight, we might build a prediction machine to guess what kind of animal it is. While this sounds complicated, in this case prediction machines are simple region-color maps, like these:

These two classification models are both fairly accurate, but differ in their complexity.

But it’s important to acknowledge the possibility of erroneous-simple and erroneous-complex models. I like to think of models in terms of an accuracy-complexity quadrant.

This quadrant is not limited to classification. Regression models can also vary in their accuracy, and their complexity.

A couple brief caveats before we proceed.

• This quadrant concept is best understood as a two-dimensional continuum, rather than a four-category space. More on this later.
• Here “accuracy” tries to capture lay intuitions about prediction quality & performance. I’m not using it in the metric sense of “alternative to F1 score”.

Formalizing Complexity

Neural networks are often used as classification models against large numbers of images. The complexity of the models tends to correlate with the number of layers. For some models then, complexity is captured in the number of parameters.

While not used much in the industry, polynomial models are pedagogically useful examples of regression models. Here, the degree of the polynomial expresses the complexity of the model: a degree-eight polynomial has more “bumps” than a degree-two polynomial.

Consider, however, the difference between the following regression models

$y_A = 4x^4 + 0.0001x^3 + 0.0007x^2 + 2.1x + 7$
$y_B = 4x^4 + 2.1x + 7$

Model A uses five parameters; Model B uses three. But their predictions are, for all practical purposes, identical. Thus, the size of each parameter is also relevant to the question of complexity.

The above approaches rely on the model’s parameters (its “visceral organs”) to define complexity. But it is also possible to rely on the model’s outputs (its “behaviors”) to achieve the same task. Consider again the classification decision boundaries above. We can simply measure the spatial frequency (the “squiggliness” of the boundary) as another proxy towards complexity.

Here, then, are three possible criteria for complexity:

1. Number of parameters
2. Size of parameters
3. Spatial frequency of decision manifold

Thus, operationalizing the definition of “complexity” is surprisingly challenging. But there is another way to detect whether a model is too complex…

Simplicity as Generalizability

Recall our distinction between training and prediction:

We compute model performance on historical data. We can contrast this with model performance again future data.

Take a moment to digest this image. What is it telling you?

Model complexity is not merely aesthetically ugly. Rather, complexity is the enemy of generalization. Want to future-proof your model? Simplicity might help!

Underfitting vs Overfitting

There is another way of interpreting this tradeoff, that emphasizes the continuity of model complexity. Starting from a very simple model, increases in model complexity will improve both historical and future error. The best response to underfitting is increasing the expressivity of your model.

But at a certain point, your model will become too complex, and begin to overfit the data. At that point, your historical error will continue to decrease, but your future error will increase.

Data Partitioning: creating a Holdout Set

So you now appreciate the importance of striking a balance between accuracy and simplicity. That’s all very nice conceptually, but how might you go about building a well-balanced prediction machine?

The bias trade-off is only apparent when the machine is given new data!  “If only I had practiced against unseen test data earlier”, the statistician might say, “then I could have discovered how complex to make my model before it was too late”.

Read the above regret again. It is the germinating seed of a truly enormous idea.

Many decades ago, some creative mind took the above regret and sought to reform it: “What stops me from treating some of my old, pre-processed data as if it were new? Can I not hide data from myself?”

This approach, known as data partitioning, is now ubiquitous in the machine learning community.  Historical-Known data is the training set, Historical-Novel data is the test set, aka the holdout set.

How much data should we put in the holdout set? While the correct answer ultimately derives from the particular application domain, a typical rule of thumb:

• On small data (~100 thousand records), data are typically split to 80% train, 20% test
• On large data (~10 billion records), data are typically split to 95% train, 5% test

Next time, we will explore cross-validation (CV). Cross-validation is sometimes used instead of, and other times in addition to, data partitioning.

See you then!

# Why are humans ecologically dominant?

Part Of: Demystifying Culture sequence
Content Summary: 1100 words, 11 min read

Ecological Dominance

Compared to the erects, sapiens are uniquely ecologically dominant. The emergence of hunter-gatherers out of Africa 70,000 years ago caused:

• The extermination of hundreds of megafauna species (more than 90%)
• Dwarfing of the surviving species.
• A huge increase in the frequency and impact of fire (we used fire to reshape ecosystems to our liking)

12,000 years ago, we began domesticating animals and plants. The subsequent agricultural revolution unlocked powerful new ways to acquire energy, which in turn increased our species’ population density.

• 9000 BCE:   5 million people
•          1 CE:   300 million people
•   2100 CE:   11,000 million people

200 years ago, the industrial revolution was heralded by the discovery of energy transduction: that electricity can be used to run a vacuum, or freeze meat products.

These population explosion correlates with a hefty ecological footprint:

• We have altered more than one-third of the earth’s land surface.
• We have changed the flow of two-thirds of the earth’s rivers.
• We use 100 times more biomass than any large species that has ever lived.
• If you include our vast herds of domesticated animals, we account for more than 98% of terrestrial vertebrate biomass.

Three Kinds of Theories

As with any other species, the scientist must explain how ours has affected the ecosystem. We can do this by examining how our anatomies and psychologies differ from other animals, and then consider which of these human universals explain our ecological dominance.

Pound for pound, other primates are approximately twice as strong. We also lack the anatomical weaponry of our cousins; for example, our canines are much less dangerous.

So, strength cannot explain our dominance. Three other candidate theories tend to recur:

1. We are more intelligent and creative. Theories of this sort focus on e.g., the invention of Mode 3 stone tools.
2. We are more cooperative and prosocial. Theories of this sort focus on e.g., massively cooperative hunting expeditions.
3. We accumulate powerful cultural adaptations. Theories of this sort focus on e.g., how Inuit technology became uniquely adaptive for their environment.

Let’s take a closer look!

Intelligence-Based Theories

Is intellect the secret for our success? Consider the following theories:

First, generative linguists like Noam Chomsky argue that language is not about communication: recursion is an entirely different means of cognition; the root of our species’ creativity. To him, the language instinct (as a genetic package) appeared abruptly at 70 kya, and transformed the mind from a kluge of instincts to a mathematical, general-purpose processor. Language evolution is said to coincide with the explosion of technology called behavioral modernity.

Second, evolutionary psychologists like Leda Cosmides & John Tooby advocate the massive modularity hypothesis: the mind isn’t general purpose processor; it is instead more like a swiss army knife. We are not more intelligent because we have fewer instincts, but more. Specifically, we accrued hundreds of hunter-gatherer instincts in the intervening millenia and these instincts give us our characteristically human flexibility.

Third, social anthropologists like David Lewis-Williams argues that a change in consciousness made us more intelligent. We are the only species that has animistic spirituality, these are caused by numinous experiences. These altered states of consciousness were the byproducts of our consciousness machinery rearranging itself. Specifically, he invokes Dehaene’s theory that while all mammals experience primary consciousness, only sapiens have second-order consciousness (awareness of their own awareness). This was allegedly the event that caused fully modern language.

Sociality-Based Theories

Is sociality the secret for our success? Consider the following theories:

First, sociobiologists like Edward O Wilson thinks that the secret of our success is because of group selection: that vigorous between-group warfare created selective pressure for within-group cooperation. As our ethnic psychology (and specifically, ethnocentrism) became more pronounced, sapien tribes began behaving much like superorganisms. A useful analogy is eusocial insects like ants, who became are arguably even more ecologically dominant than humans.

Second, historians like Yuval Harari thinks that mythology (fictional orders) is the key ingredient enabling humans to act cooperatively. Political and economic phenomena don’t happen in a vacuum: they are caused by certain ideological commitments e.g., nationalism and the value of a currency. To change our myths is to refactor the social structure of our society.

