Genghis Khan notwithstanding. 
Note that random evolutionary variation in brain size amongst all species will always mean that the average brain size is increasingly larger over time, because there is a fixed lower limit (no brain) but no fixed upper limit on the size that brains can attain. Given that increased intelligence is sometimes an evolutionary advantage that outweighs the many evolutionary drawbacks of a large brain (e.g it sucks up huge amounts of your body’s resources, especially during development), and that this is normally a function of comparative intelligence (predators often benefit from being smarter than their prey), increasing intelligence over time is an expected outcome of random variation rather than a preferred evolutionary trend.
Large human brains may have originally been an accidental side effect of the mutation for retention of other fetal characteristics such as hairlessness that provided an immediate survival benefit. Once the larger brain was there, the increased intelligence it made possible became an added survival benefit in a primate social group environment.
We’re just another experimental niche that evolution has tossed out there, and we been doing good for a couple hundred thousand years, but who knows how we’ll do long term?
You got your cockroaches. Kinda dumb; great reproducers; very adaptable. Any give one is pretty expendable. Their niche has been successful for hundreds of millions of years.
You got your crocodiles. Kinda dumb. Tough guys. Been working their niche for a long time, too.
We’re the experiment in “intelligent but high maintenance weaklings.” Our babies take a long time to grow up. Our society is complex. Our reproduction is slow. Our physical ability lets us be the jack of all trades, with good fine motor skills, but a chimp half our size can beat the crap out of us, and we croak with pretty minimal exposure to the elements compared with some of our competitors.
So far, it’s a surprisingly successful niche, so it must be that the advantage of intelligence outweighs our high maintenance and lets us successfully reproduce. It also lets us take advantage of the pretty cool physical attributes we have–spectacular jack of all trade-ness: fine motor skills; arms and hands that can swing clubs; etc etc. However the ultimate irony might be that we get smart enough for our behaviour to affect the whole world and accidentally bump ourselves–or everything–off.
Thanks – I was unaware of this book, despite liking Steven Pinker’s work.
The bottom line is we really don’t know. There is a very strong reason NOT to grow big brains, which is that they’re terribly expensive in terms of energy. Another is that the big heads cause problems at birth (which is probably why we’re born unusually helpless, with much brain development happening after birth.)
And yes, while primates certainly had been growing bigger brains for many millions of years, the hominid line made a huge leap in that over just the last 2 or 3 million.
Greater intelligence leads to quicker adaptation to changing environments, because it allows cultural transmission of benefits rather than merely genetic transmission. There’s good evidence for our ancestors being, at different times, semi-aquatic, arboreal, and most recently creatures of the plains. Climate varied dramatically before the advent of agriculture. (In fact, climate has been remarkably stable in the last 10K years, which may be why it didn’t happen – or didn’t last – earlier.) But there’s the chicken-egg problem with that reason.
Some scientists think that a big factor was competition for mates, possibly coupled with developing linguistic ability. Bigger brains -> smoother talkers? Of course, this goes hand in hand with what Der Trihs says about the “Machiavellian theory”.
There is reinforcing feedback, such as mentioned above, tools allowing more and better diet, allowing more brain growth. (Development of human-like intelligence would be unlikely for a vegetarian species, due to the high caloric requirements.)
Walking upright and freeing the hands for things like tool use was certainly a factor. The question is why did upright walking evolve? It’s quite old, relatively; our brains were big for primates at the time, but small compared to even Homo Erectus; tiny compared to Homo Sapiens.
We’re not even sure how far back mastery of fire went. We know it’s at least 250K years, and probably at most 2 million. In addition to the ways in which fire is important, it also greatly extends the types of foods we can eat, essentially externalizing our digestion. There are a lot of natural (non-domesticated) roots and pulses that we can only eat after being cooked.
The language thing is also a big debating point. Did we grow big brains to handle language, or did the big brains allow language? Both, obviously, but the scientists who argue these things have a number of specific points in which the two differ.
Yeah, well, that’s what it really was. No doubt!
Good point, but probably not, due to the huge energy cost of big brains.
Technology is destabilizing. The rate of development of more unpredictable things happens faster and faster. My guess is, we’re toast already, on the evolutionary timescale. Does anyone think our species will survive even another 100K years? As a meliorist, I like to make the best of it and try to enjoy the ride.
If we do survive that long, we wouldn’t recognize our descendants.
Our pre-Homo ancestors’ brains were pretty much the same size as those of the other great apes. Well, we assume that by comparison to what they are today.
