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There are some behaviors that are clearly genetic and not learned, such as insect dance patterns.

How are such behaviors expressed in the organism?

Do the genes specifically code for some neural circuitry that is always the same when it is present in the genome?

So if the gene is absent, is that neural structure just absent?

My understanding is that genes code for proteins. So how can a group of genes lead to such complex behaviors by just being expressed as some proteins?

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    $\begingroup$ American biologist, researcher and Nobel-Prize recipient Gerald Maurice Edelman also asked similar question that how does a one-dimensional genetic code specify a three-dimensional animal? from the glossary of his book Topobiology. $\endgroup$
    – cinch
    Commented Nov 5, 2022 at 23:15

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I believe a full answer to your question would fill one or more books, but I thought for my answer, I would concentrate on one behaviour — genetic expression of aggression — and I think the jury is still out on the subject.

A quick Google search lead me to Psychology Hub where there is a write-up on genetic factors in aggression, including the MAOA gene, which is

a gene (monoamine oxidase A), that has been implicated in aggression, mice that possessed the gene were extremely aggressive. The MAOA gene is thought to affect neurotransmitters.

Many Google search results refer to the MAOA gene as the "warrior gene" such as McDermott, et al. (2009) or "criminal gene" such as Sohrabi (2015).

The Psychology Hub points out that the problem with implicating the MAOA gene is that the MAOA gene cannot account for all cases of aggression.

This is because MAOA-L is only present in about 1/3 of men in Western population, who therefore have higher levels of neurotransmitters because they haven’t been metabolised. MAOA-L is rarely expressed in women. This highlights that aggression [in] up to 2/3 of men and most women cannot be account[ed] for by the MAOA gene, this suggests therefore that there must be another explanation for aggression, making this explanation limited in its application.

I believe the fact that MAOA-L is only present in about 1/3 of men comes from Chen, et al. (2013).

Among the 152 men, 52 (34.2%) and 100 (65.8%) men have one MAOA-L allele and no MAOA-L allele, respectively.

On the subject of any genetic factor in aggression, a considerable amount of research into genetic factors in aggressive behaviour was conducted on animals, such as Lagerspetz’s (1979) research on mice. Psychology Hub elaborated on this.

Lagerspetz (1979) bred 25 generations of mice. In each generation she chose the most aggressive mice to breed together and the least aggressive ones to breed together. The result was two very different strains. One group of mice were super-aggressive, the other very docile. This research supports the role of genes in aggressive behaviour as it illustrates that when two mice holding the ‘aggressive gene’ reproduce, their offspring is significantly more likely to display high aggression (thus support a biological, genetic role in the presence of aggression).

The problem with this is that

the findings from this research cannot be extrapolated (generalised) to humans. Mice and humans are physiologically different and so, although there seems to be a genetic basis for aggression in mice, it doesn’t mean that such findings can be generalised to humans.

And, this research fails to generate any information regarding human aggression and links to genetics. However,

several studies have suggested that heritability accounts for about 50% of the variance in aggressive behaviour. Monozygotic (identical) twins share 100% of their genes, while dizygotic (non-identical) twins share only about 50%, as a result we would expect to find greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors.

Now, Psychology Hub points out that twin studies provide support for the genetic explanation of aggressive behaviour. One example they gave was

McGue et al (1992) found a correlation of +0.43 for MZ twins and +0.30 for DZ twins on aggression scales

This has been quoted in a few quizlet sites with no reference information and I cannot find the paper to support it. However, if true, as Psychology Hub points out

This suggests that genes play some part in aggressive tendencies as MZ twins share more genes than DZ twins, therefore if there was no genetic element to aggression we would not see any difference in the correlation for MZ and DZ twins.

References

Chen, H., Pine, D. S., Ernst, M., Gorodetsky, E., Kasen, S., Gordon, K., Goldman, D., & Cohen, P. (2013). The MAOA gene predicts happiness in women. Progress in neuro-psychopharmacology & biological psychiatry, 40, 122–125. https://doi.org/10.1016/j.pnpbp.2012.07.018

Lagerspetz, K. (1979). Modification of aggressiveness in mice. Aggression and behavior change, 66-82.

McDermott, R., Tingley, D., Cowden, J., Frazzetto, G., & Johnson, D. D. (2009). Monoamine oxidase A gene (MAOA) predicts behavioral aggression following provocation. Proceedings of the National Academy of Sciences, 106(7), 2118-2123. https://doi.org/10.1073/pnas.0808376106

Sohrabi S. (2015). The criminal gene: the link between MAOA and aggression (REVIEW). BMC Proceedings, 9(Suppl 1), A49. https://doi.org/10.1186/1753-6561-9-S1-A49

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This is a great question, which oddly seems to have received very little attention from academia. The simple fact is that genes code only for the polypeptide sequences used to build proteins. They contain no information about the specific patterns of synaptic connections in the brain underlying heritable mental capabilities, nor is there a mechanism by which genetic information could influence the making/breaking of such connections. Epigenetics (the influence of environment on gene expression) is therefore not going to help.

Evolutionary Developmental Biology goes some way to transcending the gene-centric viewpoint of living systems, but only addresses how the right cells get in the right place as the embryo develops. That is only a starting point for getting the right patterns of connections between them.

The closest I can find for an answer to this question is Developmental Systems Theory (see Susan Oyama's "The Ontogeny of Information"(2000) or Griffiths and Hochman "Developmental systems theory" eLS (2015)).

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