How New Species Form: Isolation and Speciation

0:00How does one species split into two new species?

0:04In biology, a species is usually defined as a group whose members can interbreed and have fertile offspring, young that can breed too.

0:14This is one population of beetles: members of one species living in one area and breeding together.

0:22A barrier can split a population: a river, a mountain range or a rising sea.

0:29Here, a river splits the population into two halves.

0:34The halves cannot meet, so they stop interbreeding. This is called geographic isolation.

0:41Over many generations, each half changes separately.

0:45Each side gets its own mutations, random changes in DNA, and natural selection favours different traits on each side.

0:54Much later, the river dries up and the groups meet again.

0:58But they can no longer interbreed and have fertile offspring. This is called reproductive isolation.

1:05They are now two separate species.

1:09Forming new species is called speciation. When a barrier causes it, it is allopatric speciation, meaning other homeland.

1:19Without a barrier, in one place, it is called sympatric speciation, meaning same homeland.

1:26In plants, a mistake in cell division can double the chromosomes, for example from 6 to 12.

1:34The new plant usually cannot have fertile offspring with the parent plants, so it can be a new species in one generation.

1:42New species form when groups of one species can no longer interbreed.