[Post 2] How does one species become another?

How does one species become another?

Within a species, each individual slightly varies in its genes, environment, behaviour and cognitive ability – the same as humans. Each slight variation can either benefit, have a neutral effect or cause a cost to the individual. The variation amongst individuals means that some survive better or reproduce better than others. The individuals who have the most beneficial variation usually are fitter and produce more offspring. The genes are then passed onto the individuals young. These offspring are fitter, so produce fitter offspring when they reach adulthood. Meanwhile, poorly adapted individuals, who have these costly variations/traits, suffer morbidity or mortality resulting in their genes not being passed on to future generations. Therefore, traits that increase fitness are ‘favoured’ by natural selection. This is where the well-known phrase “the survival of the fittest” originates.

Speciation is the name of the evolutionary process of forming a new, discrete species. There are two forms of speciation; sympatric and allopatric.

Allopatric speciation occurs when a new species arises as the result of a physical barrier from its original species (usually a geographical feature, such as a river or a mountain range). The barrier stops the flow of genes from one population to another, and coupled with environmental factors (that lead to different selection pressures), the species diverge from one another. This form of speciation has occurred in some species of monkeys within Africa, partly due to the Congo and Sanaga rivers.

Sympatric speciation is when a new, distinct species arises without being spatially isolated from its original species but due to a non-physical barrier. For example, producing infertile young or differences in courtship behaviours. These barriers prevent successful mating/reproduction. Differences in mating behaviour have stopped the interbreeding of two chiffchaff species, the common and Iberian, in Spain and France.

The image below illustrates these forms of speciation: