It is clear to see that in past 20 000 years, the environment in which humans live has undergone very significant change due to emergence of societies; the new environment may not be pushing us as hard, at least on the individual level.
I'm not an anthropologist, but one plausible explanation I can think of for the brain shrinkage is almost diametrically opposed to this. It's pretty well established that early agricultural societies placed more nutritional stress on their citizens than the hunter-gatherer lifestyle that preceded them; height and various other nutritional proxies consistently went downhill after the agricultural transition and in most places didn't make up the difference until the Renaissance or even later. Brains, as you say, are an energy-intensive piece of equipment; and agricultural productivity looks a lot less elastic with regard to intelligence than hunting or foraging. Put that together and you've got a pretty strong argument for negative selection pressure w.r.t brain size, at least until industrialization got rid of most nutrient constraints. I wouldn't even be too surprised if this was responsible for part of the Flynn effect, although there are cer...
My best guess is that it is the capacity to invent solutions on spot and think by ourselves, that we are losing. Before emergence of societies, the technological progress was severely limited by information loss. Any smart individual could massively improve fitness of the relevant genes by (re)inventing some basic, but extremely effective techniques, which he'd teach mostly to genetically related individuals. The technique would easy become lost, creating again an opportunity for intelligence to succeed - reinventing it.
Except most discoveries which might confer a decent amount of fitness - enough for fixation to have a chance - are rare. For example, Tasmania had a population of thousands, yet they lacked almost all technology, and couldn't even make fire (instead relying preserving existing flames); if anywhere someone would be inventing technology to help their kins, Tasmania should have seen such secret wiles. But no.
(This is part of a general argument against individual selection for innovation: innovation is too rare, and diffuses too rapidly to unrelated or barely-related people, to be an advantage for the individual - however excellent it is for the group.)
edit: plus from what i've read i'm not even sure they didn't have fire, in the first place.
I never said they didn't have fire; please read what I wrote.
You can't just go around dispelling advantages of big brains without providing any alternative explanation why big brains evolved.
Of course I can.
And besides, it's a very simple story: if big brains improve individual reproductive fitness by enabling innovations, then there need to be innovations. Evolution can't act on genotype which is never expressed in phenotype. In Tasmania, not only are there no innovations, there's actual loss of existing innovations. If you try to argue that the population base was too small, then that's even more damning: what kind of innovation-supporting gene can be selected for by Evolution when thousands of aborigines over many generations all fail to produce anything? Even if one aborigine did, how does that make up for thousands of his relatives/ancestors burning huge amounts of calories and protein on the innovation-capacity only one of them benefited from?
Combined with the observations about innovating being a public good (and group selection being rare to non-existent), this is pretty convincing evidence that big brains were not selected for their innovation, but for something else - the Machiavellian brain hypothesis seems like a good one.
Did the Australian Aborigines undergo similar brain shrinkage? If not, they would be good tests of any particular hypothesis of loss.
(The palaeolithic humans did not seem to do any really insane religious stuff)
Pure speculation, based on the misfiring heuristic that since stone age Europeans where not building cathedrals and where not writing up religious texts they might not have been that religious.
Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball.
Differences between the average brain sizes of currently existing populations are comparable.
Your hypothesis isn't worth much until you find a way to test it. Simply reasoning it out doesn't cut it.
I think humans aren't that special in this regard. There are plenty of other examples of domesticated species having smaller brains (Canis lupus familiaris for starters). And yes humans are animals and it would be pretty hard to argue that we aren't in fact domesticated. :)
If I had to guess I would say that our sense of smell and the part of the brain dedicated to making sense of that data may have decreased significantly precisely because of our domestication of dogs.
Going off some of the writing of anthropologist Peter Frost. I think a good case can be...
The notion that our brains just got more efficient and 'therefore' could shrink in size appears very shaky to me. This 'therefore' comes from fallacy of anthropomorphizing the evolution.
Up voted for taking evolution seriously when it tells us that it simply wants to maximize fitness and dosen't care about what we like.
I think you are right on our biases regarding this.
Hypothesis I just made up:
Drops in violence and changes in the kind of violence (yay arrows!) in the past 20 000 years have reduced the need for cognitive back ups as well as robust skulls since brain trauma is less common. Our ancestors may have had bigger brains but not have been much or any smarter because they literally got hit on the head more often.
