The Evolution

Evolution started millions of years ago and is still happening today.

Isolating mechanisms lead to speciation, that is, the process by which one or more species arise from a previously existing one. The isolation mechanism interrupts gene flow within the population hence imposing genetic isolation. If such genetic isolation persists for a long enough time speciation occurs. There are two different types of speciation depending on whether the members of the population involved are found in the same or different geographical area:

·         Allopatric speciation: 79925322

This occurs while the populations are geographically separated by mountain ranges, seas, rivers or habitat preferences. When the species adapts itself to the new conditions natural selection starts acting on those traits that make the organism better adapted to the environment thus leading to change in allele and genotype frequencies.

·         Sympatric speciation:

This occurs due to some form of reproductive isolation mechanism within the same geographical area. Such reproductive isolating mechanism may be structural, physiological, behavioural or genetic. The prolonged interruption of gene flow leads to speciation. For example, in the case of two particular species of finches co-existing on the Galapagos archipelago, the reproductive isolating mechanism is physiological because the difference in the beak size makes them unattracted to each other in the breeding season. Such change in beak size could be accounted to the fact that the two finch species feed on different types of food.

Isolating mechanism can be either pre-zygotic or post-zygotic.

Pre-zygotic reproductive barriers prevent individuals of different species or populations from interbreeding and therefore there can be no formation of offspring. There are various types of pre-zygotic reproductive barriers:

·         Habitat isolation. Individuals of different species may select to live in different habitats or acquire different niches in the same general area such that they never come into contact during their respective mating periods.

·         Temporal isolation. Many organisms have very short mating periods that last a few days or hours. If the mating periods of the two species do not overlap they will be reproductively isolated by time.