The Character of New Species
New species differ from their ancestors
When speciation happens, it is not common for a population to split into two
identical halves, which share the same circumstances.
More common is for there to be an asymmetry between the two populations.
This asymmetry is likely to take one of several characteristic forms - and
there are characteristic forms associated with new species.
Speciation on islands
One of the more common forms of geographic isolation involves a population
confined on an island.
Here a small population is divided from the ancestral one by a physical barrier
- in the form of an expanse of water. While the populations are separated
genetic drift - and perhaps differing selection pressures - results in the
division between the species being permanent.
The island habitat is likely to be different from the normal one:
These differences are likely to systematically influence the form of
species that form on islands.
- Islands are more closely associated with water - since they are surrounded
by it on all sides.
- Islands are more likely to be flooded than other areas - since they are
surrounded by a region at sea level.
- Islands are likely to have a different ecosystem. Due to their small size -
they are less likely to be inhabited by predators - and more likely to be
relatively uninhabited. If there are vacant roles in the resulting ecology,
they are more likely to be adopted by birds.
- Islands are likely to experience different weather from most areas of the
- Islands are more likely to be under the influence of vulcanism. A quick
glance at a [volcano map]
shows that many of the worlds volcanos are on islands.
Small population size
Another set of circumstances that are likely to arise for a new species is
small population size.
This could happen through isolation on an island - or simply
through not getting off the ground very quickly.
Small population size can increases the difficulty in finding mates, problems in
defending groups, problems with the division of labour - and can lead to
A gene pool of reduced size will mean that many alleles get lost - changing the
typical context in which the remaining genes find themselves expressed.
Sandy Hodges expressed the idea clearly:
An isolated population first becomes inbred,
and then changes through genetic drift, with almost all changes for the
worse. The result is an organism strikingly less fit. But in some
cases, the isolated population will have no competitors: for example, if
the population is on an island. Even though the population becomes
less fit, it does not go extinct. In this genetically weak state,
almost any direction is up, so a mutation has a chance to get
established, which would never get a chance in the mainland
- Sandy Hodges
If the population size remains small for extended periods, adaptations to deal
with the new circumstances - may result. For example, difficulties in finding
mates may result in finer sensory acuity, which is better able to locate them.
When a new species becomes reunited with its parent population any
asymmetries between them are likely to be magnified:
The new species is likely to face problems in making sure it mates with
members of the right species.
Mating with members of the parent species may be a waste of time - or much
worse, it may result in pregnancy - resulting in what are likely to be sterile
or malformed hybrids.
As a result of this there is pressure on the new species to diverge rapidly
from it's parent population - and to become better able to recognise members of
its own species.
The process is known as "reinforcing selection". It acts to more-completely
separate a partially-separated population.
It is likely to act on those characteristics which differ naturally between the
species involved. The effect is to greatly magnify those differences.
The differences sometimes turn into distinctive species markings or scents -
and an improved ability to recognise one's companions using these signs.
The long term fate of two species occupying very similar niches seems most
likely to be extinction for one party. Divergence into differing niches which
are able to co-exist will be a possible - but probably unlikely result.
Competition between two similar species represents a rather different sort of
race from competition with other individuals within your own species.
If there are multiple species there is more scope for the two trying
divergent strategies. A singe species is less able to do this - since
it would typically involve some sort of polymorphic morphology.
Competition between the species may consequently result in a different set of
selection pressures being applied - as compared to those that would normally
arise if only one species was present.
New species often differ from their parent species in a number of ways. These
are likely to include an increased probability of sharing an island habitat, and
a smaller gene pool.
The resulting differences may be magnified by reinforcing selection.
The presence of another competing species in itself will constitute a
significant change to the environment of a species.
It seems likely that speciation results in quite a range of changes to the
"fitness landscape" of a population. We hypothesize that these changes may act
to knock that population out of "local minima" - possibly resulting in a better
adaptive fit overall.