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Can the behavior/psychology of a human be genetic or is it an acquired trait?

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closed as too broad by terdon, jarlemag, biogirl, Chris, leonardo Apr 16 at 20:38

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You will need to be way more specific than that. What behavior? Which aspect of psychology? –  terdon Apr 16 at 12:20

1 Answer 1

What do you call an acquired trait? A trait acquired during the lifetime of the individual through its relationship with the environment (especially culture and traditions in humans)?

If you take any population of living organisms, the variance of quantitative trait in this population, also called phenotypic variance and denoted $V_P$ is the result of the sum of the genetic variance $V_G$ and the environmental variance $V_E$ (and two times the covariance between genes and environment $V_{GE}$ but we'll neglect this factor for ease in this post). One has to understand the meaning of environment. The environment is anything that is extern to the individuals. It includes temperature, food, predators, other individuals of the same species, culture, ….

In other words (again it is slightly simplified):

$$V_P = V_G + V_E$$

The division of the genetic variance by the phenotypic variance gives you the so-called heritability (in the braod sense, because there are the heritabilities in the broad and in the narrow sense). Psychology or behavior are traits like any others that follow this same rule. This concept does not make sense for one single individual. You cannot say that for one individual 40% of its behavior is genetic and 60% is environmental. It makes only for a population to say that 40% of the variance in this behavior is due to genetic variance and 60% is due to environmental variance. Note: The higher is the relative importance of the genetic variance, the higher is the response of this population to selection.

For example height in human has a heritability of 60% to 80% (depending on the estimates), which mean that 60% to 80% of the variance is due to genetic variance. Language that we speak is typically a trait that has zero heritability. If you raise a brazilian baby in Japan, (s)he will speak japanese without any accent. Therefore, all the variance in language is only explained by the environmental variance.

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Thanks for the response! Firstly, I clarify what I meant by the 'acquired trait' here. I didn't mean it in terms of the technical jargon (i.e. the biological terminology). By 'trait' I meant literally any quality (mostly behavioral and not importantly physical) of observed human nature e.g. moral values, greed, hatred etc. My motivation to ask this question came form this answer: qr.ae/vHUfU which says that some part of the motherly nature come from genetic reasons and has to do with evolution. What if I talk about the tendency of greediness in humans? –  Devashish Singh Apr 16 at 11:00
Does greediness has anything to do with evolution or genetics? Or as you mentioned it can be acquired (only?) through the environmental factors? Or such qualities also have zero heritability? –  Devashish Singh Apr 16 at 11:08
What part of the total variance in greediness has to be accounted to genetic variance? or, as you said "what is the heritability of greediness". It is quite hard to accurately define and measure a personality trait. But some people did their best. I think about David Cesarini (an economist, not a biologist) for example, but I'm sure there are many other people that measured the heritability of personality traits. –  Remi.b Apr 16 at 11:36
I made a quick search and couldn't find any information about "greediness". Generally speaking, personality traits have a heritability around 0.4 I think but one should really check further that taking my words for granted. You should have a look to this review. It seems accessible to non-biologist –  Remi.b Apr 16 at 11:37
In reaction, to your question I posted this question. You will probably be interested to see what answers come out (if any). –  Remi.b Apr 16 at 11:48

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