|
Euphorbia obesa
(family Euphorbiaceae)
Astrophytum asterias (family
Cactaceae)
|
The evolutionary
convergence is the recurrent tendency of
living beings
to arrive at the same 'solution' to a particular 'biological
problem” that can often only be handled in one of a few ways, some
particular patterns emerge over and over again in very different
organism.
Structures that are the result of
convergent evolution are called
analogous structures or
homoplasies; they should be contrasted with
homologous structures
which have a common origin.
An example of convergent evolution is the similar external
appearance of the ribbed stems of some
cacti,
euphorbias, Stapeliads and of
other succulents belonging to different family. All them serve the same
function and are similar in structure, but each evolved independently.
An other example:
The Mexican
Astrophytum asterias (family
Cactaceae) resembles enough to the South African
Euphorbia obesa
(family Euphorbiaceae), but only in the field of the external
anatomy,
this being due to the environmental
condition in which these two types of plants live.
Parallel evolution occurs when two independent
species evolve together at the same
time in the same ecosystem and
acquire similar characteristics |