The average size has been going down but the variation has also increased a lot (probably because humans can use culture to stratify by cognitive/physical phenotype). Lord Byron's skull was 2200g (which is downright unwieldy) and he was neurologically atypical. His daughter was more stable (the second X chromosome can offset deleterious stuff in the patrilineal one), but also wrote the first computer program in 1842. There is probably a correlation:
Family History of Psychiatric Disorders Shapes Intellectual Interests (Jan 2012)
...Students interested in p
This could also partly explain the Fermi paradox. May be difficult not to de-evolve too early, for a technological civilization to bloom.
No, but size correlates fairly strongly with intelligence, in both primates and humans: http://en.wikipedia.org/wiki/Neuroscience_and_intelligence#Brain_size
So the question becomes, why does this size decrease not decrease general intelligence, or if it left general intelligence alone, what capabilities did it affect? (Maybe visual working memory, given chimpanzees' superior capabilities in that regard.)
Related reading: http://www.gwern.net/Drug%20heuristics#modafinil
Anthropologist John Hawks (quoted in the Discover article) in this video (at the 9:23 mark) shows data on the shrinking human brain over 16000 years. On his display it looks to me like the scatter extrema for today are over twice as large as the decline in the linear regression line. The number of data points from 16000 years ago is not large.
The palaeolithic humans did not seem to do any really insane religious stuff
Why? The first thing I checked has one anthropologist speculating cannibalism might have occurred during the paleolithic for religious reasons, and on the whole doesn't look very encouraging.
The real argument against cannibalism seems to be easy transmission of infection, not held back by species boundary. If this risk is comparatively sufficiently low, I'd say not eating your fellow humans who died anyway when the food is scarce is a failure mode (famine seems to be convincing enough, and probably occurred often in the prehistoric past).
A further quote from the same paragraph, emphasis mine:
Nonetheless, it remains possible that Paleolithic societies never practiced cannibalism, and that the damage to recovered human bones was either the result of ritual post-mortem bone cleaning or predation by carnivores such as saber tooth cats, lions and hyenas.
Just for kicks, I might also assume the (contrarian?) position that cannibalism is by no means unconditionally "really insane," which seems to be what you're holding it out as an example of. Sure, it has its (ups and) downs, but I'm not on board for really insane. Killing someone à la Mayan human sacrifice seems to me crazier and more harmful than eating someone's body as a burial rite at a time when food may well be scarce.
That said, I agree with your thrust; namely, that we have no good reason to believe the paleolithic folks were anyhow significantly smarter or more moral than us.
From the article:
Some 30 animals have been domesticated, he notes, and in the process every one of them has lost brain volume—typically a 10 to 15 percent reduction compared with their wild progenitors.
A strong claim if true.
I found this book on google scholar and the parts of it I read supported this claim more than refuted it but were not so definitive and absolute.
Toward the end of the article, they give their theory - that aggressive tendencies were bread out when population density increased. The scenario they describe, is of people getting together to kill off the big hulking brute in their midst.
We became a domesticated species, and like other domesticated species, domestication came with a decrease in brain size.
They note that brain size has been increasing for the last 200 years, but attribute that to increasing nutrition.
As mentioned the environment plays a large part. My main point is, a more robust phenotype may have been selected for in harsher climates - thicker bones, larger skulls, larger brains. An example are Neanderthals - they became cold adapted, and therefore had a 'robust' phenotype. Robust hominins often have thickset skeletons and large heads - and therefore somewhat larger brains as a consequence.
The actual average size of the Neanderthal brain - was not significantly greater than modern humans. Also the Neanderthals had a different shaped skull - and a dif...
My best guess is that it is the capacity to invent solutions on spot and think by ourselves, that we are losing.
That sounds probably-correct.
Perhaps look into self domestication and the recent findings about bonobo self domestication.
The notion that our brains just got more efficient and 'therefore' could shrink in size appears very shaky to me. This 'therefore' comes from fallacy of anthropomorphizing the evolution. Evolution doesn't work to a goal of optimizing some sub-unit in the organism while preserving specifications, in the way that a team on an engineering project would.
Suppose that there were mutations which improved brain efficiency, but had other unfortunate side effects - these would be adaptive above a certain brain size threshold. We shouldn't of course presume that this was the case, but it's not implausible either.
As human population densities increased and complex societies formed, selection pressure for social skills increased, and social skills became more relevant than intelligence. Larger brains usually have fewer long-range connections but more local connections, and long-range connections enable the rapid processing required for socialising. People with autism tend to have larger brains than those without and females tend to have smaller brains than males, so an inverse correlation between brain size and social skills would not surprise me.
