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.
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:
- 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.
- 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.
- 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?
- 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?
- Simple power politics. Political influence is easier to hold & retain if your group is the only “outsider”.
- 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.
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:
- carnivores tend to store fat in this way,
- mitigate the hernia risk associated with bipedality
- 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.
Our Cursorial Adaptations
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.
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.
- 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
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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.
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.
Today, we explore why apes became bipedal. But first, the evolution of apes.
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).
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.
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).
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:
Finally, to improve the energy efficiency of walking, the human foot transitioned from a grasping surface to an energy-transfer platform.
We have so far discussed four features of bipedal living. Here is a more complete list:
- pelvis shape (smaller ilium)
- pelvis musculature (abductor muscles)
- femur angle (more “knock-kneed”)
- feet (platform instead of grasping tool)
- foramen magnum angle (how the skull attaches to the spine),
- shape of the spine (bipedal spines are S-shaped), and
- 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 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:
- Brachiation (arm-based locomotion via branch-swinging) responsible for the postcranial features we share with apes.
- Arboreal apes modified their vertical climbing to walk bipedally along thick branches in the canopy.
- Bipedalism emerged from the need to carry babies, food, and other objects back to base.
- An aquatic phase of foraging and avoiding predators in water.
- Predator avoidance in the savannah with frequent peering over tall grass.
- 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:
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.
There are two primary forests in Africa:
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:
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).
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.
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.
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.
The Universality of Cooking
Cooking is a human universal. It has been practiced in every known human society. Rumors to the contrary have never been substantiated. Not only is the existence of cooked foods universal, but most cuisines feature cooked foods as the dominant source of nutrition.
Raw foodists comprise a community dedicated to consuming uncooked food. Of course, compared to historical hunter-gatherers, modern raw foodists enjoy a wide variety of advantages. These include:
- Elaborate food preparation (pounding, purees, gently warming),
- Elimination of seasonal shortages (supermarkets)
- Genetically enhanced vegetables with more sugar content and fewer toxins.
Despite these advantages, raw foodists report significant weight loss (much more than vegetarians!). Further, raw foodists suffer from increasingly severe reproductive impairments, which have been linked to not getting enough energy.
Low BMI and impaired reproduction are perhaps manageable in modern times, but are simply unacceptable to hunter-gatherers living at subsistence levels.
The implication is clear: there is something odd about us. We are not like other animals. In most circumstances, we need cooked food.
The Energetics of Cooking
Life exists to find energy in order to make more copies of itself. Feeding and reproduction are the twin genetic imperatives.
Preferences are subject to natural selection. The fact that we enjoy cooked food suggests that cooking provides an energy boost to its recipients. The raw-foodist evidence hints towards this conclusion as well. But there is also direct evidence in rats that cooking increases energy gains.
In the following experiments, rat food was either processed/pounded, cooked, neither, or both. After giving this diet over the course of four days, rats in each condition were weighed.
For starches (left) and meat (right), cooking is by far more effective at preventing weight loss and promoting weight gain. Tenderizing food can sometimes help, but that technique pales in comparison to cooking.
The above results were taken from rats. But similar results have replicated in calves, lambs, piglets, cows, and even salmon. It seems to be universally true that cooking improves the energy derived from digestion, sometimes up to 30%.
How does cooking unlock more energy for digestion?
First, denaturation occurs when the internal bonds of a protein weaken, causing the molecule to open up. Heat predictably denatures (“unfolds”) proteins, and denatured proteins are more digestible because their open structure exposes them to the action of digestive enzymes.
Besides heat, three other techniques promote denaturation: acidity, sodium chloride, and drying. Cooking experts constantly harp on these exact techniques, because it aligns with eating preferences.
Second, tender foods is another boon to digestion, because they offer less resistance to the work of stomach acid. If you take rat food, and inject air into the pellets, that does not augment denaturation. Nevertheless, softening food in this way improves the energy intake of the rat.
Cooking does have negative effects. It can cause a loss of vitamins, and give rise to long-term toxic molecules called Maillard compounds, which are linked to cancer. But from an evolutionary perspective, these downsides are overshadowed by the impact of more calories. In subsistence cultures, better fed mothers have more, happier, and healthier children. When our ancestors first obtained extra calories by cooking their food, they and their descendants past on more genes than others of their species who ate raw.
