What is the most important human adaptation?

Human infants require more care than they should, if we form our expectations based on closely related species (apes, and more generally, Old World simian primates). It has been said that humans are born three months early. This is not accurate. It was thought that our body size predicted a 12 month gestation, and some suggested that Neanderthals would have had such, but this research conclusion has been set aside based on new analysis. But it is still true that developmentally, human children do not reach a stage of development that allows some degree of self care for a very long time compared to apes. The actual sequence of development is not directly comparable: It is not the case that after a certain amount of time humans reach a specific stage reached earlier in the lifecycle by Chimpanzees, as the differences are more complicated than that. For the present purposes, we can characterize the human condition for early development like this: Human babies are more helpless in more ways and for longer than comparable ape babies.

Later in life, humans have a longer period of what might be called pre-adolescence than they "should" based on comparisons with related species. Some have characterized this as the insertion of a number of extra years of development. It could also be characterized as a period of time-lengthened development. Neither is perfectly accurate. One way to characterize the human condition for this period is this: From some time several months after birth through about the age of five or six (or more) humans engage in developmental activities not seen (or not as extensive or intensive) in other apes, during which humans learn a number of important things and engage in a number of neural developmental processes.

It is during this period that humans develop their knowledge of the kinship systems they will live with for the rest of their lives. Western populations tend to have poorly developed kinship systems, so this is easy to overlook, but virtually all other human cultures have complex and pragmatically significant kinship systems, and it is easy to observe children becoming aware of them and learning how to engage in them during this time. It is during this time that human children develop gender identity and gender roles appropriate to their society. They may learn class, caste, or ethnic roles as well. They start to learn the basics of the things they will need later in life, and what they learn is based entirely on what their society or culture requires: Being a blacksmith, a forager, a western/professional, whatever.

Most significantly, it is during this period that the child learns to use human language, a trait that is absent from our most closely related species.

Mel Konner, if I recall correctly, suggested the use of the term "childhood" as the period of development in which humans engage that is absent from the apes. (If he did not suggest that, he certainly popularized it with his documentary series called "childhood" and accompanying text.) The word "childhood" existed previously, of course. The term was suggested for use as the technical term referring to the inserted extra five years or so of development. Primates have a juvenile stage followed by the transition to sexual maturity, but humans have a pre-juvenile stage as well. This model can be rather clumsy, but suffice it to say that human young are doing something quantitatively and qualitatively different than ape young.

Primates tend to learn much of their ultimate adult behavior from the other primates with whom they live and by interaction with their natural environment, and this allows for certain things to happen, such as the development of behaviors that would be difficult or impossible to program genetically. This is a trait found widely in mammals and birds, but more so in some groups, including primates. It is even more true of the apes than of other primates, and indeed, apes have long periods of parent (mother) - offspring association, and are observed to engage in long bouts of learning and, remarkably, active teaching. Humans take this ape characteristic to a proverbial "order of magnitude" greater. One result of human hyper-extended and hyper-intensified child-age learning is the ability of human cultures to adapt (specialize) in a wider range of habitat exploitation strategies (lifeways) than otherwise possible. Indeed, the genetically coded behaviors that may well be present in primates (innate fear of certain things, certain aspects of territorial competition, sexual interaction, etc.) are often repressed or re-programmed in humans via culture. An interesting, though trivial, example is Heavy Metal. Heavy metal is a cultural manifestation (a "subculture"?) in which human participants revel in the instantiation of symbols almost all of which represent the repulsive, the dangerous, or the adaptively scary: Blood, predators, spiders, snakes, misplaced umlauts, and sharp things. That which we might reasonably guess would be genetically programmed into our beings is dragged out and made normal. This sort of thing proves that culture is capable of "overriding biology" (though that presumed relationship is often a falsehood) and suggests that human behavior in general may be primarily culturally coded rather than genetically coded. After all, culture is a powerful and rich source of information that can be passed on from generation to generation like genes, but altered in ways not possible with genes. One would expect selection to favor culturally mediated traits over genetically mediated traits.

And that may be our most important adaptation.


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It has been said that humans are born three months early. This is not accurate. It was thought that our body size predicted a 12 month gestation, and some suggested that Neanderthals would have had such, but this research conclusion has been set aside based on new analysis.

I had gotten the impression that this generalization was based on comparative fetal development: that human babies take three months to reach the physical state of other primates at birth (in terms of nerves, musculature, skull hardness, etc).

This was described as the necessary trade-off for giving birth to large-brained offspring through a bipedal pelvic structure, when the brain size evolved very rapidly (compared to most anatomical changes). Hypothetically, had our ancestors not worked out a fairly successful practice of midwifery/obstetrics, in X thousand more generations our species would become much wider-hipped (and possibly longer-gestating), by the process of killing off narrow-bodied women and their offspring.

So what's been disproven (izzat a word?) about this model?

By Pierce R. Butler (not verified) on 22 Oct 2010 #permalink

I think that the most important human adaptation is the neurodevelopmental trade-offs that a narrow maternal pelvis forced humans to have. Because the maternal pelvis is narrow, and so limits the size of the brain at birth, it limits the structures of that brain that can be encoded during proliferation and differentiation in utero. It limits what types of thinking that brain can be optimized to do.


I think this allowed humans to develop greater specialization of individual abilities and greater division of labor.

With division of labor, not everyone needs to be skilled at every task. Some can be highly skilled, and some can be hyper skilled in narrow fields. The products of the hyper skilled individuals can be used by everyone, so the whole group can benefit from the products of each hyper skilled individual in the particular and narrow field where they are hyper skilled.

I think that the most important human adaptation was not dying and continuing to reproduce. Lol!

Greg, this was very thoughtfully presented and I tend to agree, although I am not a genetic scientist. I'm speaking from the perspective of anthropology and sociology.