Culture-Based Theories

Is culture the secret for our success? Consider the following theory:

Anthropologists like Richerson, Boyd and Henrich argue that cumulative cultural knowledge comprises a dual-inheritance system, and propose a theory of gene-culture coevolution. They are that an expanding collective mind gave individuals access to unparalleled know-how. This is turn emboldened our niche stealing proclivities: “like the spiders, hominins could trap, snare, or jet their prey; but the latter could also ambush, excavate, expose, entice, corral, hook, spear, preserve, or contain a steadily enlarging range of food types.” Socially-learned norms induce our cooperation, and socially-learned thinking tools explain our intelligence.

My Take

Contra Chomsky,

Contra Cosmides & Tooby:

• I agree wholeheartedly with the massive modularity hypothesis. It accords well with modern cognitive neuroscience.
• While selection endowed us with hunter-gatherer instincts (e.g., folk biology), I don’t think such instincts provide sufficient explanatory power.

Contra David Lewis-WIlliams:

• I need hard evidence showing that animals never hallucinate, before appropriating numinous experiences as a human universal.
• Global Workspace Theory (GWT) enjoys better empirical support than integrated information theory.
• I don’t understand the selective pressure or mechanistic implications for changes to our conscious machinery.

Contra sociality-first theories

• Group selection is still immersed in controversy, especially the free-rider problem.
• Why must myths be the causal first movers? Surely other factors matter more..

My own thinking most closely aligns with culture-based explanations of our ecological dominance. This sequence will try to explicate this culture-first view.

But at present, culture-first theories leaves several questions unanswered:

• What, specifically, is the behavioral and biological signature of a social norm? For now, appeals to norm psychology risk explaining too much.
• How did our species (and our species alone) become psychologically equipped to generate cumulative culture?
• If erectus was a cultural creature, why did the rate of technological innovation so dramatically change between erectus and sapiens?

Someday I hope to explore these questions too. Until then.

References

1. Tim Flannery. The Future Eaters
2. David Lewis-Williams. The Mind in The Cave.
3. Yuval Harari. Sapiens.
4. Henrich, The Secret of Our Success

# The Evolution of Faith

Part Of: Demystifying Culture sequence
Content Summary: 1200 words, 12 min read

Context

Recall that human beings have two different vehicles for learning:

• Individual Learning: using personal experiences to refine behavioral techniques, and build causal models of how the world works.
• Social Learning: using social interactions to learn what other people have learned.

Today, we will try to explain the following observations:

• This value typically cannot be articulated by practitioners.

Why should this be the case?

Example 1: Manioc Detoxification

Consider an example of food preparation, provided by Joseph Henrich:

In the Colombian Amazon, a starchy tuber called manioc has lots of nutritional value, but also releases hydrogen cyanide when consumed. If eaten unprocessed, manioc can cause chronic cyanide poisoning. Because it emerges only gradually after years of consuming manioc that tastes fine, chronic poisoning is particularly insidious, and has been linked to neurological problems, paralysis of the legs, thyroid problems, and immune suppression.

Indigenous Tukanoans use a multistep, multiday processing technique that involves scraping, grating, and finally washing the roots in order to separate the fiber, starch, and liquid. Once separated, the liquid is boiled into a beverage, but the fiber and starch must then sit for two more days, when they can then be baked and eaten. Chemical analyses confirm that each major step in the processing is necessary to remove cyanogenic content from the root. [5]

Yet consider the point of view of a woman learning such techniques. She may never have seen anyone get cyanide poisoning, because the techniques work. And she would be required to spend about four hours per day detoxifying manioc. [4]

Consider what might result if a self-reliant Tukanoan mother decided to drop seemingly unnecessary steps from the processing of her bitter manioc. She might critically examine the procedure handed down to her from earlier generations and conclude that the goal of the procedure is to remove the bitter taste. She would quickly find that with the much less labor-intensive process of boiling, she could remove the bitter taste. Only decades later her family would begin to develop the symptoms of chronic cyanide poisoning.

Here, the willingness of the mother to take on faith received cultural practices is the only thing preventing the early death of her family. Individual learning does not pay here; after all, it can take decades for the effects of the poison to manifest. Manioc processing is causally opaque.

The detoxification of dozens of other food products (corn, nardoo, etc) are similarly inscrutable. In fact, history is littered with examples of European explorers imperfectly copying indigenous food processing techniques, and meeting gruesome ends.

Example 2: Pregnancy Taboos

Another example, again from Henrich:

During pregnancy and breastfeeding, women on Fiji adhere to a series of food taboos that selectively excise the most toxic marine species from their diet. These large marine species, which include moray eels, barracuda, sharks, rock cod, and several large species of grouper, contribute substantially to the diet in these communities; but all are known in the medical literature to be associated with ciguatera poisoning.

This set of taboos represents a cultural adaptation that selectively targets the most toxic species in women’s usual diets, just when mothers and their offspring are most susceptible. [2] To explore how this cultural adaptation emerged, we studied both how women acquire these taboos and what kind of causal understandings they possess. Fijian women use cues of age, knowledge, and prestige to figure out from whom to learn their taboos. [3] Such selectivity alone is capable of generating an adaptive repertoire over generations, without anyone understanding anything.

We also looked for a shared underlying mental model of why one would not eat these marine species during pregnancy or breastfeeding: a causal model or set of reasoned principles. Unlike the highly consistent answers on what not to eat and when, women’s responses to our why questions were all over the map. Many women simply said they did not know and clearly thought it was an odd question. Others said it was “custom.” Some did suggest that the consumption of some of the species might result in harmful effects to the fetus, but what precisely would happen to the fetus varied greatly: many women explained that babies would be born with rough skin if sharks were eaten and smelly joints if morrays were eaten.

These answers are blatant rationalizations: “since I’m being asked for a reason, let me try to think one up now”.  The rationale for a taboo is not perceived by its adherents. This is yet another example of competence without comprehension.

A Theory of Overimitation

Human beings exhibit overimitation: a willingness to adopt complex practices even if many individual steps are inscrutable. Overimitation requires faith, defined here as a willingness to accept information in the absence of (or even contrasting with) your personal causal model.

We have replicated this phenomenon in the laboratory. First, present a puzzle box to a child, equipped with several switches, levers, and pulleys. Then have an adult teach the child how to open the box and get the treat inside. If the “solution” involves several useless procedures e.g., tapping the box with a stick three times, humans will imitate the entire procedure. In contrast, chimpanzees ignore the noise, and zoom in on the causally efficacious steps.

Why should chimpanzees outperform humans in this experiment? Chimpanzees don’t share our penchant for mimicry. Chimpanzees are not gullible by default. They must try to parse the relevant factors using the gray matter between their ears.

Humans fare poorly in such tests, because these opaque practices are in fact useless. But more often in our prehistory, inscrutable practices are nevertheless valuable. We are born to go with the flow.

In a species with cumulative culture, and only in such a species, faith in one’s cultural inheritance often yields greater survival and reproduction.

We humans do not spend much time inspecting the content of our cultural inheritance. We blindly copy it. How then can cultural practices be adaptive?

For the same reason that natural selection produces increasingly sophisticated body plans. Communities with effective cultural practices outcompete their neighbors.

Overimitation serves to bind cultural practices together into holistic traditions. This makes another analogy to natural selection apt:

• Genes don’t die, genomes die. Natural selection transmits an error signal for an entire genetic package.
• Memes don’t die, traditions die. Cultural selection transmits an error signal for an entire cultural package.

Just as genomes can host individual parasitic elements (e.g., transposons), so too cultural traditions can contain maladaptive practices (e.g., dangerous bodily modifications). As long as the entire cultural tradition is adaptive, dangerous ideas can persist undetected in a particular culture.

Does Reason Matter? Yes.

So far, this post has been descriptive. It tries to explain why sapiens are prone to overimitation, and why faith is an adaptation.

Yet individual learning matters. Without it, culture would replicate but not improve. Reason is the fuel of innovation. We pay attention to intelligent, innovative people because of another cultural adaptation: prestige.

Perhaps the powers of the lone intellect are less stupendous than you were brought up to believe.

But we need not be slaves to neither our cultural nor our genetic inheritance. We can do better.

