Species Unity

Psychic unity of humankind

• The Psychological Unity of Humankind
• First Annual Colloquium on the Law of Transhuman Persons 32:00 (slides)
• Eliezer Yudkowsky - Strong AI and Recursive Self-Improvement 1.32:30 (slides)

Tooby and Cosmides (1990) make much the same argument more explicitly.

Yudkowsky's argument states:

In a sexually reproducing species, complex adaptations are necessarily universal.

Critique

From a strategic point of view we are especially interested in those species that have two kinds of males. It's almost like having a third sex. In fact the winged males look far more like females than they look like wingless males. Both females and winged males are almost believable as wasps, although they are tiny. But the wingless males are nothing like wasps to look at. Many have savage pincer jaws which make them look a bit like miniature earwigs going backwards. They seem to use these jaws only for fighting — lacerating and slicing to death other males that they encounter as they stalk the length and breadth of the dark, moist, silent garden that is their only world.

 - Climbing Mount Improbable, Richard Dawkins.

Since there are counter-examples, where did the reasoning go off the rails?

Obviously peacock tails are not universal - only half the peacock population exhibits them. Eliezer argues that males and females are the only exception to his proposed rule. There, he argues, one alelle cannot become dominant - since neither can exterminate the other.

However, it isn't just the case of males and females where different competing alleles can coexist. There's the whole phenomenon of frequency-dependent selection. Most people are familiar with this from blood types, and sickle-cell anaemia. Alleles with phenotypic effects involving disease resistance can be advantageous when rare, and disadvantageous when common - resulting in them never going near extinction or fixation.

The alleles for dark skin have not exterminated the alleles for light skin either - in that case they both exist, because they are advantageous in different physical locations.

Indeed species can vary so much from place to place that individuals become unable to breed with each other - the case of ring species.

Next, this premise is not very accurate:

If gene B depends on gene A to produce its effect, then gene A has to become nearly universal in the gene pool before there's a substantial selection pressure in favor of gene B.

Gene B can spread if gene A is present at a frequency of 20% in the population - provided it is not deleterious in the absence of gene A. Sure, then the selection pressure maintaining it is reduced by a factor of five, but that's not necessarily enough to kill it off.

Next, the idea that adaptations are literally universal ignores deleterious genetic mutations. Mutations can easily take out entire adaptations in a stroke - by affecting regulatory genes. At any time, the gene pool has many such deleterious mutations.

Next, even with a perfect working genotype, developmental processes can malfunction, resulting in adult phenotypic variation consisting of damaged phenotypes.

Lastly, even with a perfect working genotype, and no developmental problems, phenotypic variation does not necessarily depend on genetic variation. There's also the influence of the environment to consider. In general, the environment is quite capable of sending some organisms down different developmental paths depending on the circumstances in which they find themselves. This is known as phenotypic plasticity.

There are plenty of examples of phenotypic plasticity in humans - e.g. the effect is an important part of the reason why a Sumo wrestler and a racing jockey have different phenotypes.

Tooby and Cosmides

They argue that:

different adaptive personality strategies cannot, in principle, be coded for by different sets of genes that differ from person to person.

Would they be making this argument if Neanderthals were still around? What about Homo floresiensis?

Evolutionary psychology requires relative human uniformity to simplify its assumptions - and to make it as politically correct as possible. By minimising the significance of human differences it avoids being called racist. However, the extent of differences between groups of humans depends of historical factors concerning their degree of isolation from one another. This is not the sort of thing that can be argued about from an armchair.

In closing

It should also be observed that the alledged psychic unity of humankind can easily be over stated. The brain is fragile and malfunctions easily, and there are lots of different ways for it to go wrong. We have many individuals with malfunctioning brains in society - so there exists rather a lot of phenotypic variation in human minds.

Note: an early version of this essay was posted on http://www.overcomingbias.com/ - but was apparently identified by a robot as being possible blog spam - and never seems to have made it through to the list.

References

1. Richard Dawkins - Climbing Mount Improbable

2. John Tooby and Leda Cosmides, 1992. The Psychological Foundations of Culture. In The Adapted Mind, eds. Barkow, Cosmides, and Tooby.
3. John Tooby and Leda Cosmides, 1990. On the universality of human nature and the uniqueness of the individual: The role of genetics and adaptation..