Antecessor rising

A common way of demeaning another group is to call them cannibals. Roman pagans sometimes accused early Christians of cannibalizing infants during their secret ceremonies (a horror-show misreporting of the bread and wine of Christian communion?). Later on, medieval Christians sometimes accused Jews of murdering Christian infants and mixing their blood into Passover matzohs. In response to such libels, anthropologists have sometimes swung to the opposite extreme, occasionally even denying that cannibalism (not counting emergency survival cannibalism) was ever an established practice. But there is no serious doubt that human populations have sometimes practiced cannibalism, sometimes in the very recent past. In 1961, for example, Michael Rockefeller, traveling in search of tribal art, was killed and eaten by a group on the coast of New Guinea. Cannibalism can be unhealthy. For example handling and eating uncooked brains was responsible for the spread of kuru, a  gruesome prion disease, among the Fore of New Guinea. Human populations harbor genes that protect against prion diseases; this might be telling us that cannibalism was common among our ancestors.

At the Grand Dolina site in the Sierra de Atapuerca in northern Spain, the fragmentary remains of 6 people, mostly children, were discovered mixed in with animal bones and stone tools. Animal and human remains were treated the same. In both cases, cut marks show that flesh was cut from the bones. There’s no evidence that the human remains received any specially respectful treatment. Cannibalism is the most plausible explanation.

The researchers involved have proposed a new species name, Homo antecessor, for these and some other early European finds. And just last year, evidence came out about the relationship of antecessor to other humans: a study based on recovered proteins (not DNA) from antecessor tooth enamel finds that they are close to the common ancestry of modern humans, Neanderthals, and Denisovans.

Ice Age gear shift

833 – 789 thousand years ago

Around today’s date, there was a shift in the nature of glacial cycles.

But let’s back up a bit. Earth’s climate took a turn toward cool in the transition from Eocene to Oligocene, 35 million years ago (although with some warming in the Miocene). It was probably back then that much of Antarctica started being covered by ice. The establishment of open water all the way around Antarctica may have helped isolate and freeze the continent. And declining carbon dioxide levels, partly a result of weathering of rocks in the Himalayas, probably also made a difference. But it was back at the beginning of the Pleistocene, now dated to 2.5 million years ago, that the current Ice Age truly began, with glaciers covering large parts of northern North America and northern Europe.

Current Ice Age? Glaciers covering large parts of northern North America and northern Europe? This isn’t what the climate has been like for the past 12,0000 years. Within the current long Ice Age there have been long glacial periods and shorter interglacials, and we’re currently in an interglacial. Our own activities may have done something to prolong the interglacial, and stave off the return of the ice; more on this another day.

Three astronomical cycles govern the rhythm of glacial and interglacial. There’s a 100,000 year cycle as Earth’s orbit changes from somewhat more elliptical to somewhat more circular. There’s a 40,000 year cycle as Earth’s axis shifts from slightly more tilted (24.5 degrees off vertical) to slightly less (22.1 degrees); it’s currently tilted at 23.5 degrees. And there’s a 21,000 year cycle generated as the Earth precesses – wobbles like a top. Right now the North Pole is pointed at Polaris, and the Sun very recently started rising in the constellation Aquarius at the Spring equinox: hence the Age of Aquarius.

(An even longer 400,000 year cycle might have been involved earlier in human evolution, in establishing intervals in which “amplifier lakes” flashed in and out of existence in the African rift valley. More here.)

Between 2.5 million and 800,000 years ago, the glacial/interglacial alternation was dominated by the 40,000 year cycle. But beginning about 800,000 years, there has been a gear shift: the 100,000 year cycle has been dominant and swings in climate have been more extreme. (In Africa however the 21,000 year cycle is more important for alternations between rainy and dry. Africa is in a dry state now.)