Related Resources

1. Henrich (2016). The Secret Of Our Success.
2. Henrich & Henrich (2010). The evolution of cultural adaptations: Fijian food taboos protect against dangerous marine toxins
3. Henrich & Broesch (2011). On the nature of cultural transmission networks: evidence from Fijian villages for adaptive learning biases
4. Dufour (1984). The time and energy expenditure of indigenous women horticulturalists in the northwest Amazon.
5. Dufour (1994). Cassave in Amazonia: Lessons in utilization and safety from native peoples.

# [Excerpt] Jesus as Apocalyptic Prophet

Excerpt From: Blog Post
Content Summary: 1800 words, 9 min read

I agree with mainstream scholarship on the historical Jesus (e.g., E.P. Sanders, Geza Vermes, Bart Ehrman, Dale Allison, Paula Fredriksen, et al.) that Jesus was a failed apocalyptic prophet. Such a hypothesis, if true, would be a simple one that would make sense of a wide range of data, including the following twenty:

1. John the Baptist preached a message of repentance to escape the imminent judgment of the eschaton. Jesus was his baptized disciple, and thus accepted his message — and in fact preached basically the same message.
2. Jesus’ Son of Man passages are allusions to the son of man figure in Daniel 7:13-14 and Enoch ch 37-71 (both texts were widely discussed in first century Palestine). This figure was an end of the world arbiter of God’s justice, and Jesus kept preaching that he was on his way (e.g., “From now on, you will see the Son of Man sitting at the right hand of Power, and coming on the clouds of heaven.” Matt. 26:64).
3. The earliest canonical writing: Paul taught of an imminent eschaton, and it mirrors in wording the end-time passages in the synoptics (especially the so-called “Little Apocalypse” in Mark, and the subsequently-written parallels in Matthew and Luke).
4. Many passages depict Jesus predicting the end within his generation.
• “The time is fulfilled, and the kingdom of heaven is at hand. Repent and believe the good news” (Mark 1:15)
• “This generation will not pass away until all these things take place” (Mark 13:30)
• “You will not finish going through the cities of Israel until the Son of Man comes” (Matthew 10:23)
• “There are some of those who are standing here who will not taste death until they see the kingdom of God after it has come with power.” (Mark 9:1)
• “From now on, you shall see the Son of Man coming in the clouds” (Matt 26:64)
5. A sense of urgency permeates the gospels and the other NT writings. For example:
• The disciples must hurry to send the message to the cities of Israel before Daniel’s “Son of Man” comes
• Jesus’ statement that even burying one’s parents has a lower priority
• Paul telling the Corinthians not to change their current state, since it’s all about to end (e.g., don’t seek marriage, or to leave one’s slave condition, etc., since the end of all things is at hand)
6. Relatedly, Jesus and Paul taught a radical “interim ethic” (e.g., don’t divorce, radical forgiveness, don’t judge others, love one’s enemies, etc.). This makes sense if they believed that the eschaton would occur within their generation, and that all needed to repent and prepare for its arrival.
7. Jesus had his disciples leave everything and follow him around. This makes sense if Jesus believed that he and they were to be God’s final messengers before the eschaton.
8. Jesus gathered twelve disciples, which is the number of the twelve tribes of Israel. He also said they were to sit on twelve thrones and serve as judges of the twelve tribes of Israel. This reflects the common expectation that at the end of days, all twelve tribes would return to the land. The twelve are a symbolic representation of restored Israel.
9. There is a clear pattern of a successive watering down of Jesus’ prediction of the eschaton within the generation of his disciples, starting with Mark (widely believed among NT scholars to be the first gospel written), and continuing through the rest of the synoptic gospels. By the time we get to John, the last gospel written, the eschatological “kingdom of God” talk is dropped (except for one passage, and it no longer has clear eschatological connotations), along with the end-time predictions, and is replaced with “eternal life” talk. Further, the epistles presuppose that the early church thought Jesus really predicted the end within their lifetimes. Finally, this successive backpedaling continues beyond the NT writings and into those of the apocrypha and the early church leaders, even to the point where some writings attribute an anti-apocalyptic message to Jesus. All of these things make perfect sense if Jesus really did make such a prediction, and the church needed to reinterpret his message in light of the fact that his generation passed away, yet the eschaton never came.
10. Jesus’ base followers were all considered to represent the “bottom” of society in his day: the poor, sinners, prostitutes, outcasts, tax collectors, lepers, and the demon-possessed. This is perfectly in line with the standard apocalyptic doctrine of the reversal of fortunes when the kingdom of God comes: “the first shall be last, and the last shall be first”.
11. Jesus performed many exorcisms, which he claimed marked the inbreaking of the kingdom of God on Earth. They were thus signs of the imminent apocalypse. Satan and his minions were being cast out of power, and God’s power was taking its place.
12. Jesus’ trip to Jerusalem for the Passover Celebration, and his subsequent activities there, are best explained in terms of his apocalyptic message and his perceived role in proclaiming it. Jesus went to the temple during the Passover Festival, and spent many days teaching about his apocalyptic message of the imminent coming kingdom of God. The apocalyptic message included the idea that the temple in Jerusalem would also be destroyed.
13. Jesus caused a disturbance in the temple itself, which appears to have been a symbolic enactment of his apocalyptic teaching about the temple’s destruction.
14. Jesus’ betrayal by Judas Iscariot, and Jesus’ subsequent arrest, is best explained in terms of Judas’ betraying to the religious authorities (the Sadducees and the chief priests) Jesus’ teaching (to his inner circle of disciples) that he would be the King of the Jews in the coming Kingdom of God.
15. Jesus was executed on the charge of political sedition, due to his claim that he was the King of the Jews. His execution was therefore directly related to his apocalyptic message of the imminent coming of the kingdom of God.
16. The fact that not just all New Testament authors, but the early church as a whole, believed the end would occur in their generation makes perfect sense if Jesus really did make such claims.
17. The passages that attribute these predictions to Jesus and Paul satisfy the historical criteria of multiple attestation (and forms), embarrassment, earliest strata (Mark, Q, M, L, Paul’s earliest letters, the ancient “Maranatha” creed/hymn) etc., thus strongly indicating that these words go back to the lips of Jesus.
18. Jesus’ parables: virtually all explicitly or implicitly teach a message about an imminent eschaton.
19. Jesus’ “inversion” teachings (e.g., “The first shall be last, and the last shall be first”): a common theme among Jewish apocalypticists generally. The general message of apocalypticists is that those who are evil and defy God will not get away with it forever. The just are trampled, and the unjust prosper; thus, this situation needs to be inverted – as it will be when the “Son of Man” from the book of Daniel comes to exact God’s judgment at any moment.
20. The earliest Christians believed that Jesus’ putative resurrection was (to use Paul’s terminology) the “first fruits” of the general resurrection of the dead at the end of time. This is an agricultural metaphor. When farmers reaped and ate the first fruits of the harvest, they would then reap the full harvest the very next day — the “general” harvest was “imminent”, as it was “inaugurated” with the reaping of the first-fruits. Similarly, the earliest Christians believed that the final judgement and the general resurrection were imminent, given their belief that Jesus’ resurrection was itself the inaugurating event of the general resurrection and the end of all things. Thus, there is a continuity between the beliefs of the early Christians and the beliefs of many Jews of his time: Jesus’ resurrection was fundamentally construed in these eschatological terms

And so, no matter which way you slice it, the “statute of limitations” has run out on Jesus and his apostle’s claim for an imminent end, within a single generation.

