Question

In the real world, are populations likely to be in Hardy-Weinberg equilibrium?

Answer 1

The short answer is no.

Consider some of the main assumptions of Hardy-Weinberg equilibrium:

1. Mating is random
2. Population is large
3. No mutations
4. No migrations
5. No natural selection

In the real world, these assumptions (with the exception perhaps of #5) are not applicable. Mating is far from random (otherwise people wouldn't spend so much time dating each other). Populations may be small (e.g. a village of 100 people). Mutations are unavoidable (although they often do not affect an individual's reproductive success). People move around all the time (e.g. immigration). You could argue that humans are less susceptible to natural selection (e.g. due to modern medicine), although third-world or pre-industrial populations likely still experience natural selection to some degree.

If we're talking about animals, none of these assumptions are true for similar reasons (although migration may be less important for some species and natural selection will play a way bigger role).