Natural
selection
Natural selection is exerted on living things on which their survival depend on the natural environment.
Generally speaking in the animal world, the individuals which are resistant and can fight in a hostile environment are at the origine of the evolution of its own species.
Natural
selection is the process by which favorable traits that are heritable become
more common in successive generations of a population of reproducing organisms,
and unfavorable traits that are heritable become less common.
When
organisms are of the same species, all the organisms in that group must have
commun features but the individuals in the group do not need to be identical.
Some features may be different.
The animal world shows many examples of these aptitudes of variation brought about by ecological selection and sexual selection
The
ecological selection
Animals have to feed and shelter themselves until they can reproduce themselves
to ensure the survival of their species. The environmental changes have made
animals have to adapt and perfect their abilities in order to ensure their survival.
Often, natural selection acts on specific traits of an individual :
"Biston
betularia" is a moth which lives on the barks of birches.
In
the English industrialized environment during the XIXe century, this species
evolved by adaptating the colour of its wings from lighter to darker due to
the polluted industrialized environment. Populations of strongly black spotted
butterflies could escape the sight of predatory birds by posing on the black
bark of birch trees. Thus,
these butterflies could survive and multiply. Taking into account the surrounding
factors, these individuals would undoubtedly have acquired other aptitudes for
survival. However, the ones that were born with very white wings had less of
a chance of surviving and therefore reproducing. By adapting their wing colours
to the industrial conditions the species would have definitively transferred
and adapted..
** This example of the butterfly "Biston betularia" was largely used in scientific handbooks to illustrate one of the principles of natural selection. Now, however, this example of the way in which the investigation about the change of the butterfly was carried out is being disputed. The principle of the selection being favourable for the evolution of the species remains valid. In this case study, the evolution of the butterfly results in two phenomena : A modification of the environment and a mutation of variations that give an advandtage to individual bearers that will survive easier than others.
For Biston betularia, the dominating factor of evolution is its colour in a changing environment. For other animal species like Darwin's finches, the factor of change is food and the necessity of adapting in a new environment.
For Darwin and his contemporaries, natural selection was thus essentially synonymous with evolution by natural selection. Nowadays Natural selection remains the single primary explanation for adaptative evolution but it is perceived by some scientists to be too weak to explain the range of observed characteristics. The union of traditional darwinian evolution with subsequent discoveries in classical and molecular genetics is termed in the modern evolutionary synthesis.
The sexual selection
It
is the case for animal sexual rituals and variations of individual distinctive
traits that are remarkable.
The sexual rituals are strictly coded within species that are closely related.
When the code is badly reproduced by an individual, it prevents the mating of
two individuals belonging to different species or the mating of the one which
is an uncapable.
Among much animal behaviour, there is a unit of behaviour which is conveyed within the same species without any individual learning. At this stage, the ideas which are builders of organics are raw memory. These values are essential to inform the species of the right behaviour to have its own life.
Animal natural selection is also based on values of sensory reflexions which are highly developped for one or two of their senses. Much of animal performances are higher than that of man.
The collective consciousness records the series of animal behaviour conveyed by the species, the incorrect reproduction of which brings about the process of individual elimination.
Man is subjected to this evolution process like any other animal species but the selection is a