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Chimpanzees Have Quantitative Traits, Who Knew?
Credit: Schimpanse Zoo Leipzig, Thomas Lersch

Credit: Schimpanse Zoo Leipzig, Thomas Lersch

Some recent research has just been published with the title Chimpanzee Intelligence Is Heritable. My first thought honestly was “No shit? Of course.” My friend Jason Goldman has already done a very good write up at io9 if you want read about it and don’t have access to the paper. In commenting on the results Jason notes (and I agree with the general thrust here):

That isn’t a particularly surprising or novel statement on its own [that chimpanzee intelligence is heritable -Razib]. We already knew that genes have an important job when it comes to intelligence and cognition. But what’s useful is that we can assume chimpanzee intelligence isn’t influenced by factors like socioeconomic status, the quality of their school districts, or any of the dozens of other variables, both obvious and subtle, that influence human development. That means we can examine the “genetic” side of their intelligence more easily.

Of course chimpanzees vary in intelligence, and, that variation has a genetic component. Part of the issue here is human essentialism. Chimpanzees are less intelligent than the average human, and so are classed into a general category of the second-most-intelligent-ape, as if their variation is totally irrelevant (and for practical day to day purposes it is). Pound for pound chimpanzees are also much stronger than we are. But would anyone be surprised if chimps varied in strength as a function of their genes (controlled for sex)? I doubt it. The issue, if there is one, is that intelligence is perceived as the sine qua non of humanity.

Horseshoe crabs, evolutionary success!

Horseshoe crabs, evolutionary success!

Jason suggests that chimpanzees could serve to explore issues in relation to the development of intelligence and its dependence upon genes and environment. Perhaps, though I think if that is what you want to explore in animal models birds or outbred rodent lineages would be more cost effective. I’m pretty sure they’d exhibit heritable variation in general intelligence as well.

Though obviously there seems to be selection for larger brains in the primate lineage, and perhaps in chordates in general, over hundreds of millions of years, I think it’s a huge step (which I would dispute) to suggest that intelligence itself is evolutionarily favored over shorter time scales (i.e., one can perhaps argue evolutionary success accrues to the brain in a macroevolutionary sense, but far less in a microevolutionary scale of operation). I bet a lot of the evolutionary action is in what cognitive psychologists would term “domain specific cognitive capacities.” E.g., our ability to learn and speak language with complex syntax, which is a human universal. In contrast there may not be that much selection in a directional sense for “domain general cognition.” From a population genetic perspective this would explain why there’s so much heritable variation in intelligence. Strong directional selection tends to purge that variation. The best evidence indicate that most of that variation is due to effects from many genes (on the order of thousands), and I doubt that chimpanzee-human comparative genomics will yield much fruit here.

• Category: Science • Tags: Intelligence
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2 Comments to "Chimpanzees have quantitative traits, who knew?"

  1. Michael says:

    Although comparative genomics probably will not be able to sort this out in the near future, many feasible experiments could somewhat quickly get to the root of the difference between human and chimpanzee intelligence.

    I am not in any way condoning unethical experiments, but I just wonder if it would be possible to compile a list of technologically possible hypothetical experiments that could resolve this issue. Of course price is not an object in this hypothetical situation.

    For example, using existing modern technology, it should be theoretically possible to systematically substitute chimpanzee genome chunks of various sizes for the human versions. It would be easy to first define which regions are compatible with cellular viability, and then those allowing development into whole animals.

    Regions which are inviable could be screened in combination with all other regions to find regions which restore viability. In this way, the specific incompatible regions could be quickly narrowed down and these combinations would be eliminated from further experiments. The same thing could be done starting with humans, replacing genome regions with chimpanzee versions.

    All versions which are able to produce living animals would be systematically screened for intelligence, language ability, etc. Additional experiments could refine the resulting interesting genome regions.

    This could at the very least define whether the major difference between human and chimpanzee intelligence is actually defined by a very few or a large number of genetic regions.

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