(Picture from here.)
It’s hard to talk about human evolution.
Not because it’s not interesting or that there’s not an enormous amount of information about it. Humans have no obsession that can compare to the obsession they have about themselves. Consequently, almost any conclusion we tend to make about ourselves is tinged with wish fulfillment, private agendas, political ideology and narcissism.
For example, it’s a known fact that men’s brains are between 10-12% larger than women’s brain. That’s all I’m saying: it’s a fact. Does it say anything about relative fitness? No. Does it say anything about relative intelligence? No. Does it say anything about relative pay or political ideology between the sexes? No. Yet if you look for them you can find papers using this fact as a base for fairly wild claims. (See here for one involving SAT scores.)
Are women different from men? Of course– nobody but a fool would argue differently. What we argue about is what those differences mean. The context changes as new facts show up but the argument remains over generations. (As an aside one wonders why we have such an investment in judging our opposite sex so acutely.)
For men vs women you can substitute race, nationality, religion or anything else.
In my opinion all things biological must be investigated in the context of evolution. Heritage must be determined in all things. So let’s look at brain size differences in that spirit.
In the above example using the brain size difference to explain SAT score differences is backwards. First you have to determine what selection caused the size difference in brain size– maybe start with sex size differences in humans and determine how much of the brain size difference can be accounted just by that. Then, take the difference (if any) and see if the same differences show up in our closest cousins. That would help determine if the brain size difference derives from our heritage or is something we developed on our own. Hypotheses must be confronted with data. This data comes from here:
|Animal||E/Q||body weight kg||brain weight g||M/F Body % diff||M/F Brain % diff||Brain-Body diff|
E/Q is the encephalization quotient, the relationship between brain size and body size. As expected, humans have the highest E/Q, followed by chimps and then gorillas.
One way of analyzing this data might be to say the difference between body size difference and brain size difference is what’s significant here. We might even go so far as to drop the gorillas since they’re known for extreme sexual dimorphism. Or we could just say that the chimp and human show enough difference to believe the sexual brain size difference is real– it’s close the same value for humans and chimps– and that the sexual dimorphism in gorillas masks what would otherwise be a similar value. Further research might include looking and bonobos, orangutans, gibbons and baboons.
So we hypothesize that the brain size difference is real and is roughly 3% in chimps and humans. If so, the data suggests that it derives from the common heritage rather than anything uniquely human.
This does not disprove the hypothesis that brain size difference between men and women indicates some underlying difference in cognitive properties. Just because there’s an unexplained 3% brain difference in male and female brain sizes in both chimps and humans doesn’t mean it’s the same 3% of brain tissue. Even if that 3% was the same tissue it doesn’t mean that humans are using that extra bit of brain in the same way as chimps. But it does saddle those that subscribe to the brain size == intelligence hypothesis with the responsibility of actually proving it. They can’t just look at the size difference and say “See?”
Not to say I don’t think there might be differences in cognition between men and women. There might well be. But I use my words carefully here. I said differences. Not a qualitative better or worse. Often in our misplaced narcissism we instantly translate difference to better or worse. I would be completely unsurprised to find such interesting differences. For one thing women have historically undergone very different selection pressures than men. Women bear children– a very risky business. They have to undergo significant stress in process of pregnancy and tremendous nutrition stress during lactation– my grandmother used to say a “tooth for every child.” Men as hunter gatherers dealt with the risks of hunting. Much of the risk of war is born by men though women often bear the brunt of losing. There is also a tremendous strong pressure on how we get along– no offspring, no continuation of the species. Yet though the selection on women and men might be different they must share the same genome so sexual differences have to conduct a delicate dance between the cost of maintaining differences and the advantages of those differences.
But whatever those differences are they have nothing to do with SAT scores.
Where this gets really sticky, though, is not when there are obvious axes to grind, such as attempting to show one sex is less intelligent than the other, but when real changes actually show up. We know that there have been genetic changes in human beings in historical times. We need only look at the rise of lactose tolerance in human beings. This arose sometime in the last 7,000 years and appears to have occurred in populations whose ancestors that could support milk cattle.
Cultures can cause genetic changes by presenting boundaries to interbreeding or promoting specific characteristics. A really good example of culture cause selection is the history of Tay-Sachs disease among Ashkenazi Jews. This is not a pleasant story.
Tay-Sachs is a disease that results from a recessive mutation. Cell membranes have components called gangliosides. The mutation involves the break down of these gangliosides. When the mutation is present from both parents the gangliosides build up and there’s a progressive deterioration of nervous system function eventually causing death in early childhood.
There appears to be some protection against tuberculosis when the individual has only one copy of the mutation– analogous to the protection the sickle-cell anemia mutation gives against malaria.
The T-S mutation had a comparatively high presence in Ashkenazim prior to World War II. In Nazi Germany Jews were confined in ghettos, further reinforcing reproductive barriers. TB ran rampant through the ghettos forcing a selective pressure on the Ashkenazim: those with 1/2 the T-S mutation were more likely to survive which drove up the incidence of the mutation in the survivors to it’s now fairly high 11%.
We can perceive specific genetic changes like this. They’re small. They don’t affect the majority of behaviors and characteristics of the population save for those tragic couples who have T-S children. With modern genetic testing I suspect that mutation is going to disappear relatively quickly.
However, broader changes are harder to discern. Cultural changes can have a significant impact on genetic diversity and selection but such changes are ephemeral over time. And they have to be highly advantageous to spread over in a large population. Even the relatively simple lactose tolerance mutation has not swept over the world; it is still confined to specific genetic populations. In addition with lactase pills the advantage has disappeared.
We have to be willing to accept that we don’t know and making up bad science in service of what we think ought to be.
There is reproductive selection going on with human beings. I have my own ideas as to what they’re selecting for. Higher tolerance to crowding, for example. Quick perception of social situations. Advanced technological sophistication. Moving away from the ability to memorize large amounts of data to managing to remember data structure and location. Why keep something in your head that’s going to be obsolete in twenty minutes? Better to understand how to update that knowledge form an external source. But that might be just the whim of the moment. Who knows what the future will bring?
We know it’s going on. We can see it. We have to be willing to admit we don’t know what it means.