Answer:
All mammals, like dogs, cats, and humans; reptiles, amphibians, fish, birds, and even insects.
Explanation:
All mammals, like dogs, cats, and humans; reptiles, amphibians, fish, birds, and even insects are the animals that have a complete tube-like gut with two openings. A system having a tube with two openings i.e. mouth and an anus is called tubular system. In this tubular system, the animals eat with one opening and the other opening is used for excretion of waste and nitrogenous materials from the body so that's why most of the animals have two openings.
One of the major elements of natural selection is that all species have genetic variation. Natural selection is a process when organisms adapt better to their environment. It is an essential key in evolution. There is a change in phenotype of a population over time.
