Over the last 100 years or so, there has been a large volume of research into the human 'disgust' response.

See Wikipedia

Although there are (slight) cultural differences across the world's populations, it's currently regarded as a truly 'innate' (rather than learned) emotionplugin-autotooltip__plain plugin-autotooltip_bigEmotions

Theories about emotions stretch back at least as far as the Stoics of ancient Greece, but to date, no definitive taxonomy of emotions exists - though several have been proposed. And many of the explanations about the apparent biological necessity for some of the emotions (e.g. 'boredom' or 'shyness or 'embarrassment') remain sketchy and controversial. response - one which has fairly obvious evolutionary advantages. As an example, a 'disgust' response to rotting food may well save lives, and so people with this facility have the opportunity to pass on the trait to future generations.

There is currently no explanation as to how such behaviours can be biologically 'passed on'. As far as in known, the only routes would be through genetics or epigenetics (outside the genes), and there's no accepted theory about how they could code for complex behaviours.

Note: This is just one example of the numerous - and sometimes complex - behaviour patterns which are somehow inherited, by as-yet-unknown mechanisms. See Instinct and Inheritanceplugin-autotooltip__plain plugin-autotooltip_bigInstinct and Inheritance

inexplicable

Complex behaviour patterns can be learned, but they can also be inherited.

Example 1 The female Common Cuckoo (Cuculus canorus) is a so-called 'brood parasite' - in that it lays its eggs in the nests of other birds. This can't be a 'learned' behaviour, since the bird has never met its parents (except in un-laid egg form) The cuckoo somehow inherits this behaviour - presumably via some as-yet-undiscovered genetic mechanism.