A Brief Review of Human Evolution
The most recent common ancestor of humans and chimpanzees lived 6 mya (million years ago). But the first three million years of our heritage are not particularly innovative, anatomically. The australopiths were essentially bipedal apes. They could walk comfortably, but retained their adaptations for tree living as well. There is some evidence that australopiths acquired food from a new source: tubers (the underground energy storage system of plants).
Climate change is responsible for the demise of the australopiths. Africa began getting dryer 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 (underground storage organs of plants) from backup to primary food. In contrast, the habilines (e.g., Homo Habilis) took a different strategy: meat eating. These creatures inherited tool making from the late australopiths (Mode 1 tools, the Oldawan industry- was discovered in Ethiopia 2.6 mya), and used these tools to scrape meat off of bones). The habilines are more ecologically successful, and lead to:
- 1.9 mya: The erects (e.g., Homo erectus/ergastor) with significantly larger brains and near-modern anatomies.
- 0.7 mya: The archaics (e.g., Homo Heidelbergensis) appear, who eventually give rise to the Neanderthals, Denisovans, and us.
- 0.3 mya The moderns (e.g., Homo Sapiens) emerge out of Africa, and completely conquer the globe.
Here is a sketch of how our body plans have changed across evolutionary time:
The transition from habiline to erects deserves a closer look. We know erects evolved to be persistence hunters. But a number of paradoxes shroud their emergence:
- Digestive Apparati. The erect diet appears to be mainly meat and tubers. Both require substantial jaw strength and digestive apparati. Yet the Homo genus features a dramatically reduced digestive apparatus. How was smaller mouths, weaker jaws, smaller teeth, small stomachs, and shorter colons an adaptive response to eating meat and starches?
- Expensive Tissue. Australopiths brain size stayed relatively constant at 400 ccs (10% of resting metabolism). Erect brains began to grow. This transition ultimately yielded a 1400 cc brain (20% of resting metabolism) in archaic humans. How did the erects find the calories to finance this expansion?
- Time Budget. The above anatomical features of erects are geared towards endurance running, which suggests that their lifestyle involved persistence hunting. Chimps have about 20 minute intervals in between searching for & chewing food. Thus, chimps can only afford to spend 20 minutes hunting before giving up. How did erects perform the risky behavior of persistence hunting, which consumes 3-8 hours of time?
- Thermal Vulnerability. As part of their new hunting capabilities, erects became the naked ape (with a new eccrine sweat gland system to prevent overheating). But Homo Erectus also managed to migrate to non-African climates such as Europe. How did these creatures stay warm?
- Predator Safety. Erects lost their anatomical features for arboreal living, which suggests they slept on the ground. Terrestrial sleeping is quite dangerous on the African savannah. How did erects avoid predation & extinction?
All of these confusing phenomena can be explained if we posit H. erectus discovered the use of fire, and its application in cooking:
- Digestive Apparati. As we have seen, the primary role of cooking is to “externalize digestion”, and to increase the efficiency of our digestive tract. Cooked meat and starches are incredibly less demanding to process than their raw alternatives. This explains our reduced guts. By some estimates, the decrease in digestive tissue corresponds with a 10% energy savings by our erect ancestors.
- Expensive Tissue. Cooking increases the metabolic yield of most foodstuffs by ~30%. For reference, a 5% increase in ripe fruit for chimpanzees reduces interbreeding interval (time between children) by four months. 30% is an absurdly large energy gain, enough to “change the game” for the erects..
- Time Budget. Cooking freed up massive amounts of time otherwise spent chewing. Chimpanzees can take 4-7 hours per day chewing; humans only need one hour per day. This frees up massive amounts of time, which can be used for e.g., hunting.
- Thermal Vulnerability. It is very difficult to explain a hairless Homo Erectus thriving on the colder Asian continent without control of fire.
- Predator Safety. It is very difficult to explain how erects were not preyed upon to extinction without fire to identify & deter predators. Hadza hunter-gatherers comfortably sleep through the night, typically by taking turns “on watch” while the others rest.
The Archaeological Record
We are positing that erects learned to create and controlling fire 2 mya. Is that a feasible hypothesis?
Habilines had learned how to create stone tools 2.6 million years ago. By the time of the erects, techniques to create these tools had persisted for 600,000 years. So it is safe to say that our ancestors were able to retain useful cultural innovations.