One of the startling findings to come out of the last few decades of work on ice cores from Greenland and Antarctica is that not only have there have been huge long-term changes in climate, but there have also been extreme short term shifts, probably connected with changes in ocean currents. There have been a number of occasions over the last hundreds of thousands of years during which average temperatures shifted by 10-20 degrees Fahrenheit (5-10 degrees Celsius) for a millennium, or even for a century or less! (During the last 10,000 years, however, the climate has been unusually stable.)

This is bound to have had strong effects on human beings. Two anthropologists, Robert Boyd and Peter Richerson, who work on mathematical models of cultural evolution, have a general theory of how this pattern of oscillations might have affected human evolution. They argue that human adaptation takes place on multiple time scales. On very long time scales, human beings adapt to changes in the environment genetically. On very short time scale, human beings adapt to change through individual learning. But when change happens on intermediate time scales, adaptation takes place through social learning. With changes on intermediate time scales, your ancestors may not have enough time to adapt genetically to the current climate, but things may be stable for long enough that your culture and the wisdom of the elders have a lot to teach you about how to cope. One of the really distinctive features of human beings, maybe even The Secret of Our Success is that we are, more than any other creature, a cultural animal, with high-fidelity cultural transmission; this trait may have been shaped by the nature of climate change especially over the last 800,000 years.

Father’s Day

(This comes a day after US Father’s Day. My grilling responsibilities kept me from posting it on the day.)

One man draws out the wire, another straights it, a third cuts it, a fourth points it, a fifth grinds it at the top for receiving the head; to make the head requires two or three distinct operations; to put it on, is a peculiar business, to whiten the pins is another; it is even a trade by itself to put them into the paper; and the important business of making a pin is, in this manner, divided into about eighteen distinct operations, which, in some manufactories, are all performed by distinct hands.

Adam Smith famously observed the enormous advantage to be gained from a division of labor in the manufacture of pins. But in one form, the division of labor is far older than Smith’s pin factory: virtually every human society has a division of labor by sex. Here’s a chart from anthropologist George Murdock on the sexual division of labor across cultures.

.murdock

M Exclusively male
N Predominantly male
E Equal/equivalent for both sexes
G Predominantly female
F Exclusively female
Index is weighted average, male vs.female

The sexual division of labor is an unusual arrangement among animals: not just males and females cooperating in provisioning offspring (birds do it, wolves do it), but doing very different jobs.

It seems very likely that by today’s date on Logarithmic History, Homo erectus had a sexual division of labor, in particular a male specialization in hunting large animals. But there is a problem in figuring out how this arrangement could have gotten started. Smith listed “a tolerable administration of justice” as one ingredient in economic progress: his pin factory would have run into problems without property rights to keep people from swiping pins. In the context of the sexual division of labor, a similar problem arises if we assume that hunting is a form of “paternal provisioning.” How could this ever get off the ground, given an initial condition of promiscuity or alpha-male polygynous mating? (If we assume that monogamy is already in place, the problem is less serious. When paternal provisioning occurs in other mammalian species, it apparently evolves out of a prior condition of scattered monogamous pairs. However this sequence seems improbable for human ancestors.)

Maybe the assumption about hunting as paternal provisioning is wrong. Maybe hunting is about showing off, not providing for a family. (Hemingway is showing off; his family isn’t going to eat the lion.)

hemingway lion

But a recent article considers another possibility: a “Dad” who provisions his family may succeed in a world of “Cads” if there are strong complementarities in economic activities between males and females, i.e. a sexual division of labor. In this respect, human dads may really be something special.

Quest for fire

930 – 881 thousand years ago

On June 3 on Logarithmic History, our ancestors had gotten as far as steak tartare. Now it’s time for an Eisenhower steak (cooked directly on the coals; see below).

What really distinguishes humans from other animals? We’ve covered some of the answers already, and will cover more in posts to come. But certainly one of the great human distinctions is that we alone use fire. Fire is recognized as something special not just by scientists, but in the many myths about how humans acquired fire. (It ain’t just Prometheus.) Claude Lévi-Strauss got a whole book out of analyzing South American Indian myths of how the distinction between raw and cooked separates nature from culture. (I admit this is where I get bogged down on Lévi-Strauss.)

