Friday 18 May 2018

The impacts of anthropocentrism on our thinking about evolution

The impacts of anthropocentrism on thinking about evolution

In evolutionary biology, one of the big myths we are often tasked with dispelling is that that the traits which seem like obvious indicators of success to us are adaptive in the evolutionary sense. I call this an anthropocentric interpretation of evolutionary theory. For example, people have asked me, if evolution leads to survival of the fittest, why aren't humans getting smarter as a species? While the cynic in me wants to respond in the immortal words of Harvey Danger "...that only stupid people are breeding...", and there is an element of truth to this, the question calls for a much more detailed examination of the misconceptions behind the question.

There are actually several assumptions built-in to this question that are either universally false, or at least wrong most of the time. They are: (1) that the human (anthropocentric) definition of success = the evolutionary definition of fitness; (2) that the evolution of humans (and presumably other large vertebrates) is easily measurable over time-scales that are relevant to modern science; and (3) that past selective forces = current selective forces.

Before I explain further, let's re-examine the central tenets of evolution by natural selection:

- More individuals are produced each generation than can survive
- Within populations, individuals vary in their phenotypic traits, and this variation is heritable
- Individuals with beneficial traits are more likely to survive than those with detrimental traits

The first assumption is wrong because for a trait to be considered evolutionarily adaptive (beneficial), it must demonstrably be selected for, or be selected against less than alternative traits. In the context of human evolution, this means that for intelligence to be an adaptive trait, more intelligent people should not only be more capable of gathering resources (e.g., land, wealth, etc.), but also have more mates and produce more children than less intelligent people. Both parts are pretty soundly refuted by scientific research. Once you factor out education level, inheritance, and other influences, most smart people are no better at accumulating wealth than most dumb people.1 In addition, smart people (more specifically, those with high IQ scores) have been shown to produce fewer offspring than dumb ones2. So not only is being smart not an evolutionary advantage, being "dumb" may confer a slight advantage, if differential reproductive output is the primary measure of success.

However, such research also assumes that (1) people with high and low IQ's are on equal footing in other ways, and (2) that our data on IQ and reproductive rates in humans have been of consistently high quality over enough generations to allow for a reliable test, and (3) that the selective advantages have remained consistent over time. So for the time being, we'll have to let this rest with the statement that being smart is probably not an advantage in the evolutionary sense, although it may be in others.

The second assumption, that human evolution occurs over easily measurable time-scales, is in the category of "probably false". From examining fossil skulls of early homonids, anthropologists know that brain volume has increased at very coarse scales (i.e., over millions of years) from our earliest ancestors up until the last 10,000 years or so. Since then, our ancestors brain volume remained static or even declined slightly, although there is some evidence that this is linked to population growth and the impacts of the development of agriculture on human survival, with a slight increase occurring after the industrial revolution3. However, there is much more to human intelligence than brain size. Newer studies have shown that, at best, brain volume is only weakly correlated to intelligence; a much more effective measure is the number of synapses in a brain4, but this is pretty much impossible to measure without modern MRI techniques, so we're mostly outta luck on testing this question. In addition, recent research shows that for large anatomical changes to become widespread in a population, it can take up to a million years!5 Presumably, smaller changes can become widespread in a smaller amount of time, but to expect them to be evident in as short a time as we have had MRI scans for is clearly ridiculous. We actually don't (and probably can't) know whether the intelligence (in the modern sense meaning that which is measured by IQ or similar tests) has changed since our species was separated from our ancestors.

The third and final assumption, that current selective forces are the same as past ones, is almost certainly wrong. As mentioned above, brain volume changed a bit between hunter-gatherer humans and agricultural humans, but that's not the only thing that changed. Hunter-gatherer humans had far more robust skeletons overall. Although recent research6 has shown that this change is mainly just in the phenotype, rather than the genotype, of humans, it does illustrate a point: the environment in which early humans lived was very different than the one in which we now live. Different selective forces were at play. Consequently, the farthest back we should really be looking is the last 10,000 years, when agriculture was becoming more widely adopted. Post-agricultural humans are more anatomically similar to modern humans than pre-agricultural ones were, and therefore probably had more comparable selective forces at play. And I would argue that, realistically, we should be comparing no further back than the industrial revolution, when humans once again went through an abrupt transition towards increasingly sedentary lives.

So in summary, the answer to the question "why aren't humans evolving to be smarter", is that (1) intelligence does not currently seem to confer greater fitness (i.e., survival AND reproductive success), (2) actually testing this question would require brain scans or IQ tests of humans going back MUCH farther than we currently have, because evolution takes a long time, and (3) due to rapid technological changes, we are not operating under the same selective pressures as our human ancestors were, so even if we did have good information dating back a million years, it's unlikely the trend would continue to modern days uninterrupted.

In case this whole thing just went over your head, or the heads of the people you're attempting to explain it to, don't worry. I have a simpler way to explain it.

Remember when you were a teenager, and there were popular kids and jocks and nerds and Jesus freaks and goths and other easily identifiable subcultures in your school? Which ones do you think had the most sex over their lifetimes?  Probably jocks and preps, right? Which ones do you think used the least birth control?  Probably the Jesus freaks, right?

(More sex) + (less birth control) = more babies
 
and, when it comes to evolution,

more babies = greater fitness

This is assuming, of course, that the babies survive, as they probably would in today's world.

Let me leave the last words to Harvey Danger: https://www.youtube.com/watch?v=ZVOD5D4IArw