[Excerpt] Language vs Communication

Part Of: Language sequence.
Excerpt From: Tecumseh Fitch, The Evolution of Language
Content Summary: 800 words, 4 min read

What kind of sound does a dog make? That depends on which language you speak. Dogs are said to go ouah ouah in French, but ruff or woof in English. 

Crucially, however, the sounds that the dogs themselves make do not vary in this way. Dogs growl, whine, bark, howl and pant in the same way all over the world. This is because such sounds are part of the innate behavioral repertoire that every dog is born with. This basic vocal repertoire will be present even in a deaf and blind dog. This is not, of course, to say that dog sounds do not vary: they do. You may be able to recognize the bark of your own dog, as an individual, and different dog breed produce recognizably different vocalizations. But such differences are not learned; they are the inevitable byproducts of the fact that individuals vary, and  differences at the morphological, neural or “personality” level will have an influence on the sounds an individual makes. Dogs do not learn how to bark or growl, cats do not learn how to meow, and cows do not learn their individual “moos”. Such calls constitute an innate call system. By “innate” in this context, I simply mean “reliably developing without acoustic input from others” or canalized. For example, in experiments where young squirrel monkeys were raised by muted mothers, and never heard conspecific vocalizations, they nevertheless produced the full range of calls. 

The same regularity applies to important aspects of human communication. A smile is a smile all over the world, and a frown or grimace of disgust indicates displeasure everywhere. Not only are many facial expressions equivalent in all humans, but their interpretation is as well. Many vocal expressions are equally universal. Such vocalizations as laughter, sobbing, screaming, and groans of pain or pleasure are just as innately determined as the facial expressions that normally accompany them. Babies born both deaf and blind, unable to perceive either facial or vocal signals in their environment, nonetheless smile, laugh , frown, and cry normally. Again, just as for dog barking, individuals vary, and you may well recognize the laugh of a particular friend echoing above the noise in a crowded room. And we have some volitional control over our laughter: we can (usually) inhibit socially inappropriate laughter. These vocalizations form an innate human call system. Just like other animals, we have a species-specific, innate set of vocalizations, biologically associated with particular emotional and referential states. In contrast, we must learn the words or signs of language. 

This difference between human innate calls, like laughter and crying, and learned vocalizations, like speech and song, is fundamental (even down to the level of neural circuitry). An anencephalic human baby (entirely lacking a forebrain) still produces normal crying behavior but will never learn to speak or sing. In aphasia, speech is often lost while laughter and crying remain normal. Innate human calls provide an intuitive framework for understanding a core distinction between language and most animal signals, which are more like the laughs and cries of our own species than like speech. Laughs and cries are unlearned signals with meanings tied to important biological functions. To accept this fact is not to deny their communicative power. Innate calls can be very expressive and rich – indeed their affective power may be directly correlated with their unlearned nature. The “meaning” of a laugh can range from good-natural conviviality to scornful, derisive exclusion, just as a cat’s meow might “mean” she wants to go out, she wants food, or she wants to be petted. Insightful observers of animals and man have recognized these fundamental facts for many years. 

Obviously, signals of emotion and signals of linguistic meaning are not always neatly separable. In vocal prosodic cues, facial expressions, and gestures, our linguistic utterances are typically accompanied by “non-verbal” cues to how we feel about what we are saying. One signal typically carries both semantic information intelligible only to those who know the language, and a more basic set of information that can be understood by any human being or even other animals. Non-verbal expressive cues are invaluable to the child learning language, helping to coordinate joint attention and disambiguate the message and context. They also make spoken utterances more expressive than a written transcription alone. Other than the exclamation mark or emoticons, our tools to transcribe the expressive component are limited, but the ease and eagerness with which humans read illustrates that we can nonetheless understand language without this expressive component. This too, reinforces the value of a distinction between two parallel, complementary systems. 

As we discuss other animals’ communication systems, I invite the reader to compare these systems not only to language exchanges, but also to the last time you had a good laugh with a group of friends, and the warm feeling that goes along with it, or the sympathetic emotions summoned by seeing someone else cry, scream, or groan in pain. The question we must ask – “is this call type more like human laughter and crying, or more like speech or song?”. I will shortly argue that all non-human communication systems fall in the former category. 

Advertisements

Intro to Continental Drift

Part Of: Biology sequence
Content Summary: 1500 words, 15 min read

Continental Drift

Every school child recognizes that the shape of Africa and South America “match” with one another, like puzzle pieces. Trained geologist Alfred Wegener went further, and showed that not only the shape of the continents match, but a beach in South America often was more similar to its “counterpart” in Africa than it was to adjacent beaches along the coastline. On the basis of such data, he proposed continental drift. Africa and South America had once been neighbors, but spread apart over the course of Earth’s history. 