It needs to be emphasized that this line of reasoning isn’t controversial among mainstream, middle-of-the-road NT critics. I’m not talking about a view held by the Jesus Seminar, or earlier “radical” form and redaction critics like Norman Perrin. Rather, I’m talking about the kinds of considerations that are largely accepted by moderates who are also committed Christians, such as Dale Allison and John P. Meier. Indeed, conservative scholars of the likes of none other than Ben Witherington and N.T. Wright largely admit this line of reasoning. Why are they still Christians, you ask? I’ll tell you: by giving unnatural, ad hoc explanations of the data. For example,

1. Meier gets around the problem by arguing that the false prediction passages are inauthentic (i.e., Jesus never said those things; the early church just put those words on the lips of Jesus, and they ended up in the gospels).
2. Witherington gets around the problem by saying that what Jesus really meant was that the imminent arrival of the eschatological kingdom might be at hand(!)
3. Wright gets around the problem by adopting the partial preterist line that the imminent end that Jesus predicted really did occur — it’s just that it was all fulfilled with the destruction of Jerusalem.
1. Oh, really? So are we also to think that since he’s already come again, he’s not coming back? Or perhaps there will be a third coming?
2. And why does Paul tell various communities very far outside of Israel about the same sorts of predictions of an imminent end that would affect them — one that, like the one Jesus talked about, involved judgement, destruction, and the gathering of all the elect?

Are you convinced by these responses? Me neither. And now you know why nobody outside of orthodox circles buys them, either.

To all of this, I say what should be obvious: you know, deep in your gut (don’t you?) that such responses are unnatural, ad hoc dodges of what we know to be the truth here: Jesus really did predict the end within the lifetime of his disciples, but he was simply wrong.

This isn’t about some remark Jesus said in passing.  It was his central message: “Repent, for the kingdom of heaven is at hand!”

Putting it all together, we get the following argument for Jesus as a failed apocalyptic prophet:

• Let H1 be the hypothesis that Jesus was a failed apocalyptic prophet of an imminent eschaton.
• Let H2 be the hypothesis that Jesus is the Son of God of orthodox Christianity.
• Let D1-20 be the data sketched above.

Then the argument can be expressed as follows:

1. H1 is a better explanation of D1-20 than H2.
2. If H1 is a better explanation of D1-20 than H2, then H1 is more probable than H2.
3. Therefore, H1 is more probable than H2.

# [Excerpt] The Sphex Within You

Excerpt From: Keith Stanovitch, Robot’s Rebellion
Content Summary: 400 words, 2 min read

Consider the behavior of the digger wasp, Sphex ichneumoneus.  The female Sphex does a host of amazing things in preparation for her eggs.

1. After digging a burrow, she flies off looking for a cricket.
2. When she finds one, she stings it in a way that paralyzes it but does not kill it.
3. She brings it back to the burrow and sets it just outside at the threshold
4. Then she goes inside to make sure things are safe inside the burrow.
5. If they are, she then goes back outside and drags in the paralyzed cricket.
6. She then lays her eggs inside the burrow, seals it up, and flies away.  When the eggs hatch, the wasp grubs feed off the paralyzed cricket which has not decayed because it was paralyzed rather than killed.

All of this seems to be a rather complex and impressive performance put on by the Sphex – a real exercise of animal intelligence.  It seems so, that is, until we learn that virtually every step of the wasp’s behavior was choreographed by rigid and inflexible preprogrammed responses to specific stimuli in the Sphex environment.

Consider, for example, the wasp’s pattern of putting the paralyzed cricket on the threshold of the burrow, checking the burrow, and then dragging the cricket inside.  Scientists have uncovered the rigidity of these behaviors by moving the cricket a few inches away from the threshold while the wasp is inside checking the burrow.  When she comes out, the wasp will not now drag the cricket in.  Instead, she will take the cricket to the threshold and go in again to check the burrow.  If the cricket is again moved an inch or so away from the threshold, the Sphex will again not drag the cricket inside, but will once more drag it to the threshold and for the third time go in to inspect the burrow.  Indeed, in one experiment where the investigators persisted, the wasp checked the burrow forty times and still not drag the cricket straight in.  These fixed action patterns dictated a certain sequence of behaviors triggered by a particular set of stimuli, and any deviation from this was not tolerated.

Ethologists often feel unnerved while observing insects and other lower animals: all that bustling activity, but there’s nobody home!

Let’s call this unnerving property sphexishness.  These simple, rigid routines that underpin the complexity of the surface behavior of simple creatures spawns in us a worrying thought:

What makes you sure you’re not sphexish – at least a little bit?

Modern theories of cognition all propose, in one way or another, that in fact we all are a little bit sphexish.  In fact, many of these theories, in emphasizing the pervasiveness of unconscious processing and the rarity and difficulty of analytic processing, are in effect proposing that our default mode of processing is sphexish.

# The Exodus of the Levites

Part Of: History sequence
Related To: Yahweh, god of metallurgy
Content Summary: 2200 words, 11 min read

Context

Last time, we explored the following:

• The Israelite origin story is largely a patriotic fiction.
• The Israelite people were indigenous Canaanites.
• The first Israelites worshiped the pantheon of El.
• The original Yahweh cult was a Shasu religion located in southern Edom
• Yahweh was first worshiped as a god of metallurgy
• The founder of Judaism, Moses, was said to be a Midianite
• Yahweh was introduced to Israel as a second tier deity (a member of El’s family)

But how was Yahwism transmitted to Israel? One obvious explanation involves trade; economic transactions often serve as a vehicle for transmission of religious ideas.

But then there’s the matter of the Exodus narrative. The absence of evidence for such a massive event gravitates against a massive exodus. But it is silent on the question of an exodus on a small scale.

There was no mass exodus. But I will argue there was a mini-exodus of a group of Levite priests from Egypt. The Biblical evidence suggests that Moses was a Midianite, and his encounter with Yahweh occurred in Midian.

Textual Evidence for a Levite Mini-Exodus

The Bible was written by four authors: J, E, P and D. Of these, E, P and D are traced to Levite priestly authors. There exist startling differences across Levite and non-Levite texts.

First, the two oldest texts in the Bible are the Song of the Sea, and the Song of Deborah. The Song of the Sea is a Levite text that does not mention Israel. The Song of Deborah, meanwhile, lists all ten tribes of Israel (Judah and Simeon were a separate community at this time and not part of Israel) but doesn’t mention Levi. Similarly, all twelve tribes are mentioned in the Blessings of Moses, but it is the only tribe associated with the exodus.

Second, only the Levite sources tell the entire story of the plagues and exodus from Egypt.  J, the non-Levite source, doesn’t tell it. If you read J, it jumps from Moses’ saying “Let my people go” in Exodus 5:1f to the people’s already having departed Egypt in Exodus 13:21.

Third, if the Levites brought Yahweh into Israel, they should be keen to describe the relationship between Yahweh and El. And only our Levite sources do this: J presumes the name is Yahweh from the beginning of her document.

Fourth, It is likewise the Levite sources that concentrate on the Tabernacle.  E mentions it a little; P treats it a lot. There is more about the Tabernacle than about anything else in the Torah.  But the non-Levite source J never mentions it at all.

Archaelogical Evidence

Egypt was known to host many Semitic peoples over the years. It is not unthinkable to imagine some small group escaping. The Shasu people were allowed by Mernepteh to bring their herds into Egyptian territory.

• Names of the Levites. Hophni, Hur, Phinehas, Merari, Pashhur and above all Moses are Egyptian names. No one else, in all the names mentioned in the Bible, has an Egyptian name. If Egyptian names were invented, why only attribute them to the Levites? Further, the story of Moses’ name suggests the Biblical redactors did not know these names were Egyptian).
• Cultural derivatives. There are strong parallels between the Levite priests’ description of the Ark and Egyptian barks. Likewise, the Seraphim that occupy the First Temple come from Egypt (the uraeus) IG.151. The serpent on Aaron’s staff mirrors Egyptian mythology. Professor Michael Homan showed that the Tabernacle has architectural parallels with the battle tent of Pharaoh Ramses II.
• Exodus 24:8 features Moses splashing blood on his followers in a ritual ceremony. This kind of blood covenant was unknown to Canaan, but common in pre-Islamic Arabia.
• Circumcision. Only texts written by Levites (11/11)  give the requirement to practice circumcision — which was a known practice in Egypt.  So Egyptian cultural influences are present, but only in the Levite texts!