Until recently the story about fire was that it came late, toward the latter days of Homo erectus. But Richard Wrangham, a primatologist at Harvard, turned this around with his book Catching Fire (which is not the same as this book), arguing that the taming of fire goes back much earlier, to the origin of Homo erectus. Wrangham argues that it was cooking in particular that set us on the road to humanity. Cooking allows human beings to extract much more of energy from foods (in addition to killing parasites). Homo erectus had smaller teeth and jaw than earlier hominins and probably a smaller gut, and it may have been fire that made this possible. Cooking is also likely to have affected social life, by focusing eating and socializing around a central place. (E O Wilson thinks that home sites favored intense sociality in both social insects and humans.)

Surviving on raw food is difficult for people in a modern high-tech environment and probably impossible for people in traditional settings. Anthropologists are always looking for human universals, and almost always finding exceptions (e.g. the vast majority of societies avoid regular brother-sister marriage, but there are a few exceptions, including Roman Egypt and Zoroastrian Iran). But cooking seems to be a real, true universal. No society is known where people got by without cooking. Tasmanians, isolated from the rest of the world for 10,000 years, with the simplest technology of any people in recent history, had lost the art of making fire, but still kept fires going and still cooked.

Recent archeological finds have pushed the date for controlled use of fire back to 1 million years ago (see today’s tweet on Wonderwerk cave), but not all the way back to the origin of Homo erectus. This doesn’t mean Wrangham is wrong. Fire sites don’t always preserve very well: we have virtually no archeological evidence of the first Americans controlling fire, but nobody doubts they were doing it. It could be that it will be the geneticists who will settle this one. The Maillard (or browning) reaction that gives cooked meat much of its flavor generates compounds that are toxic to many mammals but not (or not so much) to us. At some point we may learn just how far back genetic adaptations to eating cooked food go.

An alternative to an early date for fire, there is the recent theory that processing food, by chopping it up and mashing it with stone tools, was the crucial early adaptation.

Whenever it is exactly that humans started cooking, the date falls in (Northern hemisphere) grilling season on Logarithmic History, so you can celebrate the taming of fire accordingly. It doesn’t have to be meat you grill. Some anthropologists think cooking veggies was even more important. I recommend sliced eggplant particularly, brushed with olive oil to keep it from sticking, and with salt, pepper, and any other spices.

On the other hand, Homo erectus probably appreciated a good Eisenhower steak, cooked directly on the coals. (Yes, this actually works pretty well.)

Eisenhower Coal-Fired Steak

Named for the 34th president of the United States, who liked to cook his steaks directly on the coals, this preparation will create a crunchy, charred exterior with rosy, medium-rare meat inside.

Lump hardwood coals work better than briquettes for this recipe because they burn hotter. Be sure you use long-handled tongs. (Sorry, this method is for charcoal or wood grilling only.)

You might find an uneven exterior crust, especially when using lump charcoal, because it is irregularly shaped (unlike the uniform briquette pillows). If that happens, try to position the steak so that it is more directly on the coals and gets an even char. Clasp the steak in the tongs and rap the tongs against the edge of the grill to knock off the occasional clinging ember. If you have some ash, flick it off with a pastry brush.

Make Ahead: The steaks can be seasoned and refrigerated up to 4 hours in advance. Bring them to room temperature before they go on the fire.

INGREDIENTS
  • 1 teaspoon olive oil
  • Two 1 1/2-inch-thick boneless rib-eye steaks (about 28 ounces total)
  • 2 teaspoons coarse sea salt
  • 2 teaspoons freshly cracked black pepper

DIRECTIONS

Prepare the grill for direct heat. Light the charcoal; when the coals are just covered in gray ash, distribute them evenly over the cooking area. For a hot fire (450 to 500 degrees), you should be able to hold your hand about 6 inches above the coals for 2 or 3 seconds. Have a spray water bottle at hand for taming any flames. But use it lightly; you don’t want to dampen the heat too much, and some flames here are fine.