The theory of continental drift was initially controversial. The evidence of continental drift was there, yet geologists were unconvinced because they could not conceive of a mechanism: a physical process that might cause entire continents to move. The Expanding Earth hypothesis held that continental drift was an artifact of an expanding earth, with oceans “filling in the gaps” between the continents – but these conjectures were never formalized, nor did they receive experimental support. Eventually, however, powerful evidence led tectonic theory to emerge as the mechanism powering continental drift. 

Let’s turn our attention to tectonic theory.

Tectonic Theory

The very first evidence of tectonic theory came from expeditions to map the ocean floor. These revealed enormous mountain ranges that ran down precisely the middle of the Atlantic Ocean (among other places). Those mountain ranges were later discovered to be volcanically active. Deep trenches were also discovered around this time.

It was at this time realized that the volcanoes and trenches comprised a kind of conveyor belt system, with two complementary mechanisms for creating and retiring crust. Just as wooden blocks are pulled apart when placed in boiling water, continents are pulled apart by convection currents generated by the Earth’s core.

Our ability to use seismographs to record earthquakes was also maturing. You may have heard of the Ring of Fire; a shape along the edge of the Pacific Ocean with higher susceptibility to Earthquakes (I’m looking at you, San Francisco). If you look at a more complete distribution of earthquakes, you can begin to see shapes emerging. 

These tiles are tectonic plates. Here is a higher resolution image of plate boundaries. 

Tectonic plates are not hypotheses; they are physical objects with a history. A good way to appreciate this is by understanding that we can use earthquake measurement instruments to see into the Earth’s interior, in a process not unlike echolocation. Such techniques have been used to figure out the diameter of Earth’s core. They have also revealed fully submerged tectonic plates. These include the Farallon Plate underneath North America, which has not yet been fully reabsorbed by the surrounding mantle.

When rocks are created, they are hot enough to receive an imprint of the Earth’s magnetic field. During WW2, submarines noticed the seafloor was striped: at one location, the magnetic field was pointed North; move a few kilometers west, and the field pointed South. Why the stripes? Separately, evidence emerged for geomagnetic reversals: during the last 83 million years, the Earth’s magnetic field has reversed 183 times. Continental drift and geomagnetic reversals explain the magnetic stripes.

Volcanos, Mountains, and Cratons

Volcanoes promote seafloor spreading. But not all volcanoes exist at crust boundaries. Consider Hawaii. The fifteen volcanoes that make up the eight islands of Hawaii are the youngest in a chain of more than 129 volcanoes in the Hawaiian-Emperor seamount chain. Note the “V” shaped pattern.

Why is there such a long chain of dormant volcanoes connected to the active volcanoes in Hawaii? The most common explanation is mantle plumes, caused by processes of Rayleigh–Taylor instability. Tectonic plates drag oceanic over these plume-based hotspots, which “poke holes” into the lithosphere. Like fabric in a sewing machine…

Why does this seamont chain “change direction”? Magnetic evidence shows the plates simply changed direction, some 40 million years ago. 

Volcanoes create new crust, which is carried along on a conveyor belt, for consumption in the trenches. In this sense, oceanic crust are perpetually being recycled, with the creation of new and the destruction of old crust occurring simultaneously. This explains two salient facts: oceanic crust is much younger and thinner than continental crust.

As a result of this conveyor-like motion, the thin and mobile oceanic crust slowly “squeezes” continental land mass. This is the basis of orogony, the science of mountain formation. It’s fun to think about, especially when you’re traveling across these tremendous landmarks…

Most mountains are the coastline. Why are the Himalayas closer to the interior? Rather than oceans exerting compressive force on Asia, the Himalayas were formed by the entire subcontinent of India slowly moving North, and ultimately engaging in a slow-motion collision with the Eurasian landmass.

Oceanic crust doesn’t last long before being recycled. Continental crust has a talent for persisting, and growing increasingly thick. Here, the concept of geological province may help. Some continent crust is truly ancient, massive, and deep: these are called cratons. It is primarily in these 2 billion year old rocks that we find kimberlite, the stuff that contains diamonds. 

The Supercontinent Cycle

As you can see, there is no room for doubt that continents move. Indeed, GPS is able to detect continental drift in real time (arrows represent the direction and magnitude of drift). 

Let’s regroup. We know how the continents are arranged today, and are able to infer some information about other time periods. How much information, exactly? 

