Spadefoot Toads can develop into 2 different morphs, one is carnivorous, and the other omnivorous. In ordered to develop into the carnivorous morph, the jaw develops at a faster growth rate than the rest of the body; this is an example of:

Allometry

Explanation:

Allometry explains how the body parts grow at different rates such that the jaw of the spadefoot toads develop it's jaw at a rapid rate than other body parts.

Thus, the differential growth rate shown in the carnivorous morph is to aid feeding and hence survival.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".