Meanwhile, brush the oil on the both sides of the steaks, then season both sides liberally with salt and pepper.

Once the coals are ready, place the steaks directly on the coals (see headnote). Cook, uncovered, for 6 minutes on one side, then use tongs to turn them over. Cook for about 5 minutes on the second side.

Transfer the steaks to a platter to rest for 10 minutes. Serve as is, or cut them into 1/2-inch-thick slices.

My handaxe

1,043 – 986 thousand years ago

By today’s date, Acheulean tools are well developed in Africa, and found in India too. Sophisticated tools like the Acheulean hand axe probably tell us something not just about cognition in relation to tool making, but also about social cognition. You wouldn’t make a hand axe, use it, and abandon it. Nor would you go to all the trouble if the biggest, baddest guy in the group was immediately going to grab it from you. So there is probably some notion of artifacts-as-personal-possessions by the time Acheulean appears.

Possession is a social relationship, a relationship between two or more individuals with respect to the thing possessed. Robinson Crusoe didn’t “own” anything on his island before Friday came along.

Linguists have noted something interesting about the language of possession that maybe tells us something about the psychology of possession: Expressions for possession are often similar to expressions for spatial locations. Compare spatial expressions:

João went to Recife.
Chico stayed in Rio.
The gang kept Zezinho in Salvador.

and corresponding constructions for possessions:

The Crampden estate went to Reginald.
The Hampden estate stayed with Lionel.
Thag kept axe.

Of course the Crampden estate didn’t go anywhere in physical space, but it still traveled in the abstract social space of possession. In some cases just switching from inanimate to animate subject will switch the meaning from locative to possessive. The Russian preposition y means at/near when applied to a place (People are at Nevsky street) but possession when applied to a person (Hat is “at” Ivan = Ivan has hat.)

What may be going on here: people (and many other creatures) have some mental machinery for thinking about physical space. That machinery gets retooled/borrowed/exapted for thinking about more abstract relationships. So the cognitive psychology of space gets retooled for thinking about close and distant social relationships, or time ahead and behind. In other words, we may be seeing a common evolutionary phenomenon of organs evolved for one purpose being put to another purpose – reptile jaw bones evolve into mammalian inner ear bones, dinosaur forelimbs evolve into bird wings. You can find Steve Pinker making this argument in his book The Stuff of Thought. And Barbara Tversky’s recent Mind in Motion: How Action Shapes Thought seems to make the argument at greater length. For a while most of the evidence of repurposing spatial cognition for more abstract relationships came from linguistics, but there’s now some corroboration from neurology.

And I’ve made the argument for the particular case of kinship: regularities in kin terminology across cultures tell us something about pan-human ideas of “kinship space.” (My kin and mybody parts are arguably the most basic, intrinsic primitive sorts of possessions, since long before my handaxe.) This implies that the evolutionary psychology of kinship has not just an adaptive component (adaptations for calculating coefficients of relatedness and inbreeding), but also a phylogenetic component  (homologies with the cognitive psychology of space).

We’ll see other possible examples, involving e.g. the evolution of speech sounds, as we move along.

Heather erectus

Or, Women Gotta Stick Together

(Here’s a link to the song, a satirical take on female solidarity from the show “Crazy Ex-Girlfriend”)

Because boys are much louder and less private than girls, it took me a while to begin to focus on girls’ behaviors. When I did, I was quite surprised to see that the stereotypes that apply to girls’ behavior around the world, such as “sugar and spice and everything nice,” did not fully describe what I was actually seeing girls do. … Girls spend a lot of time talking about other people in their lives … These discussions, however, are not composed simply of saying “nice” things about their family and friends. Often, they are dissecting the most negative aspects of another’s behavior. … Paradoxically, I … found out that two girls or two women talking do not typically help one another, other than to be reassuring. In fact, two unrelated females often can become fast enemies. Because they have so much in common, they need similar physical resources, and beginning in adolescence they may compete for the same men. This creates an inherent conflict in unrelated human females’ relations with one another. … How this plays out leads to some very confusing relationships.