Looking forward, we have a fairly good idea of what will happen during the next 50 million years. It doesn’t take a rocket scientist to look at the GPS data above and conclude that Africa will collide with Europe, for example. But even though continents move very slowly and predictably on human time scales, after a certain amount of time our models begin to outstrip our data.

Looking backward, we have much more data to use in reverse-engineering previous geological periods. For example, we’ve already seen coastline-matching and mountain ridge evidence suggesting that Africa and South America were adjacent during the reign of supercontinent Pangaea, some 300 million years ago. 

Here is a reasonably high-quality animation of continental drift.

So that’s Pangaea. We also have solid evidence for another supercontinent called Rodinia some 700 mya. 

Our understanding of these two supercontinents is surprisingly complete. However, our ability to reverse engineer the past becomes less precise (and correspondingly, more controversy-ridden) as you go far beyond 1000 mya. Nevertheless, most geologists think they can make out the existence of four more supercontinents in their data. 

Mineralogy provides some evidence for the existence of supercontinents: certain minerals are only formed during these periods. Below is the formation history of molybdenite; similar graphs exist for other minerals. Further, magnetic imprints and radiometry allow us to glimpse the spatial organization or extinct supercontinents.

Why so many supercontinents? Consider again the story of Pangea. It used to be happily unified. But then a transcontinental rift occurred, separating what is now Africa and South America. Rifts occur where convection currents pull apart a single plate, and the in-between land sinks; modern-day rifts exist under the Red Sea, and the East African Rift Valley. 

During a supercontinent, there is a single continuous clump of water. After a transcontinental rift, a new ocean forms inside the rift (in our case, the Atlantic). The Atlantic Ocean is growing, the Pacific Ocean is shrinking. This process will continue until the Pacific Ocean is no more. A single ocean, and a single supercontinent. This is the supercontinent cycle

Biogeography

Animals have been around for some 700 million years. Dead animals sometimes leave behind fossils. 

Species are composed of populations: members of a species that live adjacent to one another. These populations tend to occupy a continuous stretch of land. Why? Regardless of where speciation occurs, population have only one way to spread out: walking.

The distribution of fossils starts to make more sense when you recall where the continents existed when these organisms lived.

Continental drift doesn’t just shed light on extinct species, but also living ones. An example to whet your appetite:

Why are marsupial mammals largely confined to Australia? By the time placentas were invented, Australia had separated from Pangaea.

Finally, biogeography is a predictive science: we can use it to make predictions about where to find fossils. Paleontolists can and do consult with geologists to figure out where to look in today’s rocks to find yesterday’s animals. Did you think the transitional form Tiktaalik was found by accident? No: Neil Shubin looked at species on either side of the “gap”, and reviewed when & where they lived. He then interpolated the spacetime location of the transitional forms. By “replayed the clock” to figure out where on contemporary Earth to look: his team went to look at specific strata in Swedish rocks, and the rest is history.

In closing, a few interesting parallels between geology and biology are worth noting:

  • Tectonic theory explains continental drift, just as natural selection explains common descent. 
  • More recently, we can directly observe continental drift with GPS data; just as we can now directly observe speciation. 

Takeaways

  • Continents move. South America used to be connected to Africa. We can even see continents drift using GPS.
  • Continental drift occurs because the Earth’s core is hot, and it creates convection currents that push on tectonic plates above.
  • Mountains are created by plates squishing into one another. 
  • Some volcanos are formed by mantle plumes “poking holes” into otherwise solid plates.
  • Ocean crust is “recycled” relatively rapidly. Continental crust persists as cratons.
  • Continents regularly coalesce into supercontinents, then dispersal by a transcontinental rift. This is the supercontinent cycle
  • The history of life coexists with continental drift. We can use the Earth sciences to constrain our knowledge of common descent.

[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.

 

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.

[Excerpt] How Language Evolved

Part Of: Language sequence
See Also: When Language Evolved
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).

Language Evolution_ Linear vs Recursive Grammar (1)

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.

Language Evolution_ Linear Grammar

[Excerpt] When Language Evolved

Part Of: Language sequence
See Also: How Language Evolved
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.

The Walking Ape: why our ancestors first stood up

Part Of: Anthropogeny sequence.
Content Summary: 1600 words, 16 min read

For all his noble qualities, godlike intellect, and exalted powers, man still bears in his bodily frame the indelible stamp of his lowly origin.

– Charles Darwin, Descent of Man

Setting The Stage

Common descent denotes the discovery that all species are related: that living organisms reside in a single tree of life. Homo Sapiens is no exception. We diverged from other hominoids (great apes) some 7 mya. During that time period, fossils more than 6,000 individuals from dozens of bipedal ape species.

