The 700 Club

We’re getting to a time on the blog when Homo erectus (and Homo ergaster, if we accept that erectus-like African specimens are another species) give way to the very earliest ancestors of later species – modern humans, Neanderthals, and Denisovans. (Denisovans – known mainly from DNA rather than bones – are the contemporaries in East and Southeast Asia of Neanderthals in West Eurasia, and early sapiens in Africa.)

And what should we call the whole post-erectus gang of modern humans / Neanderthals / Denisovans / modern humans? Maybe we could call them all Homo sapiens, and use subspecies names for the three branches; then we modern humans would be Homo sapiens sapiens. Or maybe we should reserve the label Homo sapiens just for our branch. In that case, we could call the larger clade “The 700 Club,” (see below), although apparently someone else already has already taken that name.

A recent article from Alan Rogers (a colleague of mine in Anthropology at the University of Utah) and Ryan Bohlender and Chad Huff (Utah Anthropology PhDs) sheds light on this period. The authors look at the distribution of shared derived mutations in two modern human genomes (African and Eurasian) and two ancient genomes (Neanderthal and Denisovan). They fit a model involving past divergence times and population sizes to the data. The model says that about 700,000 years ago. a small population split from the rest of humanity and then quickly split again to give rise to the ancestors of Neanderthals and Denisovans. In other words, it looks like there was an Out Of Africa event in the Middle Pleistocene, well before the better known Out Of Africa event that gave rise to modern human populations around the world. The ancestors of Neanderthals and Denisovans then replaced Homo erectus in Eurasia, although the authors find signs that some erectus genes may have made it into the Denisovan gene pool. This also implies that Homo antecessor in Europe was a dead-end branch of Homo erectus, not a Neanderthal ancestor.

As paleoanthropologist John Hawks notes, in a commentary on the article, “Humans stand out among our close primate relatives as effective biological invaders. Our recent history has included range expansions into remote and harsh geographic regions, and invasions by some populations into areas long occupied by others.” We’ll be seeing more instances of this in days to come on the blog.

And here’s me on what a later history of population replacement might mean for the evolution of ethnicity and ethnocentrism.

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.

Quest for fire, or, Eisenhower steak

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, 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

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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.

Father’s Day

1.04 million – 987 thousand years ago

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.

.

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 was a good dad, mostly, when his kids were growing up. But here he is showing off; his family isn’t going to eat the lion.)

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

Calories and curves

1.38 -1.32 million years ago

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.

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:

Mannish boy

1.6 million years ago

Turkana Boy (KNM WT 15000), from West Turkana, Kenya, is a striking find: the most complete early human skeleton we’ve got.

In addition to confirming a lot about Homo erectus’s shift to not-totally-unlike-modern bipedalism, he also seems to be telling us something about Homo erectus’s not-really-modern-human life history. Turkana Boy is not a grown up, but he has his second molars erupted. If he were a modern human, this would make him about 12 years old. Based on this, a lot of earlier accounts of the kid suggested he had a lot of growing to do, and would have ended up being a really tall adult – over 6 feet. But the latest evidence is that he was only 8-9 years old when he died, and wouldn’t have grown much taller than his 5 foot 3 if he had lived. In other words, Homo erectus back in his day grew up a lot more quickly than modern humans, and probably didn’t have much of the secondary adolescent growth spurt (coming after a late childhood slowdown) that we see in modern humans.

This in turn, if it holds up, is telling us that life was a lot rougher back then. Humans hadn’t got their act together keeping juvenile mortality low, and there was still strong pressure to rush through childhood and get on to reproducing quickly. A lot of kids, like Turkana boy, didn’t make it.

Homo erectus

Evolutionary theory implies that the transition from one species to another takes many generations. There’s never going to be a point at which a non-human animal gives birth to a human offspring. But on the scale we use to measure things at Logarithmic History, the time 1.8 million years ago has a good claim to be the time when human beings began. Genus Homo has been around for a while, but there are major evolutionary changes around now in the human direction. We can start with geography. It’s now that we find the first hominins outside of Africa, at least as far as Georgia in the Caucasus. The Dmanisi fossils from Georgia can probably be assigned to the new species Homo erectus, albeit somewhat shorter and smaller-brained than later erectus. Homo erectus also appears around this time in Africa (or maybe a bit earlier in South Africa, according to recent findings.)