Hmm. If it's been going on for 20,000 years, then we have groups of humans living in something like ancestral conditions who've been isolated that long. The Sentinelese come to mind (~30,000 years of isolation from the rest of humanity). I can't offhand think of any ethical way to check this, though. Some isolated peoples in New Guinea might also qualify, but a surprising number of them are farmers and have been for a long time. Regardless, if you checked the average brain volume of people from this group (who haven't been effected by agriculture, and may ...
We are lacking a tennis-ball sized piece of our earlier brain (and it might even be God-shaped).
I'd bet against that. Civilizations seem to like gods.
: Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball.
This isn't that much actually differences in brain sizes between existing ethnic groups are comparable.
We are lacking a tennis-ball sized piece of our earlier brain (and it might even be God-shaped).
Could you clarify for me what this means, exactly? I mean the bit in parentheses in particular; I've heard the phrase "god-shaped hole" before but I'm not sure what relevance it has to the topic at hand. Are you postulating a claim that if we were smarter by the brain volume of a tennis ball, we would be more aware of God?
...The important question is - Did we lose any functionality since then? Are we dumber? Are we less sane in some way? (The palaeol
Is this result (brains are shrinking) really well-established? My first impulse is to defy the data...
The human brain volume has been shrinking over the past 20 000 years or so, after millions years of increase in volume. Not just the brain size, but the brain size relatively to body size as well. We are lacking a tennis-ball sized piece of our earlier brain (and it might even be God-shaped).
Brain is expensive in many ways: energy consumption, birth complications and locomotion impairment for females, lower survival of head impacts i'd guess. The damn thing along with supporting structures is heavy and awkwardly located, etc.
And the big brain can only be advantageous if it improves reproduction substantially, with larger brained individuals being sufficiently more successful at surviving and reproducing than smaller brained individuals, as to negate the above-mentioned cost.
That must have been the case through the evolution up to a couple tens thousands years ago, to produce the big brains that we have. It is clear to see that in past 20 000 years, the environment in which humans live has undergone very significant change due to emergence of societies; the new environment may not be pushing us as hard [in the direction of intelligence], at least on the individual level. [and may have been pushing us too hard for smaller brains, thanks Nornagest for making that point]
We were evolving ability to think, until it got just about to the point of being barely able - with great difficulty and many falls - to think useful thoughts. If we were species that were evolving flight, we'd be the species that could just barely fly, and recently flew over a river, entering new land. In the new land, everything is different. And our wings were shrinking at very rapid rate.
The important question is - Did we lose any functionality since then? Are we dumber? Are we less sane in some way? (The palaeolithic humans did not seem to do any really insane religious stuff)
The notion that our brains just got more efficient and 'therefore' could shrink in size appears very shaky to me. This 'therefore' comes from fallacy of anthropomorphizing the evolution. Evolution doesn't work to a goal of optimizing some sub-unit in the organism while preserving specifications, in the way that a team on an engineering project would.
The optimization could as well instead make brain even larger, if said improvement made larger brain pay off more. One would have to show that some improvement in brain efficiency has actually decreased advantage of big brains over small brains, to explain the smaller brains with them being more optimized.
The evolution optimizes the whole organism, not the brain, and there's very many of other factors that have changed at that specific time that may as well have decreased selection pressure towards intelligence or increased the costs.
In my opinion the sensible default hypothesis should be that we had a decrease in some functionality, and likely are still declining.
My best guess is that it is the capacity to invent solutions on spot and think by ourselves, that we are losing. Before emergence of societies, the technological progress was severely limited by information loss. Any smart individual could massively improve fitness of the relevant genes by (re)inventing some basic, but extremely effective techniques, which he'd teach mostly to genetically related individuals. The technique would easy become lost, creating again an opportunity for intelligence to succeed - reinventing it.
Even very simple invention requires massive search in the vast space of possibilities. Precisely the kind of task that one would expect to benefit from larger raw computational power.
edit:
Some clarification with regards to the need for innovation. In the long run, it is not enough to just do what you're taught. Teaching is a lossy process. You need to improve upon what was taught to you a little to make the tool as good as your ancestor made - you need minor innovation to merely preserve the tools - a little more innovation and you'll improve over time, a little less and you'll lose it over time. The little children have to figure out everything from a few clues; they don't download some braindump of the wisest elder to be able to speak, they essentially figure out an alien language - a very difficult task.