Bipdality_ Hominin Phylogeny

Today, we explore why apes became bipedal. But first, the evolution of apes.  

Primate Evolution

Primates are mammals with flat nails instead of claws, grasping hands and feet, a highly developed visual system. They are highly iteroparous (long juvenile period) and have large brains to support the complex needs of group living. Primates are known for their symbolic dominance hierarchy, friendship mediated by grooming and mindreading (making inferences about the mental state of their peers).

Apes are primates that hang from branches (no tail), and even larger brains that promote behavioral flexibilities. Apes are known for coalitional warfare, group-specific cultural behaviors, flexible group signaling (e.g., mobbing), and tool-making.

The primate lineage emerged in the Paleocene (60 mya); apes in the Miocene (20 mya).

Bipedality_ Geological Periods (1).png

Without a tail (and in a “dead-end” body plan that precludes growing it back), apes increasingly relied upon behavioral flexibility to mitigate their comparative immobility. A monkey is an ecological specialist; the ape lineage was populated by generalists.

Apes flourished in the early and middle Miocene (20-10 mya). But they began to die out, starting in the late Miocene (10 mya). Today, there are hundreds of extant species of monkeys, and only five apes (gibbons, gorillas, orangutans, chimps and bonobos).

Evolution and progress are not synonymous. The ape branch of the tree of life is sparse because we are a failed lineage.

The failure of our ancestors seems to have been driven by a radiation from earlier primates (monkeys) in what can be called revenge of the specialized. It became increasingly difficult for generalized omnivorous species to find niches that were not more effectively exploited by a whole host of small-sized specialist monkeys.

Amidst this harsh inter-primate competition, it is interesting to note that modern apes are substantially larger than their Miocene ancestors. An increase in the body size of living apes and humans may well represent an evolutionary response to competition from monkeys.

We turn now to the question of bipedality. Before we can address why apes stood on two legs, we must first understand the anatomy of bipedality.

The Anatomy of Walking

The main anatomical structure that changed was the pelvis. The pelvis is not a single bone, but rather three bones glued together by cartilage. As we will see shortly, bipedality requires shortening of the ilium. 

Bipedality_ Pelvis Bones (1)

Walking is a pendulum-like motion. Most of the time one foot is off of the ground. This provides a stabilization problem. To solve this, bipedal animals have abductor muscles. You can actually feel these yourself: next time you walk around, feel the muscle on your hips flex (but only the muscle on the side of the weighted foot).

Bipedality_ Abductor Muscles (4)

Abductor muscles aren’t enough, however. In order to further stabilize a two-legged gait, the legs must be brought closer together. Adjusting the femur angle brings the center of gravity closer together:

Bipedality_ Knee

Finally, to improve the energy efficiency of walking, the human foot transitioned from a grasping surface to an energy-transfer platform.

Bipedality_ Foot Differences (3)

We have so far discussed four features of bipedal living. Here is a more complete list:

  1. pelvis shape (smaller ilium)
  2. pelvis musculature (abductor muscles)
  3. femur angle (more “knock-kneed”)
  4. feet (platform instead of grasping tool)
  5. foramen magnum angle (how the skull attaches to the spine),
  6. shape of the spine (bipedal spines are S-shaped), and
  7. reduced arm length (no longer needed to contact the ground)

The definition of hominin is bipedal ape. Little surprise then, that even the earliest hominin (Sahelanthropus Tchadensis) has at  least one feature associated with bipedalism. As we move to more recent species, we can see increasingly “classical” body plans:

Bipedality_ Anatomical Features (1)

Bipedality also explains why human beings suffer from:

  • Lower back pain. For hundreds millions of years, the spine was housed on a horizontal chassis. Switching to a vertical chassis places a lot of pressure on the lower spine. Zebras don’t suffer from lower back pain as much as human beings.
  • Hernias. The strain is not limited to the skeleton. Pressure also dramatically increases in the lower abdomen, causing an unusually high rates of hernias for human beings. In fact, one of the distinguishing characteristics of human beings is our smooth, fatty skin. We preferentially store fat subcutaneously to combat the pressure in our abdomen.

Theories of Bipedality

The fact that African apes became bipedal around 6 mya is not particularly interesting. A more interesting question is why African apes became bipedal. How did bipedality amplify the hominin niche?

