In evolutionary biology, parallel evolution
refers to the independent evolution of similar traits in closely
related lineages of species, while convergent evolution refers to the
appearance of striking similarities among lineages of organisms only
very distantly related.
One of the most
spectacular examples of parallel evolution is provided by the two main
branches of the mammals, the placentals and marsupials, which have
followed independent evolutionary pathways, after splitting off from
some primitive mammalian common ancestor in the late Cretaceous.
(Placentals bear their young fully developed, while marsupials give
birth prematurely and nurture their young in a pouch.) The marsupials
of Australia have evolved in isolation from placental mammals elsewhere
yet have given rise to a whole range of similar forms: pouched versions
of anteaters, moles, flying squirrels, cats, wolves, etc. Much the same
phenomenon occurred in South America, where marsupials independently
gave rise to a range of parallel forms.
Parallel evolution can be distinguished from convergent evolution and evolutionary relay. In convergent evolution, unrelated lineages acquire similar characteristics (bird and bat wings).
Similar to convergent evolution, evolutionary relay
describes how independent species acquire similar characteristics
through their evolution in similar ecosystems, but not at the same time
(dorsal fins of sharks and ichthyosaurs).
Examples
- In
the plant kingdom, the most familiar examples of parallel evolution are
the forms of leaves, where very similar patterns have appeared again
and again in separate genera and families.
- In butterflies, many close similarities are found in the patterns of wing colouration, both within and between families.
- Old
and New world porcupines shared a common ancestor, both evolved
strikingly similar quill structures; this is also an example of
Convergent evolution as similar structures evolved in both Hedgehogs
and Echidnas.
- Contemporaneous evolution of the
extinct browsing-horses and extinct paleotheres both of which shared
the same environmental space.
|