Independent environmental reasons link fire-making with H Erectus. The Atlas mountain range is the most likely birthplace of this species, and this dry area fires triggered by lightning are an annual hazard. Hominins living in such environments would be more intimately familiar with fire than those with less combustible vegetation zones.
Erects would have seen sparks when they hit stones together to make tools. But the sparks produced by many kinds of rock are too cool to catch fire. However, when pyrites (a fairly common ore) are hit against flint, the results are used by hunter-gatherers to reliably produce fire. The Atlas mountain range is renowned for being exceptionally rich in minerals:
Why is Morocco one of the world’s great countries for minerals? No glaciers! Many of the world’s most colorful minerals are found in deposits at the surface, formed over time by the interaction of water, air and rock. Glaciers remove all of that good stuff (as happened in Canada recently, geologically speaking) – and with no recent glaciation, Morocco hosts many fantastic occurrences of minerals unlike any in parts of the world stripped bare during the last Ice Age.
Since this mountain range contains pyrites, early erects could have found themselves inadvertently making fire rather often.
Once it is created, fire is relatively easy to keep going. And it does not take much creativity to stick food a fire. Moreover, modern-day chimps prefer cooked food over raw; it is hard to imagine H Erectus finding cooked food distasteful. All of these considerations suggest an early control of fire is at least plausible.
We can consult the archaeological record to see record of man-made fire (i.e., hearths). This is bad news for the cooking hypothesis! There is strong evidence for hearths dating back to 800 mya and the advent of archaic humans. Before then, there are six sites that seem to be hearths; but these are not universally acknowledged as such.
But absence of evidence isn’t evidence of absence, right?
No! That idiom is wrong. Silence is evidence of absence. It’s just that the strength of the evidence depends on the nature of the hypothesized entity.
- If you think an unidentified planet orbits the Sun, a lack of evidence would weigh heavily against the hypothesis.
- If you think an unidentified pebble orbits the Sun, a lack of evidence doesn’t say much one way of the other.
Wrangham argues that evidence of hearths are more fragile than e.g. fossils, and points to facts like there are zero hearths recorded for modern humans during European “ice ages” – but we know these must have existed. It is possible that the contested hearth sites will ultimately be vindicated, and that we just can’t see much evidence.
Despite these claims about evidential likelihood, the silence of the archaeological record is undeniably a significant objection to the theory.
Weighing The Evidence
Is the cooking hypothesis true? Let us weigh the evidence, and contrast it with alternative hypotheses.
The most plausible alternative hypothesis is that archaic humans H. Heidelbergensis discovered cooking. But the emergence of that species involved an increase in brain size, and more sophisticated culture & hunting technology. Neither adaptation seems strongly connected to cooking. In contrast, the H. Erectus adaptations would have all been strongly affected by cooking.
Moreover, alternative hypotheses must still answer the five paradoxes of hominization:
- Digestive Apparati. Why did erects evolve smaller mouths, weaker jaws, smaller teeth, small stomachs, and shorter colons?
- Expensive Tissue. How did the erects find the calories to finance more brain tissue?
- Time Budget. How could erects afford spending 3-8 hours per day engaged in the risky strategy hunting?
- Thermal Vulnerability. Erects also managed to migrate to non-African climates such as Europe. How did these creatures stay warm?
- Predator Safety. Erects slept on the ground. How did they avoid predation?
The habilines ate meat. It is unclear how they did so (hunting or scavenging), but we have strong evidence that they did. Meat is a much higher quality food than tubers (cf. paranthropes) or fruit (cf. chimpanzees). The meat-eating hypothesis argues that meat eating was the primary driver of hominization.
Meat-eating resolves the Expensive Tissue paradox (meat allows for brain growth) and Digestive Apparati (carnivores are known to have smaller guts). But it doesn’t address why a meat-eater would develop smaller canines. And it struggles to explain how the reduction in gut size is compatible with the tuber component of the erect diet. And what about time budget, thermal vulnerability, and predator safety? The meat eating hypothesis fails to address these paradoxes entirely.
Which is more likely to occur in the next twenty years: undisputed evidence for early control of fire, or an alternate theory that resolves all five hominization paradoxes?
My money is on the former.
- Wrangham (). Catching Fire: How Cooking Made Us Human
- Aiello & Wheeler(1995). The expensive tissue hypothesis: the brain and the digestive system in primate and human evolution.