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:
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