The Levites came into contact with the Shasu cult, and brought Yahwism to Israel

We have seen that Yahweh was first worshiped as a god of metallurgy in Edom.

We have seen evidence that a mini-exodus of the Levites may be historical.

As far as I know, neither advocates of the Levite mini-exodus nor advocates of the Midianite-Kenite hypothesis see an obvious synergy between their theories:

The Levites left Egypt and encountered Yahweh in Midian.

We can see the overlap in these theories in Mount Sinai. Religious thinking in that era strongly associated gods with locations. Mount Sinai (aka Mount Horeb) was the house of Yahweh. This mountain was located in southern Edom, and the Levites regularly traveled to that location to worship him.

We can also see overlap in Moses’ home town. Moses was a Midianite:

Moses is described as having settled down with the Midianite people (the Shasu). His wife Zipporah and two sons were Midianite. What’s more: Moses’ father-in-law Jethro is called a priest. A priest of what god? Well, in Exodus 18:12, Jethro (and not Moses) is portrayed initiating a sacrifice to Yahweh. The Biblical editors seem uncomfortable with this tradition, for they later interjected a confession of faith on Jethro’s lips, which very much mirrors other such confessions. All of this suggests that Moses’ Midianite father-in-law was a priest of Yahweh. In fact, he seems to have spiritual authority over Moses in this passage.

The E source is replete with this kind of claim. We first meet Moses in Midian (no claims of him being born in Egypt, in this document). Moses’ response to Yahweh’s call, “Who am I that I should bring the Israelites out of Egypt?” would be a fair question for a man in Midian. E also claims he cannot go to Egypt because he is “heavy of tongue”. Traditionally interpreted as a speech defect, this phrase only occurs in one other place in the Hebrew Bible, where it means cannot speak the language. Finally, E also claims that the Midianites are direct descendents of Abraham.

While two Levite sources admit Moses’ Midianite connection, P actively tried to hide it. In the P source, has absolutely nothing about his ever being in Midian. Nothing about a Midianite wife, a priest father-in-law, nothing about his sons. Two books later, the P source injects a (blood-curdling) story designed to vilify the Midianites. Moses himself gives the order to kill all of the Midianite women. And this source does not include the little fact that Moses has a wife who happens to be a Midianite woman. The fact that the P source tries to deny the Midianite connection suggests the underlying claim is historical.

It is difficult to reverse-engineer the role of Moses

Three hypotheses seem possible:

1. Levites in Egypt, Moses in Midian. The Levites were enslaved Egyptians, who fled to the East, and fell under the influence of Moses, a Midianite Yahwist.
• Pro: Moses not speaking Egyptian language.
• Con: Hard to explain why Moses has an Egyptian name.
2. Levites in Egypt, Moses in Egypt. The “people” were enslaved in Egypt, and fled to the East, where their leader Moses converted to Yahwism.
• Pro: Moses has an Egyptian name
• Con: Hard to explain why Moses didn’t speak the Egyptian language.
3. Levites in Egypt, Moses in transit.
• Pro: explains both Moses’ Egyptian and Midianite stories.
• Con: Hard to explain why a Midianite would come to Egypt.

Of these hypotheses, the first seems most plausible to me. By the criterion of embarrassment, the evidence of Moses’ Midianite heritage strikes me as more persuasive than his alleged exploits in Egypt.

However, there seems to be inadequate evidence to fully resolve this question. Fortunately, the Levite-Kenite connection can survive this ambiguity. The key point is, once the Levites left Egypt, came into contact with the Shasu cult, and brought Yahwism to Israel.

The Levites “attached” themselves as priestly class

The Levites claim responsibility for the massacres in Genesis 34, Exodus 32:26-29, and Numbers 25:6-15 and Jacob’s blessing “Levi’s knives are vicious weapons. May I never enter their council. For in their anger they kill men, and on a whim they hamstring oxen. Their anger is cursed, for it is strong,and their fury, for it is cruel!” While the bloody purges specified in the conquest narrative are non-historical, they too speak towards the bloody zeal of the Levite people. All of this is to say: when they did arrive in Israel asking for refuge, they were not a people the Israelites could easily say no to.

In the book of Exodus, there are myriad references to “the people” and very few (retro-fitted) references to the Israelites. It is very plausible that “the people” referred exclusively to militant Levites. Deut 33:2-5 seems to support this distinction: “his people assembled with the tribes of Israel”.

On arrival, the Levites are not given territory. Instead, they are given a 10% tithe as priests. This fits into William Propp’s commentary on Exodus, which makes a strong case on the etymology of the very word “Levi” that its most probable meaning is an “attached person” in the sense of resident alien.

Over and over, the Levite sources command that one must not mistreat an alien. Why? “Because we were aliens in Egypt”. In the three Levite sources, the command to treat aliens fairly comes up 52 time! And how many times in the non-Levite source, J? None. Compared to legal texts of surrounding nations, this aspect is unique to the Israelite law code.

The Levites wrote the national history.

Those who accept that a mass exodus is non-historical still need to explain how the story of the Exodus made it into the Bible. But we are not being asked to explain how it was invented whole-cloth. Rather, we must explain why and how memory of the mini-exodus became stretched and aggrandized over time.

Why did the Levites invent the mass-exodus narrative?

1. Promoting worship of Yahweh. The Levites were convinced that Yahweh had saved them from Egypt. What better way to have Israel worship Yahweh, than create a new history?
2. Simple power politics. Political influence is easier to hold & retain if your group is the only “outsider”.
3. Political unification. Iron age Israel was theocratic. The priests and kings shared (and sometimes competed for) power. A common origin story is a powerful tool for unification and shared identity. Similarly, the demonization on lowland city states (cultural & ethic siblings) as “Canaanite” served to support campaigns against them.

How did they accomplish this? By the production and dissemination of an origin story.

While we are investigating the historicity of the Biblical narrative, we should also consider: why do these texts exist at all? The Hebrew Bible is humanity’s first attempt at prose, and of history. This intermingling of religion and history was unique to the ancient world. Instead of cyclic episodes of mythological combat, the Israelite religious imagination was fixated on events of their material past. Its structure is entirely unique, and cries out for an explanation. The Bible was written to create a written tradition (much more stable than oral traditions) of national identity.

In addition to violence, the Levites also had a reputation for teaching. We can see this in verses like Deuteronomy 6:20-23:

When your children ask you later on, “What are these laws that Yahweh commanded you?” you must say to them, “We were Pharaoh’s slaves in Egypt, but the Lord brought us out of Egypt in a powerful way. And he brought signs and great, devastating wonders on Egypt, on Pharaoh, and on his whole family before our very eyes. He delivered us from there so that he could give us the land he had promised our ancestors.

What specifically did the Levites fabricate?

They started with their own experience (an actual event), and added the following:

First, to make a mini-exodus massive, you need large numbers. You can actually “watch” the estimates grow as we move from earlier to later sources. J doesn’t mention numbers at all. E estimates a total of around 600,000, and P estimates of total of 600,000 fighting-age males (for a total of two million).

Second, the Exodus, without the conquest, would never have survived as a story. You need to explain how a nomadic nation came to reside in someone else’s territory. The conquest does this (and also stokes political sentiment of a later time period).

Why did the Israelites believe this story?

Don’t we all evaluate our personal origin stories with a bit too much credulity? Many Romans literally believed a wolf raised their patriarchs. Even in American culture, many people I’ve spoken with conceive of the Founding Fathers in mythic, rather than human, terms.

But why didn’t the first recipients of the mass exodus story reject it? Imagine the Levites waited ten or twenty generations before telling the story, and the mini-exodus narrative expansion happened only gradually. Israelites would only have distant inklings of the remembered past to go on. It is true that, for the exodus story to take root in early Israel it was necessary for it to pertain to the remembered past of settlers who did not emigrate from Egypt. And this is in fact the case. Egypt did control and oppress Canaan, during the mini-Exodus.

