大象传媒

Speciation

Alfred Russel Wallace created pioneering work in speciation; however, additional evidence over time has led to our current understanding of the theory of .

A is a group of organisms able to interbreed and produce fertile offspring.

New species can arise as a result of the following things:

  • genetic variation - each population has a wide range of that can control their characteristics
  • - the alleles which help an to survive are selected in each population
  • speciation - the populations become extremely varied and successful interbreeding cannot happen anymore

New species can also arise as a result of isolation:

  • two populations of a species can become geographically separated because of the environment
  • isolation can prevent interbreeding and the combination of genes within a species
  • different mutations can take place in the isolated groups and create different within a particular location
  • over time species may evolve to be different to each other, and they will not be able to interbreed

The diagram illustrates what could happen to an animal population, which is separated into two isolated groups by a geographical feature, such as a mountain or river.

A large population with a common gene pool, due to isolation they become two populations separated by a barrier.  Mutations appear in both populations.  Selection pressure occurs.  In one population a cold temperature means the hairy form has a selection advantage.  In the other population predation means the blue form has a selective advantage.  After a long period of time the two populations can no longer breed to produce fertile offspring so two new species have formed.

Charles Darwin described the speciation of finches after his studies of the birds on the Galap谩gos Islands, which are a group of islands roughly 1,000 km off the coast of Ecuador. Darwin noticed that the finches on the different islands were similar to each other.

Darwin's drawings of the different heads and beaks of finches
Image caption,
Darwin's drawings of the different heads and beaks of finches

However, Darwin's studies revealed that the finches had wide variations in their size, beaks and claws from island to island. The finches' beaks differed depending on the local food source. Darwin concluded that because the islands were distant from the mainland, the finches that had arrived there had changed over time.