Warriors and Worriers: The Survival of the Sexes. Joyce F. Beneson

As Darwin noted, adaptive evolution involves nsexual selection as well as the struggle for existence. Sexual selection is not simply about A surviving and reproducing, but more specifically about A reproducing at the expense of B. This may involve mate choice: A may succeed at the expense of B because he or she is more attractive to the other sex. Mate choice may have shaped both female and male traits in our species. Sexual selection can also involve contests within one sex over who mates with the opposite sex. There have been epochs in the history of our species when some men have acquired many more mates, and left many more offspring, than others, most likely by wielding violence, typically as part of a gang. 

Female-female sexual competition is less conspicuous, but still very real.It may have left its mark on women’s sexual physiology and behavior. One argument goes like this:

Ovulation is less conspicuous in our species than among many other primates. Unless we know them very well, we generally don’t have much idea who among the young women we run into is ovulating. The evolution of concealed ovulation at some point in the human line has been the subject of a lot of theorizing. Most of the theories invoke male mate choice: maybe men were more likely to stick around and provide for women who didn’t reveal when they were and weren’t ovulating. But recent work suggests that, in addition to male provisioning, female-female sexual rivalry and aggression may have been crucial. In an agent-based simulation in which females could secure mateships and provisioning by aggressing against rivals, “concealers” were able to out-reproduce “revealers” because they avoided aggression from other females. In other words, the concealment of ovulation in our species may reflect a long evolutionary history of estrus-shaming (my phrase, not the authors’).

What do women want?

1.10-1.05 million years ago

As we noted in the last post, human females conceal ovulation (no chimp-style monthly sexual swellings) but advertise nubility (with conspicuous fat deposits). Perhaps this has to do with sexual selection, via male mate choice (but see the next post for a different theory). But sexual selection may have operated in the opposite direction, on male anatomy, as well.

Males of most primate species have a baculum, or penis bone. Human beings and spider monkeys are the exceptions. (A mnemonic: the mammals with penis bones are PRICCs – primates, rodents, insectivores, carnivores, chiropterans=bats.) The baculum helps to retract the penis when it’s not in use, so males in our species, lacking a penis bone, have more conspicuous dangling organs than most primate males.

This information comes from a recent book The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World – and Us, by Robert Prum. Prum also cites a paper arguing that Adam’s “rib” (Hebrew tsela), the thing God used to make Eve (Genesis 2:21-23), was actually his baculum, providing a creationist explanation of “congenital human baculum deficiency.” (But check out a more skeptical take.) The book contains lots of interesting tidbits like this, although I don’t know that I buy its central argument, that sexual selection via mate choice is largely a result of non-adaptive aesthetic preferences.

Men’s penises lack something else found in most primate species: most male primates have keratinized spines on their penises. But a gene involved in the development of penis spines got turned off in our evolutionary lineage, some time after our split with chimps, but before our split with Neanderthals. We’re not sure why. Penis spines might be favored in promiscuously mating species if they help one male dredge out sperm left by earlier matings with other males. So (relative) monogamy in our lineage might remove the evolutionary advantage of spines. But a non-spiny penis might also be less sensitive, and make for more prolonged intercourse.

If all this doesn’t answer the question “What do women want?”, it at least narrows down the possibilities a bit: not men with bony, spiny penises, apparently.

Calories and curves

1.38 -1.32 million years ago

energyfat

This figure is from a neat recent paper comparing energy expenditure (TEE or Total Energy Expended) and fat among humans and our closest relations: chimpanzees (genus Pan), gorillas (Gorilla), and orangutans (Pongo). (The numbers are adjusted for differences in overall body mass.)

