photo by Franz Lanting
A third mechanism by which species may evolve is known as
This allows a species to take on traits which were
prevelant in an earlier stage of development, often embryonic. This is well demonstrated by
the resemblence (minus the fat!) of humans and chimpanzee infants.
Another important concept to be kept in mind is that if a species acquired a new morphological character (or characters) during an early phase of evolution, as the environment continually changes over time and the species either becomes extinct or adapts, it may lose or accentuate that earlier derived trait.