# The Cursorial Ape: a theory of human anatomy

Part Of: Anthropogeny sequence
Followup To
Content Summary: 2100 words, 21 min read

A Brief Review of Human Evolution

The most recent common ancestor of humans and chimpanzees lived 7 mya (million years ago). The very first unique hominin feature to evolve was bipedality, which was an adaptation for squat-feeding. The australopiths were bipedal apes. They could walk comfortably, but retained their adaptations for tree living as well. Dental morphology and microwear together suggest that australopiths acquired food from a new source: tubers (the underground storage organs of plants).

Climate change is responsible for the demise of the australopiths. Africa began drying out about 3 million years ago, making the woodlands a harsher and less productive place to live. Desertification would have reduced the wetlands where australopiths found fruits, seeds, and underwater roots. The descendents of Australopithecus had to adapt their diet.

The paranthropes adapted by promoting tubers from backup to primary food. These impressive creatures comprise a blend of human and cow-like features. In contrast, the habilines (e.g., Homo Habilis) took a different strategy: meat eating. These creatures had the same small bodies, but larger brains. Their hands show adaptations for flexibility, and their shoulders and elbows for throwing missiles. They began making stone tools (Mode 1 tools, the Oldowan industry). They presumably used these anatomical and cultural gifts to compete with other scavengers on the savannah (projectiles to repulse competitors, stone flakes to speedily butcher a carcass).

The habilines in turn gave rise to

• [1.9 mya] The erects (H erectus)  with near-modern anatomies.
• [0.9 mya] The archaics (H heidelbergensis) appear, who eventually give rise to the Neanderthals, Denisovans, and us.
• [0.3 mya] The moderns (H sapiens) emerge out of Africa, and completely conquer the globe.

A Closer Look

Yes, humans are apes. But why do we look so different from our closest living relative, the chimpanzee?

I have previously explained why we are bipedal (flexible waist, straight backs, walking on two feet).

But why do we have scent glands in our armpits? Fat in our asses? Such weird hair? Hairless skin with massive subcutaneous fat deposits?

Most of these changes were introduced with Homo Erectus:

Natural selection explains why bodies change. Anatomical innovations are selected when they enable more efficient exploitation of some particular niche.

So what ecological niche forged the modern human body?

Where Homo Erectus Evolved

The australopiths never made it beyond the southern margins of the Sahara. Because the adaptation of equatorial species inhibits their colonization of temperate regions, the successful emigration of the erects out of Africa strongly suggests that this was a northern, not a tropical species.

To evolve adaptations to dry, open country, the erects would have had to suffer a period of isolation from other hominins, in an appropriately discrete habitat. There were few, perhaps no, places in tropical or Southern Africa that could have provided such a combination. Comparing these constraints with the distribution of Homo Erectus fossils, comparative zoologist Jonathan Kingdon submits there the two most plausible contenders where the erects could have evolved are the Atlas Mountains, or Arabia.

Nasal evidence corroborates the hypothesis that they evolved in a desert environment. The entry to the primate nasal passage is flat, with straightforward air intake. Erect skulls show the first evidence of a protruding nose. A protruding nose forces the air at a “right angle” before entering the nasal cavity.

One of the responsibility of the nasal passage is to humidify the air before it is passed to the lungs. The increase in room and turbulence serves to amplify the humidification of inhaled air. Our noses are adaptations for desert living.

A New Thermoregulation System

There are two things unique to human skin:

• Functional hairlessness. We modern humans have hair, but it is so thin compared to chimpanzees that we are effectively hairless.
• Eccrine sweat glands. Our skin also contains a novel approach to sweat glands.

These two features are linked: we now know in exquisite molecular detail how incipient hair follicles are converted into eccrine glands (Lu et al 2016).

Other primates rely on oil-based apocrine sweat glands. The emergence of water-based eccrine glands in humans led to the “retirement” of apocrine glands in our lineage. The distribution of odor-producing apocrine glands was ultimately confined to our underarms and pubic regions.

Losing our hair had two important side-effects:

• Skin pigmentation. Fur protects against ultraviolet radiation. Without it, melanin was used as an alternate form of natural sunscreen.
• Why do otherwise-bald humans have hair at the tops of their heads? This is the location of maximal radiation.
• Why didn’t all humans remain dark-skinned? Melanin also inhibits the skin’s production of Vitamin D, and different locales have different radiation levels, requiring new tradeoffs to be struck.
• Subcutaneous fat. Ever seen a hairless chimpanzee? Human skin is much less wrinkled than other skin. Why? Even in non-obese people, humans store more of their body fat below the skin (versus in the abdomen, or between the muscles). This change has three complementary causes:
1. carnivores tend to store fat in this way,
2. mitigate the hernia risk associated with bipedality
3. replace the insulation services of fur, without interfering with sweat system.

We have reviewed four changes in human skin. Rather than a discrete event, these changes presumably evolved gradually, and in tandem.

Yes, but why are we hairless? There are many competing theories.

Jonathan Kingdon claims these skin adaptations arose late, as a parasite avoidance mechanism induced by increased population densities. Two rationales are provided: hair is a potent vector of infection, and the eccrine sweat system also has antibiotic properties.

This interpretation is challenged by genetic evidence that shows hominins were naked at least 1.2 mya, if not earlier (Rogers et al, 2004).

However, given the evidence suggesting Homo Erectus evolved in a desert climate, the most parsimonious theory seems to involve thermoregulation. We were exposed to less direct radiation given our upright posture; fur no longer served as critical of a role. But the overall climate was warm and dry,

Humans as Cursorial Species

A cursorial animal is one that is adapted for long-distance running, rather than animals with high acceleration over short distances; thus, a leopard is considered cursorial, while a cheetah is not. Other examples include wolves, horses, and ostriches.

Fit human amateurs can regularly run 10 kilometers, and longer distances such as marathons (42 kilometers) are achieved by tens of thousands of people each year. Such distances are unknown if not impossible for any other primate, but are comparable to those observed in specialized mammalian cursors on open habitats. African hunting dogs, for example, travel an average 10km per day.

Racing horses can gallop 10 kilometers at 9 meters per second. However, the sustainable galloping speeds in horses decline considerably for runs longer than 10-15 minutes. Well-conditioned human runners exceed the predicted preferred galloping speed for a 65-kg quadruped, and can even occasionally outrun horses over extremely long distances.

Thus, despite our embarrassingly slow sprinting speed, human beings can outcompete even cursorial animals at endurance running over large distances. How come? The answer has to do with our unique cooling system.

When other mammals trot, they cool themselves by panting. However, above certain speeds a quadruped transitions to a full gallop, which precludes panting. A horse can trot all day, but it cannot gallop continuously without overheating.

Human adaptations for running, and our unique eccrine sweat-based cooling system, meant that humans have a larger trot/gallop (jog/sprint) transition threshold. Our superior cooling technology is accentuated in high heat. We are literally the only mammal that can run a marathon in high heat.

Why are we Born to Run?

Our bodies are designed for endurance running. We are cursorial animals. But why?

To achieve this, hominids exploited a new form of predation called persistence hunting. The most successful persistence hunts will involve:

• Time: middle of the day (during peak heat)
• Target: big prey (overheats faster)

If you chase a big animal above its trot/gallop transition speed, the animal will easily distance itself and begin panting. But you can track the animal, and chase it again before it has the opportunity to fully recover. Repeat this process, and after 10-25 km you will successfully drive the prey into hyperthermia. This style of hunting has a remarkable 75% success rate. Modern hunters typically prefer to use the bow and arrow, but persistence hunting is still in their repertoire. Before the invention of projectile weapons some 71 kya, persistence hunting surely played a larger role.

We know that habilines ate meat (many bones show signs of their butchery). But they likely acquired meat by scavenging, as they were not particularly effective carnivores. Their adaptations for projectiles were presumably used to repulse competitors, and stone tools certainly helped speedily butcher a carcass.