What stands out here is that humans are a high energy species. Also we carry a lot more body fat than the other great apes. This applies particularly to women, who need a lot of extra fat to meet the high energy demands of human infants. But it even applies to men. For both sexes, a high energy life style means you want to carry around an extra reserve of fat in case of emergencies.

We don’t know how long ago our ancestors decided to crank up their energy consumption. Maybe back with the rise of Homo erectus (just a few days ago on Logarithmic History). Or maybe later, when the typical modern human pattern of slow maturation was more firmly in place. At some point in the near future, we’ll actually nail down the specific genetic changes leading humans to accumulate more fat, and be able to put a date on the change. It may be that the distinctively human mating system also arose back then, with human females concealing ovulation (no chimp-style monthly sexual swellings) but advertising nubility (with conspicuous fat deposits appearing at puberty)

A high energy life-style also goes with extensive food sharing and changes in human kinship. (Here’s me, on beating Hamilton’s rule through socially enforced nepotism.)

Blood and brains

Humans are brainy animals. One way to show that is by looking at brain size: our species has the biggest brains, in relation to body size, of any animal. But there’s more to it than that. An earlier post covered the work of Susan Herculano-Houzel. She developed a technique for counting the number of neurons in a brain, or part of a brain. Among most mammals, big animals have a lower density of brain neurons, so they aren’t actually as brainy (measured by neuron number) as you’d think just based on their brain size. Primates however break the usual mammalian rule. Big primates have the same neuron density as little guys, so they really are quite brainy. And humans, with really big brains and (following primate rules) a high density of neurons, stand out even among primates as exceptionally brainy.

This work isn’t much help if we are looking at extinct hominins, when all we’ve got is their fossil skulls. But now there’s some interesting recent research with a new take on the subject. Brains need to be supplied with blood. The more energy they use, the more blood flow is needed. We can now figure out fairly accurately how much blood flow a brain is getting by looking at the size of the hole that lets the carotid artery in through the base of the skull. And then we can apply this technique to look at humans, and at extinct hominins. It turns out that humans are even more exceptional when we look at blood flow to the brain: we’re getting double the flow that you’d expect based on brain size alone.

blood brain

Early hominins however, Australopithecus and early Homo, aren’t very impressive upstairs, many with less blood flow to the brain than modern apes. Looking at the graph it looks like there are really two grades of brain evolution. In the lower grade, which includes early hominins and modern apes, there is a gradual increase over millions of years. (I’m just guessing here that the ancestors of chimps and gorillas millions of years ago were about as brainy as contemporary hominins, but we’d still like to find more fossils.) And then there is a big leap up to a higher grade with early Homo erectus, and a rapid increase after that. It looks like something major changed with the appearance of Homo erectus, either on the supply side – improvements in food supply making brains more affordable – or on the demand side – a greater fitness payoff to a high energy brain – or both.

Handaxe

1.46 – 1.39 million years ago

From around 1.4 million years ago, Acheulean hand axes appear in Africa. They will eventually show up in southwest Europe and as far east as India. Hand axes were long thought to be absent from further east, but now have been found sporadically in East Asia. (Bamboo might have been an alternative to stone in the east.) Wear analyses show that hand axes, “the Swiss Army knife of the Paleolithic,” were used for a variety of purposes: cutting wood, slicing meat, scraping hides.

The hand axe implies a great leap forward cognitively from earlier Oldowan tools (although you can flay an elephant with Oldowan flakes). People (let’s call them people) were not just choosing the right material and making the right hand movements, but choosing the right shape of stone, and imagining the hand axe inside it before they started.

Dietrich Stout, an experimental anthropologist at Emory University, has trained students to make modern-day Acheulean handaxes, and monitored their brains as they learn. (The students’ axes, after months of practice, still aren’t as good as the real thing.) See the video below: