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. And see this post, for the importance of High Fidelity cultural transmission in the evolution of animal and human intelligence.

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 in 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 from 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 reproductive histories, the Dobe !Kung look like a growing population, but when you look at male reproductive histories, 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

African geneses

303 – 288 thousand years ago

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

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

530 thousand – 501 thousand years ago

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.

So even 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.

Speech sounds

Below are some reflections on language. There will be plenty more in days to come. For a science-fictional take on language, try Octavia Butler’s account of a world where language has disappeared, Speech Sounds. It’s one of her best. It won science fiction’s Hugo Award for best short story in 1984.

We’re now six months through the year 2018 at Logarithmic History. We raced through time at the rate of 754 million years a day on January 1. December 31 we’ll cover just one year (the year 2019) per day. Today, July 1, covers 29,037 years, from 531,725 to 502,689 years ago.

By today’s date, the universe is a lot more complicated than when we started. As we mentioned before, one of the major sources of complexity is the origin of new discrete combinatorial systems, made of small units that can be combined into larger units that have different properties than their constituents. Elementary particles are the first discrete combinatorial system to appear, already present in the early moments of the Big Bang. The different chemical elements are another major discrete combinatorial system. It took billions of years for enough heavy atoms, beyond hydrogen and helium, to accumulate from stellar explosions, allowing the complex chemistry and geology that we know on Earth. It may be that the paucity of heavy elements in the early Universe is what prevented earlier planetary systems from developing complex life.

With the origin of life comes another discrete combinatorial systems, or rather two connected systems: nucleotides strung together to make genes, which code for amino acids strung together to make proteins.

For the second half of the Logarithmic History year, we’ll be spending a lot of time looking at the consequences of another discrete combinatorial system: language. Or maybe, as with genes-and-proteins there are really two systems here: words strung into phrases and sentences, and concepts strung together into complex propositions in a Language of Thought.

The origin of modern human is one of the major transitions in evolution, comparable to the origin of eukaryotic cells, or of social insects. Language is crucial here: slime molds and ants organize high levels of cooperation, turning themselves into “superorganisms,” by secreting pheromones. Humans organize by secreting cosmologies.

Heidelberg and Bodo

By 600 thousand years ago we’re finding people who don’t fit comfortably into Homo erectus. A jawbone from around this time was unearthed in Germany, near Heidelberg, in 1907. Another find from the same period, often assigned to the same species, comes from Bodo, Ethiopia (below).

bodo

This guy clearly isn’t modern Homo sapiens, but his brain is starting to get out of the Homo erectus range (1200 cubic centimeters cranial capacity), and his browridge is a double arch, rather than an erectus-style straight bar. He’s also got cut marks on skull and face, from someone “defleshing” him. A respectful mortuary ritual, or did somebody really not like him?

The exact relationship of these guys to later humans has been unclear. A popular theory assigned both to an intermediate species, Homo heidelbergensis. However yesterday we reviewed very recent genetic modeling by Rogers and coworkers that suggests that a three-way split between Homo sapiens, Neanderthals, and Denisovans has already happened by this point, although the lineages haven’t had long to differentiate. So probably Heidelbergers in Europe are ancestral to Neanderthals (or at least closely related to their ancestors), while Bodo man is ancestral to our variety of Homo sapiens, or represents some kind of African side branch.

It’s a small world after all

595-563 thousand years ago

The story of human origins is partly a story of Big Things like The Taming of Fire and the The Dawn of Speech. But it’s also the story of some odd byways and quiddities. A nice introduction to some of these is Chip Walter’s book Thumbs, Toes, and Tears: And Other Traits That Make Us Human. (His more recent Last Ape Standing is good too.) Walters considers funny bits of anatomy like our unique big toes and thumbs, and funny bits of behavior like our habits of laughing, weeping, and kissing. Toes and thumbs fossilize, but behaviors can be hard to date, evolutionarily. Presumably these behaviors appeared sometime before modern humans evolved and spread, so let’s pick today’s date. It’s also hard to figure out the exact evolutionary rationale for some of these behaviors. Humor, for example, is not a simple phenomenon: intellectually appreciating a joke, actually finding it funny and enjoying it, and finally laughing, each involve separate areas of the brain.

Laughter, specifically, is a minor human oddity that sheds an interesting light on some big events in human evolution. Robert Provine, a leading laughter researcher, spells out the argument in “Curious Behavior: Yawning, Laughing, Hiccuping, and Beyond.” Chimpanzees have a kind of laugh, a modified vocalized panting synchronized with inhalation and exhalation. Presumably laughter first resulted when panting-during-play evolved into a play signal. But the short bursts of human laughter go further, having freed themselves from synchrony with the inhalation/exhalation cycle. Laughter, in other words, is just one instance of the more general phenomenon of humans having separate controls for vocalization and for respiration. Interestingly, the most prominent examples of complex vocalization – songbirds and some other birds, whales, bats, and humans – are all found in non-quadrupeds. In quadrupeds, breathing is tightly coupled with locomotion: lungs need to be full to stiffen the thorax when the forelimbs hit the ground. Giving up quadrupedalism seems to have allowed for an “adaptive release” in the evolution of vocal abilities in a number of unrelated lineages. So the study of laughter (and other vocalizations) suggests that two key human adaptations – bipedalism and spoken language – are more closely linked than one might have expected.

Another and overlapping set of human particularities involves facial expressions of the emotions. Darwin got a whole book out of this. He concluded (admittedly based on somewhat anecdotal evidence) that different emotional expressions are largely innate. It’s an interesting illustration of his ability to reason from small facts to large conclusions that he also drew a big conclusion about human evolution from this. In Darwin’s day, there were scientists who believed that different human races had evolved from very different prehuman progenitors: one prehuman species giving rise to Europeans, another to Africans, and so on. But Darwin reasoned that the very close similarity in facial expressions (and he had traveled a lot, and witnessed a lot of expressions in a lot of places) and the very similar emotional makeup of humans around the world was evidence that human populations shared a fairly recent common ancestry. Here as in several other cases, a mixture of close reasoning and sheer luck led Darwin to the correct conclusion about evolution long before there was much solid evidence.

Darwin’s work on emotions was neglected for most of the twentieth century by anthropologists favoring a blank slate view of human behavior, but was eventually largely vindicated by a number of researchers, notably Paul Ekman. There is now good evidence for six basic facially expressed emotions: Fear, Disgust, Joy, Anger, Sadness, and Surprise.

If you’re a movie watcher, this list may seem familiar. These emotions (all except for Surprise) are all depicted as little homunculi living inside the head of an 11 year old girl in the animated feature “Inside Out.” Somebody at Pixar Studios knows their Ekman.

insideout

So the sappy song is right: There is just one moon and one golden sun, and a smile means friendship to everyone.