Not sure why technology is considered “destablizing”. But it’s unlikely H. sapiens will die out in 100K yeas unless the entire planet is destroyed. We’re pretty well spread out so as to avoid a mass extinction event.
We look the same as we did 100k years ago, so I don’t see why not. The only reason we might look radically different might be genetic engineering.
Remember, it’s a feedback loop. The ones who figure out that they can take the big stick with them, since they have hands, may survive better. Then, the ones who have the forethought to collect a pointy stick to take when they are at hand, before there is danger, are better survivors. The ones who understand the grunts and hand gestures that mean, Og,you go left and Grog, you go right - will eat better. The ones who figure out that they can sharpen a bone or stoneand take it with them to scrape a bit more flesh off the bones - live better., And so on.
It’s not just size, but complexity that requires a significant amount of food to simply maintain our brains. (One item I recall said 1/3 of out food goes to keep the brain working).
Remember, the limitation on a lot of evolution is that while a big brain or some other attribute may be “nice to have”, if it means the individual is more susceptible to starvation in lean times it is not completely useful. (Also a reason for physical size limits). There is only so much smarts you need to pick fruit in a tree. You don’t need to sneak up on it, or work in groups. Screaming an alert that can be heard half a mile away is all you need for cooperative defence.
Wolves, for example, have a reputation for “smart” and so instinctively (?) can cooperatively hunt much larger prey in packs.
However, the Machiavelli Theory has a limitation, that until there is large, organized fighting forces, any single human can be taken down by 2 or 3 others with weapons no matter how smart. With throwable pointy sticks, they do not even have to be bigger or faster. It seems to be a situaton better suited to agricultural times than small villages.
The “women as homemakers” is a logical evolutionary path because for the first year or two after birth a woman needs to feed her child; there’s a limit to how far she can stray. For a few months beforehand, too, endurance runner hunting is not an optimal activity. However, “home-maker” activities and gathering as much as hunting can benefit from planning, fine motor skills, and tool-making.
Maybe one of the big unsung advances not mentioned much is food preservation. Smoked meats and fish, sun-dried meat (Indian pemmican) etc - the ability to convert hunting and gathering into a longer-term food plan was a great leap forward. The brains that allowed us to figure that out - evolutionary advantage.
Will we survive? I think we will, but the stabilized hi-tech world will look a lot different from today. For one thing, modern economics makes it uneconomical and unnecessary (so, undesirable) to have children. Many countries are already on the raod to smaller populations, an oddity when everyone screams about overpopulation. Russia, Japan, Europe in general, and even one-child-each-China are well on the way to a 2050 demographic crash. Technoogy threatens to do the same jobs as before with a lot less energy. Take the lowly flashlight - or torch - as an example. When’s the last time you got 10 hours’ service for an incandescent bulb from 3 AA batteries? Autos in the 60’s we lucky to get gas mileage mpg in the teens. Today, it’s in the 40’s or better with hybrid, battery, and other magic tech “just around the corner”. Expensively smelted copper wires replaced with cheap glass fibre. And so on, but that’s not this thread…
It’s not clear to me that our average intelligence will change much. My general impression is that the less intelligent segment of our species generally has more offspring than the highest-intellect subset.
It’s my impression also that mating behaviour tends to fall along intellect classes more than any other single determinant, so I’d be interested to see in 100,000 years if we’ve diverged into two reasonably distinct clades.
I don’t think we’ll get there, though. We’re gonna figure out how to off ourselves accidentally–or, at least, holocaust ourselves back into the savanna. Plus, over 100,000 more years the chance of a natural disaster increases greatly.
John Mace…for some reason I was thinking we are bigger than we have been, smarter than we have been, and have better boobs–and that’s just the last few hundred years. What’s the evidence we haven’t done much evolving for a hundred thousand years?
I’m gonna evolve me some Eloi-eating teeth.
I didn’t say we haven’t done any evolving. But a person from 100k years ago would not be “unrecognizable” today and so I see no reason that a person 100k years hence would be. That was what I was responding to.
They’d probably need a shave.
Not to mention some deodorant!
Hmmm…
Considering that heavy beards seem to be a European adaption, many African and Asiatic/American Indian branches of the human tree do not seem to grow excessive facial hair - maybe not. Definitely, some grooming would be required.
There’s an interesting side topic… How and when did uncontrolled unlimited hair growth evolve? Presumably late enough in our tool-making days (or fire?) that haircuts were not more trouble than they were worth? (Does any other species display unlimited hair growth?)