Putting’ on the Ritz

173-164 thousand years ago.

It’s fancy dress day on Logarithmic History. Between 170 and 80 thousand years ago, people started wearing clothes. We know this from recent genetic studies showing that sometime during that period, probably closer to 170 kya, pubic lice and body (=clothing) lice diverged into two separate species. This is before the major exodus of modern humans from Africa, so it probably means clothing was not just about protection from high latitude winters. (There’s an even earlier split, three million years ago, between head lice and pubic lice, that probably means human ancestors had lost their fur. And there’s another story about the ancestors of East Asians picking up a different strain of head lice from non-sapiens humans that we may cover later.)

Lice are not just disgusting, but dangerous. On later dates, we’ll have occasion to see how louse-borne diseases like typhus have affected the course of history. But for now let’s forget about lice, and celebrate clothing, with Irving Berlin’s song about fancy duds, “Puttin’ On the Ritz,” covered below by a Moscow flashmob. (Also  relevant to the video is Barbara Ehrenreich’s book on dancing in history and prehistory Dancing in the Streets: A History of Collective Joy, although collective dancing isn’t something we can put a date on yet.)

Hello, Dali

dali

250 thousand years ago

This skull, from China, isn’t much like Homo neanderthalensis or modern Homo sapiens. Both Neanderthals and H. sapiens are specialized in different directions, in ways that aren’t just an automatic consequence of increasing brain size. In Neanderthals, the middle of the face is pulled way forward, in front of a football shaped braincase. In H. sapiens (us), the face is tucked well under the skull, beneath a globular braincase. (We’ll have more to say about these changes later: sapiens skull shape probably has to do with re-engineering the vocal tract.) The Dali skull by contrast looks like a generic transitional late Homo erectus / archaic Homo sapiens (the latter being just a wastebasket, “I dunno. Whaddayou think it is?” category). It isn’t totally clear where Dali belongs phylogenetically. It could be part of/ancestral to an East/Southeast Asian group called Denisovans. Denisovans have come to be known by their genes, which have been found in an ancient Siberian fingerbone, and (at low levels) in some modern Melanesians and Australian aborigines. What we don’t yet know for certain is whether Dali (and similar finds like the less securely dated Jinniushang skull) had these Denisovan genes.

Learn This One Weird Trick (Part Two)

… that humans use, and now you can too! (Continued from the previous post.)

recursion 3) Recursion. What if you have one mirror facing a second mirror, so the first mirror shows what’s in the second mirror, which shows what’s in the first mirror …? What if you take a chameleon, which tries to take on the color of its surroundings, and put it on a mirror? What if you point a video camera at the very screen that’s showing what the video camera is pointing at? What if (getting mathematical) you use a function in defining that same function? What if you use the cleaning attachment from your vacuum cleaner to suck dust off the vacuum cleaner itself? (Okay, the last one is a bit lame.) The basic idea in each of these cases is called recursion, which is a major concept in mathematics and computer science. Douglas Hofstadter’s Gödel, Escher, Bach is all about recursion. Some people think recursion – nesting ideas about ideas inside one another in a potentially infinite hierarchy, or (for syntax) phrases inside phrases — is central to human uniqueness. Noam Chomsky has lately been pushing a hard-core version of this argument. Here he is with Robert Berwick defending his view.

Related to the idea of recursion is the idea of “meta-representation”: not just having ideas about the world but having ideas about ideas, being able to put a box around a proposition, and then attaching a tag to it that says the equivalent of “This is true” or “This is false” or “This will be true later” or “Suppose this were true,” and then manipulating it accordingly. A nice little essay in “imagination,” elaborating this idea, is here from Simon Baron-Cohen, best known as an authority on autism.

4) Shared intentionality. Suppose you and I are friends with a couple, Fred and Wendy Smith. I tell you “I saw Wendy Smith kissing a man in the park yesterday.” Logically speaking, there’s nothing to say the man wasn’t Fred. But you’ll probably assume that I meant she was kissing someone other than Fred. Why? Well if the man had been Fred I could just as easily have said “I saw Wendy Smith kissing Fred in the park yesterday.” Since I didn’t say that, you assume I mean to convey the man wasn’t Fred. Note this only works if both of us try to pack as much relevant information into our sentences as possible and know the other person is doing the same. (If you think this sounds like recursion, you’re right.) Back in the 1950s, Paul Grice, a philosopher, worked out a lot of how we pack non-literal meanings into sentences. But the same principles are at work even when people are communicating non-linguistically. This leads to another theory of human uniqueness: human beings are uniquely good at developing shared intentions with one another: each party knows the other party is trying to communicate something, so they converge on the correct answer. People may have been doing this even before language evolved. Following up on this can quickly get you into game theory, where a central concept is “common knowledge”: not just “I know X” and “You know X,” but “I know X,” and “I know X is common knowledge,” and similarly for you. Here’s a philosophical treatment.

scleraBut you can skip the philosophy if you want and move on to a telling little piece of anatomy that’s relevant here. In most mammals, including chimpanzees, the sclera (white of the eyes) is not visible. It’s hard to tell where a chimpanzee is looking, easy for a human. Human eyes make it easy to cooperate in sharing attention, a first step in developing shared intentions. If you know your card games, chimpanzees are playing poker, humans are playing bridge.