We live in cultures complex enough to objectify the cultural significance of something like misplaced umlauts; it should not surprise anyone that it takes longer to develop. (And that made me lol in public, but is was very much to the point.) It's my contention there is nothing we call human nature not addressed in some ways by cultures; even divergence from the central memes proceeds in reference to the original.

Another thing I wanted to add is that the fairly common meme comparing human early development with other species is certainly useful in an evolutionary biological context, but describing it as too long, or some other characterization implying that human development is defective in some way, just does not follow. I might as well point out that I am really, really old...in dog years. It's human development, not bonobo development. It may be clumsy or inefficient in some senses, but the processes result in us, and if it had evolved differently you and I would almost certainly not be talking about it here and now.

/end pet peeve

Nice post.

Nice post, Greg. I thought you were going somewhere else, though. A recent report in the Guardian says that someone has published a paper saying that the most important invention for humans was the baby sling because it enabled babies to be carried and the consequent attention they shared with their mothers (carriers) led to enlarged brains. And this was invented 2.2 million years ago. The evidence? The hominin brain showed its first (of two) major brain expansions 2.2 Million years ago. This is obviously circular.

Nevertheless, the argument that infant carrying impacted hominin cognition was the foundation of the argument that Noble and I produced 21 years ago. The steps were that bipedalism made carrying necessary, and hairlessness made it obligatory. The dating of the first of these is not (much) in dispute, the dating of the second is agreed but not demonstrated. So obligatory infant carrying must indeed have been around 2.2 million years ago (with or without slings). And the impact was probably immediately observable in the amount of "encoding" in the brain outside the womb. This, we suggested, is the fundamental human adaptation.

Problem is that the timing of the apparently delayed brain growth (relative to chimpanzees) is difficult to date. There are actually two candidate dates--the early brain increase and the second brain increase about 400 thousand years ago. Arguably this also was a time of important behavioural changes that could be said to be consequent on infant learning.

I discuss some of these issues in my paper: Davidson, I. (2007), ''As large as you need and as small as you can'--implications of the brain size of Homo floresiensis', in A. Schalley and D. Khlentzos (eds.), Mental states: evolution, function, nature (Amsterdam: John Benjamins), 35-42.

This can be found on my site: http://une-au.academia.edu/IainDavidson

Ian: I hope everyone goes and checks out your links.

I would not think that the baby sling is a different adaptation than altriciality. The "extended development" can be seen as a single big blob of an adaptation but it may well be multiple things, with multiple steps at distinctly different times. (Or not.) Most people would argue that the eye is a great adaptation, but it isn't. It's a whole shitload of adaptations.

I should also point out, and I'll address this in more detail later, that what I'm saying here is not groundbreaking or new. Rather, some version of this is what everyone in the biz believes to some extent, and it is something that has not been reiterated on this blog for a while. We have been arguing about genetic vs. cultural adaptations, and I'm taking heat from people who really know very nothing about this sort of thing, for assuming that most aspects of most human behaviors are not mostly genetic. But, when we look at humans, it is reasonable to say that one of our most important adaptations is the non-genetic or non hardwired nature of our behaviors. We should be surprised to see shopping for shoes or watching football or making umlauts on things as variable across our species in a way that maps underlying allelic variation!

That would be an umlaut of chës and fïn härbes presumably
Indeed you are deeply into a fight about genetics versus developmental (ontogenetic) change. Amd that is the issue about secondary altriciality. Big problem, as you know, is not only the extent of ontogenetic influences on aspects of language and cognition (separately or together). I would think that ontogeny is winning at the momentâhelped by a little local trouble that has emerged about the state of the evidence for non human primate cognitive abilities. But the other issue is whether altriciality and the so-called secondary altriciality can be identified in the archaeological record, and indeed what the stimuli for secondary altriciality might have been. It is not obvious to me how the advantages of secondary altriciality could simply lead to its emergence. But maybe that needs more exploration than I can do on a sunny Saturday morning with shopping to do and lawns to be mowed.

When reading this article, I was really fascinated. Although everything doesnât make sense to me exactly (being that Iâm still a student in high school), I did pick up on some key points. This isnât a topic that crosses my mind every day but when reading and analyzing, I could remember learning about this (although not as in-depth). Is there any physical adaptation that humans have gained over the mast thousands/ millions of years? I would have to agree with Greg in this article. I believe that a lot of the things we think and do are a source of âcultural manifestationâ. Our culture has a giant impact on everything we do and say. Very often, this leads us down a counterproductive route or to us making bad decisions.

@Pierce, the thing about selection that matters here is that we only think people who walk upright and who are smart are sexy. So rather than develop wider hips (which compromise bipedalism) or smaller heads (the brain thing) we went with preterm deliveries with corresponding neoteny and a spectacularly high loss rate for pregnancy and delivery. Lifetime maternal mortality runs at one in seven in some countries today, with neonatal loss rates of one in seven and maternal loss rates of one in one hundred per pregnancy. Modern obstetrics does such a good job that those loss rates are nigh invisible in industrialized countries. But there's no reason we couldn't have selected ourselves into extinction absent the invention of assisted deliveries.

One possible way to drive secondary altriciality might be that caretaking for our primary neoteny requires longer education in childhood -- to develop the sorts of skillsets that enable cultural support for complicated deliveries, for a mother/baby pair who can't forage enough to feed themselves, etc. Greg/ Iain, I can't remember enough of my Hrdy etc. to accurately report the state of the research here -- is this a reasonable possibility?

A bigger question, which I've never seen discussed scientifically, is how human female sexuality could have evolved, considering that it makes delivery even more difficult.

And I've never seen anyone rationally debunk the quack claim that it makes delivery easier.