Of the dozens of running adaptations in our Homo Erectus, a substantial fraction already exist in habilines. Presumably the re-invention of our skin had begun too. These processes presumably began for simple reasons (it pays to move quickly, and have less fur, in the savannahs that emerged 3 mya).

Persistence hunting completely changed the game. Adaptations for running brought steep rewards. In a typical persistence hunt, the hunter averages an energy expenditure of 850 Kcal; they energy gains from big game is multiple times larger. Compare the calorie budget for a modern-day hunter-gatherer with that of chimps: in our prime, we produce twice as many calories as we consume!

Life is fundamentally about getting energy to make more life.

Persistence hunting was the turning-point in human evolution. Our species began winning, in terms of our reliably acquiring surplus energy. This surplus was the reason why our lineage could “afford” bigger brains, taller bodies, more frequent births, and longer childhood. All of these characteristics have improved gradually & continuously since the erects emerged.

We have looked at the reasons behind our running. What does anatomy tell us?

First, let’s compare the physics of walking vs running:

• Walking is an inverted pendulum mechanism.  Our feet and our hips alternate as the center of rotation.
• Running is a mass-spring mechanism. Ligaments transfer foot-strike kinetic energy into tendons, which is released as we bounce onward.

Walking doesn’t require springs – but running does. And the bodies of erects have two new ligaments that serve precisely this purpose:

• The Achilles’ tendon stores and releases 35% of energy expended while running (but not walking). In chimps, this tendon is 1cm long. In erects, it is 10cm and much thicker.
• The dome-shaped arch of the foot is another spring, which lowers the cost of running by 17%.

During bipedal running the risk of falling and sprained ankles is high, which in the ancestral environment had adaptive consequences. Thus, the human body also developed many stabilization techniques:

• Gluteus maximus. Barely active during walking, this muscle contracts forcefully during running to prevent the trunk from toppling forward.
• Various head stabilization devices. Promotes vision continuity and protects the brain (watch a runner with a ponytail sometime).
• Enlarged semicircular canals (balance organs) in inner ear, which can be seen by measuring certain dimensions of fossilized skulls.

I have listed five features of our anatomy that relate to endurance running. Lieberman et al (2006) list twenty:

As you can see, not all of these running adaptations emerged with Homo Erectus. Homo Habilis already shows adaptations for running. It would not surprise me in the slightest if that species also saw the beginnings of our skin trajectory.

Adaptations for running came at a price. We have lost our ability to climb trees. We are the first primate to lose this ability.

Takeaways

Why do humans look so different from our closest living relative, the chimpanzee?

Why do we have scent glands in our armpits? Fat in our asses? Such weird hair? Hairless skin with massive subcutaneous fat deposits?

Animal body plans are designed to excel in a particular niche. Our bodies are designed for persistence hunting. Compared to other primates, our anatomies optimize for thermoregulation, efficient energy transfer, and stabilization during running.

Chimpanzees don’t need to exercise to stay fit. We do. Our health sees dramatic benefits from aerobic exercise, especially running.

References

• Bramble & Lieberman (2004). Endurance running and the evolution of Homo
• Lieberman et al (2006). The human gluteus maximus and its role in running
• Lu et al (2016). Spatiotemporal antagonism in mesenchymal-epithelial signaling in sweat versus hair fate decision.
• Rogers et al (2004). Genetic Variation at the MCiR Locus and the Time since Loss of Human Body Hair

# [Excerpt] How Language Evolved

Part Of: Language sequence
Excerpt From: (Johansson 2011) Constraining the Time When Language Evolved
Content Summary: 1600 words, 16 min read

The evolution of language had to involve at least a new ability to map concepts to sounds and gestures and to use these communicatively. But language actually consists of a good deal more than this: First, there is phonological structure—the systematized organization of sounds (or, in sign languages, gestures). Second is morphology—the internal structure of words, such that the word procedural can be seen as built from proceed plus -ure to form procedure, plus -al to form procedural: [[[proceed] [-ure]] [-al]]. Third is syntax, the organization of words into phrases and sentences.

One way to form plausible hypotheses about evolution is through reverse engineering: asking what components could have been useful in the absence of others. A primitive system for communicating thoughts via sound or gestures is useful without phonology, morphology, or syntax. The latter components can improve an existing communication system, but they are useless on their own. So if the components of language evolved in some order, it makes sense that the connection between phonetics and meaning came first, followed by these further refinements.

A system with a linear grammar would have words— that is, stored pairings between a phonological form and a piece of conceptual structure. The linear order of words in an utterance would be specified by phonetics, not by syntax. The individual words would map to meanings, but beyond linear order, there would be no further structure—no syntactic phrases that combine words and no morphological structure inside words (such as in the word procedural).

Indeed, we can find evidence for linear grammar in many different contexts.

1. As the early stages of contact languages, pidgins are often described as having no subordination, little or no morphology, no grammatical words like the, and unstable word order governed primarily by semantic principles like agent before action. If the context permits, the characters in the action can be left unexpressed. For instance, if the context had already brought the boy to attention, the speaker might just say girl kiss, which in English would require a pronoun—The girl kissed him. From the perspective of linear grammar, we can ask: Is there any evidence that pidgins have parts of speech like nouns and verbs, independently from the semantic distinction between individuals and actions? Indeed, there is no evidence for syntactic phrases, beyond semantic cohesion. Pidgin grammars are a good candidate for real-world examples of our hypothesized linear grammar.
2. For a second case, involving late second language acquisition, Wolfgang Klein and Clive Perdue did a multilanguage longitudinal study of immigrants learning various second languages all over Europe. They found that all speakers achieved a stage of semiproficiency that they called the Basic Variety. Many speakers went on to improve on the Basic Variety, but others did not. At this stage, there is no inflectional morphology or sentential subordination, and known characters are freely omitted. Instead, there are simple, semantically based principles of word order including, for instance, agent before action.
3. A third case is home signs, the languages invented by deaf children who have no exposure to a signed language. Susan Goldin-Meadow has shown that they have at most rudimentary morphology; they also freely omit known characters. In our analysis, home signs only have a semantic distinction of object versus action, not a syntactic distinction of noun versus verb. Word order is probabilistic and is based, if anything, on semantic roles. Homesigners do produce some sentences with multiple verbs, which Goldin-Meadow describes as embedding. We think these are rudimentary serial verb or serial action-word constructions, without embedding, sort of like the compound verb in English expressions such as He came running. So this looks like a linear grammar with possibly a bit of morphology.
4. Another case is village sign languages, which develop in isolated communities with a significant occurrence of hereditary deafness. A well-known example is Central Taurus Sign Language (CTSL), spoken in two remote villages in the mountains of Turkey. CTSL has some minimal morphology, mostly confined to younger speakers. But there is little or no evidence for syntactic structure. In sentences involving one character, the word order is normally agent + action, and two-character sentences are normally (optional) agent + patient + action: girl ball roll. But if a sentence involves two animate characters, so that semantics alone cannot resolve the potential ambiguity, word order is not very reliable. For instance, girl boy hit is a bit vague about whether the girl hit the boy or vice versa, requiring a huge reliance on pragmatics, common knowledge, and context. In fact, there is a strong tendency to mention only one animate character per predicate, so speakers sometimes clarify by saying things like Girl hit, boy get-hit. So CTSL looks like a linear grammar, augmented by a small amount of morphology. Similar results have been obtained in Al-Sayyid Bedouin Sign Language (ABSL) and the earlier stages of Nicaraguan Sign Language.
5. These less complex systems are not confined to emerging languages; they also play a role in language processing. Townsend and Bever (2001) discuss what they call semantically based interpretive strategies that influence language comprehension. In particular, hearers tend to rely in part on semantically based principles of word order such as agent precedes action, which is why (in our account) speakers have more difficulty with constructions such as reversible passives and object relatives, in which the agent does not precede the action. Similarly, Ferreira and Patson (2007) discuss good enough parsing, in which listeners apparently rely on linear order and semantic plausibility rather than syntactic structure. It is well known that we see similar though amplified symptoms in language comprehension by agrammatic aphasics. Finally, Van der Lely and Pinker (2014) argue that a particular population of children with specific language impairment behave as though they are processing language through something like a linear grammar. The literature frequently describes these so-called heuristics as something separate from language. But they are still mappings between phonetics and meaning—just simpler ones.
6. We have also encountered a full-blown language whose grammar appears to be close to a linear grammar: Riau Indonesian, a vernacular with several million speakers, described by Gil (2005, 2009). Gil argues that this language has no syntactic parts of speech and no inflectional morphology such as tense, plural, or agreement. Known characters in the discourse are freely omitted. Messages that English expresses with syntactic subordination are expressed in Riau paratactically, with utterances like girl love, kiss boy. The word order is quite free, but agents tend to precede actions, and actions tend to precede patients. This collection of symptoms again looks very much like a linear grammar. Hence, this is a language virtually all of whose grammar is syntactically simple in our sense. Similar results obtain for the Piraha language, whose non-recursivity is well explained by the linear grammar theory as well.
7. Another kind of linear grammar—that is, a system that relies on the linear order of the semantic roles being expressed to form conceptual relations—surfaces when people are asked to express actions or situations in a nonlinguistic task, such as in gesture or act-out tasks. Overall, there is a vast preference to gesture, or act out, the agent first (e.g., girl), and then the patient (e.g., boy). The action is usually expressed last (kiss), but when there is a potential ambiguity, people like to avoid it by expressing the action in the middle, between the agent and patient. Crucially, the ordering preferences in these tasks are remarkably stable, independently of the ordering preferences in test subjects’ native language. That seems to indicate that the capacity to map certain semantic notions to certain linear orders is at least partly independent from language itself.
8. As a final case, traces of something like linear grammar lurk within the grammar of English! Perhaps the most prominent case is compounding, in which two words are stuck together to form a composite word. The constituents may be any part of speech: not just pairs of nouns, as in kitchen table, but also longbow, undercurrent, castoff, overkill, speakeasy, and hearsay. The meaning of the composite usually includes the meanings of the constituents, but the relation between them is determined pragmatically. Consider examples like these:
• collar size = size of collar
• dog catcher = person who catches dogs
• nail file = something with which one files nails
• beef stew = stew made out of beef
• bike helmet = helmet that one wears while riding a bike
• bird brain = person whose brain is similar to that of a bird

