Tag Archives: technology

Accounting for brains

Why do humans have such big brains? Partly because we’re primates, and primates in general have big brains – not just big brains but an exceptional density of neurons, especially in big primates. But a recent article by González-Forero and Gardner offers some more specific ideas.

Before getting down to the article, a general reflection on statistics and methodology:

In many areas of science, you’ve got a lot of data and you want to sort out cause and effect. This happens in evolutionary biology, for example, when you want to determine what selective pressures have caused brains to evolve to different sizes. And it happens in medicine, when you want to find out what lifestyle choices generate what health problems. It also happens in social science and public policy, when you want to find out what programs generate what social outcomes. A common method in these cases is to use multivariate regression, looking for the strongest correlates of your dependent variable. This has its limits however. You often find that a lot of your variables are correlated with one another, and it’s hard to figure out what is cause and what’s effect.

So there’s been a lot of interest lately in a different approach, where you start out at the beginning with an explicit model of cause-and-effect pathways and use your data to estimate the strength of causal connections. An excellent popular introduction to this rapidly developing field comes from Judea Pearl, in The Book of Why: The New Science of Cause and Effect. Pearl makes the case here that statistics needs to move beyond pattern recognition, to testing causal models and counterfactual reasoning. Pearl sees counterfactual reasoning in particular as a human specialty, One Weird Trick that distinguishes humans from other creatures, and he is skeptical about current work in Artificial Intelligence, impressive as it is, that is mainly about pattern recognition.

Richard McElreath, commenting on González-Forero and Gardner, puts it this way:

“Automobile engineering can provide an analogy for studying this type of system. It would be difficult to understand racing-car design through regression analysis of how engine size varies depending on changes in other features, such as the mass and shape of the car. Instead, a model is needed that uses physical laws to predict optimal combinations of the variables under different criteria. Understanding brain evolution poses a similar challenge in that an organism’s features co-evolve under biological constraints.”

So turning to the article itself, what the authors do is to test an explicit model in which a developing organism has to allocate energy to growing a brain, growing a body, and reproducing. They ask what sorts of evolutionary challenges would lead to the particular combination of brain size, body size, and reproductive life history that we see in Homo sapiens. The challenges might be ecological (e.g. securing more food). They might be social (outwitting competitors). They might be solitary or cooperative (working with others to secure more food, or banding with others to defeat rival bands). Their conclusion: the best fit to their model comes when they assume that the evolution of big brains is 60% a result of individual ecological adaptation, 30% a result of cooperative ecological adaptation, and 10% a result of group-versus-group social adaptation. More specifically, what mostly drives the evolution of brain size in their model is that marginal returns to investing in ecological skills don’t decline as quickly for humans as for our close relatives. Spending extra years learning stuff continues to have a payoff for us, maybe because culture and language mean that there are a lot more useful tricks floating around to learn.

These results have to be considered pretty tentative at this point. Note however that they count strongly against the view that human brain evolution is mostly about being Machiavellian and outsmarting the other guys, although they do allow a modest role for inter-group competition. And they count against the view, advocated by Geoffrey Miller, that the human mind evolved as a sexual display, like the peacock’s tail. So it may be true that “sexual love … lays claim to half the powers and thoughts of the youngest portion of mankind” (Schopenhauer). But (at least according to González-Forero and Gardner), whatever the claims of love on our hearts, we owe our big brains to our work.


75 thousand years ago

The period between the time Homo sapiens leaves Africa 120 thousand years ago, and the time when H. sapiens spreads far and wide through Eurasia, replacing Neanderthals and others, 45 thousand years ago, sees episodes of increasing cultural complexity in Africa. One of these occurs at Blombos cave, at the southern tip of South Africa. There, over tens of thousands of years, people make a cultural great leap forward.
75 thousand years ago, we find that they produce finely crafted stone blades that are part of multi-part composite tools. They make shell ornaments.


And they etch ocher (a red stone useful as a dye, but not for tools).

Oddly though, this tradition doesn’t last. It’s over by 60 thousand years ago. It may be that people left as climate deteriorated. But Blombos cave is a reminder that cultural progress is not always a permanent thing. It looks like an early instance of Rise and Fall: a culture rises to new heights, and then falls back.

Quest for fire

1.043 million – 987 thousand years ago

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.

And here, if it’s your kind of thing, is Iron Maiden doing Quest for Fire.

My handaxe

1.23-1.17 million 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 just-published Mind in Motion: How Action Shapes Thought seems to make the argument at greater length; I’m looking forward to reading it. 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.


1.54-1.47 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:

Stonecraft as soulcraft

2.71-2.56 million years ago

Until recently the earliest known stone tools dated back to the Oldowan, 2.6 million years ago, although recently stone tools going back 700,000 years earlier were reported. Stone tool use may be a lot older than we thought.

We now know that tool making is not uniquely human. (For tool use in dinosaurs, see here.) But Oldowan tools – including choppers (below), pounders, and scrapers — go beyond anything chimpanzees, or other animals, do. Kanzi, a bonobo (pygmy chimpanzee, who was also taught to communicate with an artificial set of symbols) learned to use sharp stone flakes for cutting, but never mastered the art of striking a stone core at the proper angle to produce useful sharp flakes. Apparently australopithecines (or maybe early Homo or Kenyanthropus) had taken a step further by 2.6 million years ago (or earlier).


Early evolutionary theory developed in tandem with the Industrial Revolution and included an appreciation for the importance of manual labor. Darwin, in The Descent of Man, argued for the central role of toolmaking in human evolution, and, not surprisingly, the same point was echoed by Friedrich Engels in 1876, in his unfinished essay “The Part Played by Labor in the Transition from Ape to Man.” Engels was pushing back against the attitude in most traditional stratified societies that manual labor is low class, while symbolic labor (and/or wielding weapons) is high class.

For example the fingernails on this Chinese scholar advertised that he didn’t work with his hands.


Nowadays, a common complaint about the post-industrial economy is that so much education and employment revolves around pushing symbols around that manual labor is relatively devalued. The recent book Shopcraft as Soulcraft: An Inquiry into the Value of Work is a statement of this lament. Maybe today is a good time to celebrate the part played by labor in the transition from ape to man — by making something, or mending something.

But if food is more your thing, the next post will suggest a recipe.


Coals to Newcastle

320-304 million years ago

It seems like Gaia really went on a bender in the late Carboniferous, getting drunk on oxygen. By some estimates, the atmosphere was over 30% oxygen back then, compared to 21% today. Living things took advantage of the opportunity. Insects apparently face an upper limit in size because they rely on diffusion through tracheas instead of forced respiration through lungs to get oxygen into their bodies. With more oxygen in the air, this limit was raised. The Carboniferous saw dragonflies with a wingspan up to 70 centimeters, and body lengths up to 30 centimeters, comparable to a seagull.


This happened because plants were turning carbon dioxide into organic matter and free oxygen, and the organic matter was accumulating. With carbon dioxide being removed from the atmosphere, the late Carboniferous and subsequent early Permian saw a reduced greenhouse effect, and global cooling. This was another Ice Age, with ice caps around the southern pole.

A lot of organic carbon ended up being buried. Much of the world’s coal, especially high quality anthracite, has its origin in Carboniferous tropical forests. Western Europe and eastern North America lay in the tropics at the time, and got a particularly generous allotment of coal. Three hundred million years later this bounty would fuel the early Industrial Revolution. (Thanks partly to some of my Welsh ancestors, who helped dig it up back in the day.)

coal age