It’s still possible that hominins got out of Africa even before erectus.  A recent article came out suggests that Homo floresiensis, the famous diminutive “hobbit” from Flores island, Indonesia, has its closest affinities with African Homo habilis, raising the possibility of an earlier exit. It’s even possible that H. erectus evolved outside Africa from this earlier emigrant (so far undiscovered), and then some migrated back to Africa.

H. erectus has a bigger brain than earlier forms, and reduced jaws and teeth. And there are dramatic changes below the neck. Erectus has a body shape and size quite similar to ours. Strikingly, the changes in body form seem to be systematically related to distance running. Tendons in the feet and calves turn into springs that put a bounce in our running stride (but also rule out serious tree-climbing). Our neck gets longer and shoulders and head get more independent so we can swing arms for balance without twisting our heads from side to side. And the gluteus maximus becomes the largest muscle in the body, to prevent our bodies from toppling forward with each step. Homo erectus is the first hominin with a serious butt.

Moving from what we know to what we guess, it looks likely that Homo erectus had shifted to a new diet and a new mode of acquiring food. David Carrier argues that H. erectus was a persistence hunter, running after prey until they were exhausted. Human beings, although pretty poor sprinters, have a big advantage in distance running, in that our breathing is uncoupled from our running. This lets us run efficiently at whatever speed we choose. Most mammals, by contrast, have to breathe and run in synch, and pay a heavy price – wasting energy and overheating – for running at non-optimal speed. Bipedal dinosaurs enjoyed a similar advantage.

Like anything else in paleoanthropology, there are arguments about this. For example, fire may or may not have played a significant role at this early stage. We’ll cover some of these arguments in posts to come.

Amplifier lakes

1.83 – 1.74 million years ago.

(Posted a day late)

We’re now counting off past time at the rate of 100,000 years a day.

Paleontologists and paleoanthropologists are busy sorting out what was special about the climate and ecology of Africa, especially East Africa, that contributed to various phases of hominin evolution. (“Hominin” is the current label for everyone more closely related to us than to our closest living relatives, i.e. chimpanzees and bonobos. My spell checker wants me to change it to hominid, the old label.) For example, Elizabeth Vrba, a South African paleontologist, argued that about 2.5 million years ago East Africa experienced a “turnover pulse” that affected a number of species. As the climate shifted toward cooler weather, and grasslands expanded, there was a wave of extinction and speciation among antelopes and (arguably) hominins as well.

More recently, paleoanthropologists have argued that not just cooling or aridity per se, but climate variability played a major role in driving hominin evolution, with episodes of greater variability leading to various responses ­– extinction, habitat tracking, or greater behavioral flexibility – as suggested in the diagram below.

More specifically, it looks like there were particular times when lakes were flickering in and out of existence along the Eastern and Western arms of the East African Rift Valley. Between just under 3 million years ago and just under 1 million three episodes stand out: around 2.7-2.5 mya, 1.9-1.7 mya, and 1.1-0.9 mya. These happen at intervals of 800,000 years, and may be tied to very long cycles in the eccentricity of Earth’s orbit. Within each of these episodes, the Rift Valley was home to large numbers of “amplifier lakes.” These lakes formed briefly during short intervals of high precipitation, and then evaporated quickly, making for a rich (sometimes) but also a particularly challenging environment.

Tellingly, it looks like these episodes were also associated with important events in hominin evolution. of 15 hominin species that evolved in this period, 12 appeared during these episodes.

This story, and much more, are set out in Lewis Dartnell’s excellent recent Origins: How Earth’s History Shaped Human History. However it is a ways from being settled science: here is a review of some of the problems with identifying ecological drivers of human evolution (behind a paywall unfortunately). The coauthors include some of my colleagues at the University of Utah.