Parallel evolution is similar to convergent evolution
in that similar adaptations arise in different species.The
main difference is that in parallel evolution the two species have a relatively
recent common ancestor.
In convergent evolution the two ancestral lineages
have been separated for a much longer time.The
classic example of convergent evolution is the fishlike and fin-like shapes
in fish, some marine mammals, and some marine reptiles....because those
shapes are more efficient for a life in water.Another
example of convergent evolution in even more distantly related species
is the example of wings in butterflies and birds.
Because species are living in similar habitats and
have similar selective pressures on them, you tend to see similar adaptations.....such
as wings, or fins.
In parallel evolution you also have species with similar
adaptations because they live in similar environments, but in this case
they have a more recent common ancestor.Also,
the common ancestor does not have the feature(s) that the two descendant
species share.Apparently, the particular
trait(s) has (have) arisen more than once in descendants of the original
ancestor.
A classic example is how similar some of the marsupial
mammals in Australia are to placental mammals in South America. There
are many lines that resemble each other depending on the niche they have
filled on each continent.One example
is the
anteater-like features that have appeared in both
placental and marsupial lines.These
features have appeared separately in relatively closely related lineages
(both mammals). While this does not necessarily happen side-by-side
in space, as is the case with the concept of parapatric speciation, it
is comparatively "side-by-side" on the phylogenetic tree.
The real difference between convergent and parallel evolution depends on how one chooses to define the relative closeness of common ancestry.
Question 12 on the practice tells you that the two plants in question are not at all closely related.Obviously, they are in the same kingdom, but the example above (mammals) is of organisms that are in the same class.For the purposes of our class, any similar question I ask will be about convergence, rather than parallel similarities.