Travel Reference
In-Depth Information
to defi ne their ecological niches. If there were only one species of bamboo
in the forest, producing the same amount of cyanide in each of its tissues,
instead of a mix of species and subspecies that have dif erent amounts of
cyanide in dif erent tissues, there might not have been ecological room for
three species of bamboo lemur.
The appearance of new species
How did these dif erent lemur species fi rst arise?
The process of speciation starts whenever a group of animals or plants
is selected to live in a particular ecological niche, but this is only part of
the story. Unless this group is isolated from other groups so that it cannot
exchange genes freely with them, it will not become a species.
Let us suppose that a group of lemurs colonizes some new patch of forest,
such that this group is completely separated physically from other lemurs.
Then, over time, it will become better-adapted to its new ecological niche.
There are two reasons for this. First, the genetic variation already contained
in this group will be shul ed to produce new combinations of genes each
generation. Some of the combinations will confer high fi tness under these
new environmental conditions, and the more favorable of the genetic vari-
ants will increase in frequency. Second, as a result of mutations, the gene
pool of this group will begin to accumulate more and more genetic dif er-
ences from other lemur groups. A few of these mutations will be favorable
and increase in frequency because of selection, while other mutations that
have less selective ef ect will replace older alleles in the population simply
by chance. The result is that the group's gene pool will become more and
more dif erent from the gene pools of other closely related lemurs.
Eventually the isolated group of lemurs will become so genetically dif erent
from other lemur groups that if the physical barriers that separate them should
disappear, allowing them to mix, hybrids with the other groups will be sterile
or unable to survive. This is because combinations of genes that work well
within the respective populations will come together for the fi rst time in the
hybrids. Some of these new gene combinations will adversely af ect hybrid
