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I'm talking about things like the tendency to feel sleepy after eating, avoidance of excrements, general preference for sweet foods, etc. Do all those characteristics have biological or evolutionary basis?

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closed as too broad by mgkrebbs, David, Bryan Krause, De Novo, Satwik Pasani Jan 28 at 12:48

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Your question is super broad. The "evolutionary explanation" for single traits itself is quite difficult and you are asking about many complex traits. $\endgroup$ – WYSIWYG Jan 25 at 10:27
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What is heritability?

First of, please read about the concept of heritability. See for example the post Why is a heritability coefficient not an index of how “genetic” something is? You should be able to understand why all else being equal, why if environmental variance for a given phenotype increase it results in a decrease in heritability and why directional selection in a population decreases heritability.

Do you now know what heritability is and is not?... Good!

Your question is very broad...

As you now understand, heritability is a concept define for a given population in a given environment and most importantly for a given trait. There is no way to give a single answer for all traits one might want to consider.

By experience, it seems that, in humans, most behavioural traits that we decided to investigate has heritability estimates in the order of 0.05 - 0.6.

One example

I will consider just one of the trait you list, "preference for sweet foods". Sweet taste preferences appears to have a high heritability in humans with estimates of the order of 0.41-0.66 (Keskitalo et al., 2007). For heritablities about other food preferences, you might want to have a look at Reed et al. (1997; there are probably more recent papers that make better reviews though).

Preference for sweet foods

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  • $\begingroup$ What I think is not immediately clear in this answer in response to a question like the OP is that heritability in the contexts you are presenting refers to variation in the population. If you look at the heritability of, say, height, that coefficient completely misses that evolution led to human-sized humans and not ant-sized humans, which is definitely genetically encoded. $\endgroup$ – Bryan Krause Jan 25 at 19:42
  • $\begingroup$ @BryanKrause Yes, this is why I insisted that the OP looks for what heritability means and I highlighted that directional selection actually reduces heritability. But I agree with you, when rereading the question, that the question should probably be be closed as it is not asking so much about heritability but more whether "it is explained by evolution", which does not mean anything. $\endgroup$ – Remi.b Jan 25 at 21:15
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    $\begingroup$ I actually voted to close. Then removed my close vote when starting to write a comment that was too long, so I made an answer. Maybe, I should have just kept with my close vote. Anyway, I can't vote to close anymore! $\endgroup$ – Remi.b Jan 25 at 21:16
  • $\begingroup$ Yeah, I know that and you know that but I don't think your answer here or the linked one conveys that message in easily, quickly digestible format. I do think the right thing in the end will be to close this question. $\endgroup$ – Bryan Krause Jan 25 at 21:58

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