Our discussion of human uniqueness on Logarithmic History has been frustratingly short on specific dates. But human sclera are probably a fairly simple trait genetically, and we may soon enough discover the genes involved and even tell how long ago they mutated.

Learn This One Weird Trick … (Part One)

… that humans use, and now you can too!

There are people who think that human beings are nothing special. Sure (the argument goes) people have uniquely large brains. But all sorts of creatures have unique features. Elephants are the only animals with trunks. Tamarins and marmosets are the only primates that give birth to twins. Platypuses are the only venomous mammals. Spotted hyenas are the only mammals whose females sport pseudo-penises (through which they give birth!). And so on. If we could ask members of these species they’d claim that they’re the special ones.

But of course we can’t ask them, and in any case, this isn’t a very convincing argument. Human beings have an absolutely outsize impact on the Earth, and the advent of human beings looks like one of the major evolutionary transitions, comparable in importance to the origin of the eukaryotic cell or multicellular life. But even if we buy this, it still leaves open the question of whether there’s a key adaptation – a One Weird Trick – that accounts for the exceptional course of human evolution. Here are some candidates that being are being batted around these days:

1) The cognitive niche. The basic idea is at least as old as Aristotle, that human brings are defined by their capacity for Reason. A modern version of this is advocated by evolutionary psychologist John Tooby and cognitive scientist Steven Pinker. Pinker in particular has elaborated the argument that humans are uniquely adapted to acquire and share knowledge, by virtue of a suite of cognitive, social, and linguistic adaptations. We’ve already touched on several aspects of this: Human beings seem to have taken the capacity for thinking about physical space and retooled it for thinking about the abstract cognitive space of possession – a social relationship. (Other abstract cognitive spaces include kinship, time, and change-of-state.) And humans seem to harness the machinery for processing the sounds of interacting solid objects in creating major categories of phonemes. For a more complete exposition, here’s an academic article by Pinker, and a talk on youtube.

2) Culture. Rob Boyd and Pete Richerson, who’ve done a lot of mathematical modeling of cultural evolution, are skeptical about the “cognitive niche” argument. Too much culture, they argue, is things that have been learned by trial-and-error, and are passed on from one generation to the next without people understanding why they work. Boyd and Richerson appeal, as anthropologists have for generations, to the importance of culture. We mentioned earlier their argument that the frequency of climate change in the Ice Age was nicely calibrated to favor social learning rather than individual learning or instinct. Joseph Henrich provides a recent defense of the importance of culture. Contra Pinker, he thinks humans often don’t have a good cause-and-effect understanding of the things they do, but depend heavily on imitation and the accumulated wisdom of the elders.

Coming up: Part Two. Recursion and Shared Intentionality

African geneses: Bushmen

271-257 thousand years ago

You’ve probably run into some version of the factoid that there is more genetic variation in Sub-Saharan Africa than in all the rest of the world. This assertion has to be handled with care. It doesn’t necessarily apply to genes that have been under strong diverging selection pressures on different continents. Consider skin pigmentation: there is not more variation inside Africa than outside it in skin color, or genes for skin color. Obviously. Likewise for hair form. But it’s true for neutral genetic variation, which is most genetic variation.

The simplest way to account for the broad Africa/non-Africa distinction would be to assume a large homogenous founder population in Africa, with a smallish number of people leaving Africa and going through a genetic bottleneck, thereby reducing their genetic variation. But recently we’ve been learning that the African situation is more complicated. Specifically, there used to be a lot of genetic differentiation between different regions within Africa. Recent population movements have smoothed out some of that variation, but recent work on ancient DNA has been bringing this more variegated past to light.

A case in point: the latest data imply that the Bushmen of Southern Africa separated from other African populations (East African, West African) around 260,000 years ago (at least), long before the major Out Of Africa venture by modern humans. What’s more, the very latest data imply that the Bushmen have received outside genetic input pretty recently, in the last 1-2 thousand years. This admixture, 9-22% of the ancestry of modern Bushmen, is absent from a 2,000 year old skeleton form Ballito Bay, South Africa.

The intruding population were probably pastoralists whose livestock, and a fraction of their genes, ultimately derived from the Near East. Another fraction of their genes originated in the Sahel or East Africa. And they probably spoke a language in the Nilo-Saharan or Afro-Asiatic family. These language families pop up as a substrate in East Africa, although largely overlain by the later expansion of Bantu speakers.

One implication: Bushman groups like the !Kung have often been presented as models for our Pleistocene hunting and gathering ancestors. Yet the most recent findings imply that there has been substantial interaction, including gene flow, between Bushmen and non-hunter-gatherers for some time.