The second noun usually determines what kind of object the compound denotes; for instance, beef stew is a kind of stew, whereas stew beef is a kind of beef. But this can be determined solely from the linear order of the nouns and needs no further syntax.

To sum up, remarkably similar grammatical symptoms turn up in a wide range of different scenarios. This suggests to us that linear grammar is a robust phenomenon, entrenched in modern human brains. It provides a scaffolding on top of which fully syntactic languages can develop, either in an individual, as in the case of the Basic Variety, or in a community, as in the case of pidgins and emerging sign languages. Furthermore, it provides a sort of safety net when syntactic grammar is damaged, as we have seen with aphasia and specific language impairment. We have also seen that it is possible to express a great deal even without syntax, for example in Riau Indonesian—though having syntax gives speakers more sophisticated tools for expressing themselves.

# [Excerpt] When Language Evolved

Part Of: Language sequence
Excerpt From: (Johansson 2011) Constraining the Time When Language Evolved
Content Summary: 900 words, 9 min read

Speech is not impossible with an ape vocal tract, but merely less expressive, with fewer vowels available. Furthermore, the vocal tract in living mammals is quite flexible, and a resting position different from the human configuration does not preclude a dynamically lowered larynx, giving near-human vocal capabilities, during vocalizations.

Adaptations for speech can be found in our speech organs, hearing organs, the neural connections between these organs, as well as the genes controlling their development.

• Speech organs. The shape of the human vocal tract, notably the permanently lowered larynx is very likely a speech adaptation, even though some other mammals, such as big cats, also possess a lowered larynx. The vocal tract itself is all soft tissue and does not fossilize, but its shape is connected with the shape of the surrounding bones, the skull base and the hyoid. Already Homo erectus had a near-modern skull base, but the significance of this is unclear, and other factors than vocal tract configuration, notably brain size and face size, strongly affect skull base shape. Hyoid bones are very rare as fossils, as they are not attached to the rest of the skeleton, but one Neanderthal hyoid has been found, as well as two hyoids from Homo heidelbergensis, all very similar to the hyoid of modern Homo sapiens, leading to the conclusion that Neanderthals had a vocal tract adequate for speech. The hyoid of Australopithecus afarensis, on the other hand, is more chimpanzee-like in its morphology, and the vocal tract that reconstruct for Australopithecus is basically apelike.
• Hearing organs. Some fine-tuning appears to have taken place during human evolution to optimize speech perception, notably our improved perception of sounds in the 2-4 kHz range. The sensitivity of ape ears has a minimum in this range, but human ears do not, mainly due to minor changes in the ear ossicles, the tiny bones that conduct sound from the eardrum to the inner ear. This difference is very likely an adaptation to speech perception, as key features of some speech sounds are in this region. The adaptation interpretation is strengthened by the discovery that a middle-ear structural gene has been the subject of strong natural selection in the human lineage These changes in the ossicles were present already in the 400,000-year-old fossils from Spain, well before the advent of modern Homo sapiens. These fossils are most likely Homo heidelbergensis. In the Middle East, ear ossicles have been found both from Neanderthals and from early Homo Sapiens, likewise with no meaningful differences from modern humans.
• Lateralization. There is no clearcut increase in general lateralization of the brain in human evolution — ape brains are not symmetric — and fossils are rarely undamaged and undistorted enough to be informative in this respect. But when tools become common, handedness can be inferred from asymmetries in the knapping process, the usewear damage on tools, and also in tooth wear patterns, which may provide circumstantial evidence of lateralization, and possibly language. Among apes there may be marginally significant handedness, but nothing like the strong population-level dominance of right-handers that we find in all human populations. Evidence for a human handedness pattern is clear among Neanderthals and their predecessors in Europe, as far back as 500 kya, and some indications go back as far as 1 mya. To what extent conclusions can be drawn from handedness to lateralization for linguistic purposes is, however, unclear.
• Neural connections. Where nerves pass through bone, a hole is left that can be seen in well-preserved fossils. Such nerve canals provide a rough estimate of the size of the nerve that passed through them. A thicker nerve means more neurons, and presumably improved sensitivity and control. The hypoglossal canal, leading to the tongue, has been invoked in this context, but broader comparative samples have shown that it is not useful as an indicator of speech. A better case can be made for the nerves to the thorax, presumably for breathing control. Both modern humans and Neanderthals have wide canals here, whereas Homo erectus has the narrow canals typical of other apes, indicating that the canals expanded somewhere between 0.5 and 1.5 million years ago.
• FOXP2. When mutations in the gene FOXP2 were associated with specific language impairment, and it was shown that the gene had changed along the human lineage, it was heralded as a “language gene”. But intensive research has revealed a more complex story, with FOXP2 controlling synaptic plasticity in the basal ganglia rather than language per se, and playing a role in vocalizations and vocal learning in a wide variety of species, from bats to songbirds. Nevertheless, the changes in FOXP2 in the human lineage quite likely are connected with some aspect of language, even if the connection is not as direct as early reports claimed. Relevant for the timing of the emergence of human language is that the derived human form of FOXP2 was shared with Neanderthals, and that the selective sweep driving that form to fixation may have taken place more than a million years ago, well before the split between Homo Sapiens and Neanderthals.

No single one of these indications is compelling on its own, but their consilience strengthens the case for some form of speech adaptations in Homo Heidelbergensis.

As the speech optimization, with its accompanying costs, would not occur without strong selective pressure for complex vocalizations, presumably verbal communication, this implies that Homo erectus already possessed non-trivial language abilities. While Homo erectus did not possess our species’ ability for ratcheting (cumulative) culture, it did exhibit art and sufficient skills to construct watercraft.