The models show the life cycles of a fish and a frog. explain why these life cycles show characteristics common to their class of vertebrates.

This is because all land vertebrates share a common ancestor. All land vertebrates emanated from evolution form the oceans and seas from a group categorized as Sacropterygii. Therefore during the early phylotypic stages of embryonic development, the embryos of all land vertebrates look alike morphologically. It is believed it is during this stage that the basic plan of the body takes shape before it begins to diverge.

•there must be variation for the particular trait within a population.

•the variation must be inheritable (that is, it must be capable of being passed on from the parents to their offspring).

•individuals with one version of the trait must produce more offspring than those with a different version of the trait.good

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