There is no shortage of theories. Here are six:

  1. Brachiation (arm-based locomotion via branch-swinging) responsible for the postcranial features we share with apes.
  2. Arboreal apes modified their vertical climbing to walk bipedally along thick branches in the canopy.
  3. Bipedalism emerged from the need to carry babies, food, and other objects back to base.
  4. An aquatic phase of foraging and avoiding predators in water.
  5. Predator avoidance in the savannah with frequent peering over tall grass.
  6. A thermal theory whereby savanna dwellers stand up to keep cool.

These theories leave much to be desired, however.

First, some disregard ecological data entirely. The last two theories rely on the savannah hypothesis: that standing on two legs was made advantageous as forests increasingly disappeared. But the savannah hypothesis is wrong. Bipedalism emerged 6 mya, but the savannah grasslands only appeared 2-4 mya.

Second, they disregard the incrementality of natural selection. Two-legged standing preceded true bipedal walking and should not be lumped with it.  We must conceive of an ape that can stand but not walk (Orrorin tugensis?), and an ape that can walk but not run (Australopithicus afarensis).

More generally, whenever we see a complex adaptive package like walking, it is immediately useful to explore prerequisite abilities. One natural way to conceptualize the increments is as follows:

Bipedalism_ Incremental Improvements (2)

 

The above image identify anatomical increments with each new behavioral capability. 

We are not looking for a single ecological incentive for bipedalism; rather, we need individual motives for each increment in the journey to bipedality.

What kind of niche would reward flexible hips and a straight back?

The Primacy of Ecology

To answer this question, we need to get familiar with African geology and ecology.

As the most common promoter of diversity, allopatric speciation occurs when some population becomes isolated from the broader gene pool. Typically, these episodes are caused by climate change: the species gets “locked in” to a particular area by encroaching deserts, and then expands to surrounding habitats once the desert recedes.

The African continent contains wet-spots (equational rain) and hotspots (deserts). During cold glacial periods, these wet-spots expand along an east-west axis. For warm interglacial periods, the hot-spots expand along a north-south axis.

Bipedality_ African Hot-Dry Cycles.png

There are two primary forests in Africa:

Bipedality_ Two Forests

During the most arid climatic phases, the desert corridor separating these forests would close, leading to genetic isolation and speciation.

Squat Feeding in the Eastern Littorals

What kind of ape would emerge from the Main Forest Block? Such species would remain conservative (change slowly) because their much larger range embraces a much wider range of different types of wooded habitats. In fact, we know that modern-day gorillas derive from this ecosystem.

What kind of ape would be forged by the Eastern Forest Littoral? This smaller, fragmented ecosystem would cause both selection and genetic drift to accelerate. There are several peculiarities to this ecosystem worth pointing out:

Bipedality_ East African Littoral Ecology

In short, apes isolated in East African littoral forests seem likely to have found a niche on the forest floor. The natural distribution of resources favors this interpretation; and the growing competition from monkeys would have made the canopy increasingly infeasible.

These ground apes faced strong selective pressure to improve their foraging efficiency. The chimp pelvis has a very long ilium, which “locks into” the ribcage. There are clear foraging benefits for a reduction in the ilium (flexible waist), and straightening of the back (improved visibility). 

Bipedality_ Squatting Posture.png

In short, the squat-feeding hypothesis explains why flexible hips and straight spines were selected in ground apes of the early Pleistocene.

Other adaptive explanations only become relevant in further increments of the transition to bipedality. In particular, starting around 4 mya, the African continent began to dry. This made fruit increasingly less concentrated, and more seasonal. Locomotion thus became increasingly necessary to get enough calories. 

In modern humans, walking is four times more efficient than chimpanzee knuckle walking. Of course, very ancient hominins like Ardipithecus Ramidus could walk, but were less efficient than the Australopiths (and us, for that matter). But clumsy walking merely needs to improve upon the kinematic efficiency of knuckle walking, which as we have seen is not hard to do.

Bipedalism is not universally advantageous. Hominins like us are half as fast as other apes, and we have lost the ability to gallop. Greatly reduced ability to change direction while running.  The earliest bipeds probably avoided open habitats because of their increased vulnerability to predation, preferring forest and riverine habitats instead.

Bipedalism_ Ecological Pressures (2)

The facilitation of walking and running was not the ecological reason why our ancestors began the journey towards bipedality. But once they started on this particular anatomical pathway, these applications became possible. Thus, it is only with hindsight that we can say that the ultimate worth of standing up, the hidden evolutionary prize, was the ability to find the way out of a sort of ecological cul-de-sac.

Concluding Thoughts

The squat feeding theory of bipedality, as well as several of the images of this post, are credited to Jonathon Kingdon, African zoologist and author of Lowly Origin. I highly recommend this text, for those curious to learn more.

Until next time.