What is Speciation? | A Level Biology Revision

Speciation is pretty much the evolution of new species from existing species. A species being a group of organisms with similar genes which are able to interbreed to produce fertile offspring. If populations become seperated (geographical isolation) then they are no longer able to interbreed. This might be for a number of reasons  - lets take a huge mountain for example. Selection pressures will be different in both locations, for example ease of getting food or temperature may differ. Within these slightly different environments some are better able to compete than others - this  causes the allele frequencies to change in each population. The genes then, over time become so different they now can't interbreed.

Other keywords:

Stabilizing selection - this is selection which tends to favor the average (gets rid of the extremes)
Directional selection - this favors one extreme

This is specifically for AQA A Level Biology Unit 4

How are new species formed?

Speciation is pretty much evolution in action, two species emerge from a single one. Because they share gene pools they have similar genes.


This pretty much works from the fact that new species can only form from pre-existing species. The idea is that a group of organisms from the space species can become separated geographically so they can't reproduce, this is called geographical isolation. When the two groups are completely separated, the two areas can have different environments. Like in every habitat there are some individuals which are better adapted to compete. These are more likely to survive and reproduce, this means the alleles (genes they have) are more likely to be passed onto their offspring. This means that over many generations the allele frequency increases so the individuals are better adapted to live in that environment. Eventually, the alleles present in one group 'evolve' and can become completely different to how they were initially. Because they might be completely different they won't be able to interbreed to produce fertile offspring, so they're now no longer the same species. 


Definitions


Species: A group of organisms which can interbreed to produce fertile offspring, they also share a gene pool.