A relevant result from twentieth century anthropology: when Nancy Howell did her classic work on the demography of the Dobe !Kung Bushmen, she found that, when you look at female genealogies, the Dobe !Kung look like a growing population, but when you look at male genealogies, they look like a shrinking population. There’s no contradiction here: the women, but not the men, in the population were sometimes having children by outsiders, neighboring pastoralists. The pastoralists in question were Bantu, having arrived in the last few centuries, but the latest genetic data imply that something similar was going long before the Bantu showed up. Since it’s not clear what effect this subaltern sexual status might have had on Bushman social organization, the social life of historic Bushmen may not be a good model for hunter-gatherer life before agriculture.

Here’s the article on Ballito Bay Boy.

And a recent review article from Nature

And assorted recent blog posts from Razib Khan, on the ancient Bushman split, and more recent African prehistory.

African geneses

Our picture of human evolution in Africa around 300 thousand years ago has changed dramatically in just the last year.

brokenhillHere’s something we already knew. This skull was found at Broken Hill, Zambia, in 1921, He (yes, “he,” he’s probably male) is sometimes known as Rhodesian Man. He looks like he’s a step away from Homo erectus, but not quite Homo sapiens. He’s heavily built, with massive brow ridges. (He looks like he could pass the “pencil test” for erectus: you could rest a pencil on those ridges. Of course, seriously, this isn’t enough to define a species.)  But he’s got a flat face and relatively large brain. He could be significantly younger than 300,000 years ago.

jebel irhoudBut now Rhodesian Man is bracketed both geographically and evolutionarily by some new finds. From Jebel Irhoud, Morocco, around 315 thousand years ago, come these skulls, which are more unequivocally Homo sapiens. pushing the fossil record of our species back 100 thousand years. The skull is still archaic ­– elongated rather than globular like a modern human – but the face is now tucked under the skull, as it is with us. The brow ridges are not as pronounced as with Rhodesian man, although still heavy for modern Homo sapiens.

naledi.jpgAnd we now have dates for Homo naledi, from South Africa, of 335-236 thousand years ago. This recently discovered species had a tiny brain, and may have been adapted for climbing trees, but still makes it into genus Homo based on other features (teeth and jaws, lower skeleton). The initial guess from a lot of folks was that this was a very early member of our genus, somewhere around early Homo erectus or earlier. But instead, Homo naledi looks to have been around at the same time as early Homo sapiens.

In other words, Africa 300,000 years ago was home to an impressive variety of humans – archaic Homo sapiens in Morocco, near relations in Zambia, and barely-humans in South Africa.

Hits, slides, and rings

Part of the challenge of language is coming up with some way to distinguish thousands or tens of thousands of words from one another. It would be hard to come up with that many unique sounds. What human languages do instead is to come up with phonemes and rules for stringing phonemes together into syllables, and then create words by arbitrarily pairing up one syllable, or a few, with a meaning. Phonemes are the individual sounds of a language, roughly comparable to individual letters. There are about forty phonemes in most dialects of English. (English spelling does a pretty sloppy job of matching up phonemes and letters. Finnish comes close to one phoneme per letter.)

Often in evolution organisms don’t solve new problems from scratch, but instead harness preexisting adaptations. I argued earlier that the abstract “space” of possession (“The Crampden estate went to Reginald.”) may have developed by harnessing preexisting concepts of physical space. And our abilities to recognize speech sounds may harness our preexisting capacities for recognizing the sounds of solid objects interacting. At least that’s the argument of a recent book by Mark Changizi, Harnessed: How Language and Music Mimicked Nature and Transformed Ape to Man.

Changizi notes that even though we’re mostly not aware of it, we’re very good at using our hearing to keep track of what’s going on in our physical surroundings. For example, people easily recognize the difference between someone going upstairs and someone going downstairs, and we’re pretty good at recognizing individuals by their treads. The sounds that solid objects make can be broadly categorized as hits, slides, and rings. Hits: one object collides with another and sends out a sharp burst of sound. Slides: an object scrapes against another and sends out a more extended sound. Rings: an object reverberates after a collision. Changizi argues that these correspond to the major categories of phonemes.

  • Hits = plosives, like p b t g k
  • Slides = fricatives, like s sh th f v z
  • Rings = sonorants, including sonorant consonants, like l r y w m n, and vowels

These are not the only sounds we can make with our mouths. We can do barks and pops and farts and so on. But our auditory systems are especially cued into solid object physics, so when we try to come up with easy-to-distinguish phonemes, that’s what we focus on. And a lot of rules about how phonemes hook up also follow from this principle – for example hits followed by rings are more common than the reverse.

There’s surely more going on with speech sounds than Changizi allows for. But if imitating nature is not the whole story of phonemes, it may at least be where they got started.

Later on when we talk about writing systems, we’ll see there’s a similar argument about how these are tuned to tickle our primate visual systems.