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