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:

  • 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 mainland.

  • 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.

These differences are likely to systematically influence the form of species that form 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 inbreeding.

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 population.

- 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.


Tim Tyler | Contact |