Everything from available food to climate will cause the changes we see in natural selection. Random mutations occur constantly and when those mutations are beneficial for life, the genetic code is more likely to be passed on to future generations.
natural selection effects of environmental pressure
Natural selection (the driving force of evolution) is the selection of genetic variations by how they effect the organism's chances of survival or reproduction. If they diminish it's chances, the organism or it's immediate offspring die and the gene is gone. If the genetic variations increase it's chances, then it survives. Without genetic variations there can be no evolution. Natural selection is the selection (by environmental pressures) of those variations.
Adaptation does not allow for natural selection: natural selection causes adaptation.
Genetic variation in itself does not 'support' natural selection: it is what natural selection acts upon.
They are the selective agent in natural selection ;)
Natural selection is only the result of changing environments, mutation and the variation resulting therein. Natural selection is the process of adaptive change and the main mechanism of evolution that leads to speciation. Natural selection is a process as mutation and variation are grist to the mill of natural selection.
Selection pressures
Spontaneous genetic mutation and pressures exerted on the species by the environment.
Natural selection is the process of selection imposed by pressures from the environment. It has no conscious guidance or purpose, but simply selects for a population best suited to survive in the current environment.Artificial selection is the process of selection consciously imposed by humans selecting which individuals breed. This can be considered a subset of natural selection, if one considers humans as just another part of the environment other creatures must live in.
These plants and animals were subjected to artificial selection so that the traits humans wanted in the organisms were selected for and the organisms not having these traits were culled. This, with some modification, is a good analogue for natural selection and artificial selection shows how organisms can be shaped over time with the proper selective pressures. The selective pressure of humans in artificial selection and the selective pressure of the environment in natural selection.
Natural selection varies the death rates of individuals in the current generation. As the next generation is born with different traits derived from parents that were survivors of the current generation, the population changes gradually from generation to generation better able to survive longer against the natural selection pressures. Should selection pressures change in the future (and they very likely will) the direction of changes caused by natural selection will also change (with a corresponding but temporary increase in death rates if the change is large and sudden).
Its NaTuRaL sElEcTiOn if you didn't know.
Mathematical analysis in genetics and comparative genomics can show scientists to what degree a particular genetic sequence resulted from selection pressures at a given time in the evolutionary history of the organism under consideration.
natural selection
Natural selection (the driving force of evolution) is the selection of genetic variations by how they effect the organism's chances of survival or reproduction. If they diminish it's chances, the organism or it's immediate offspring die and the gene is gone. If the genetic variations increase it's chances, then it survives. Without genetic variations there can be no evolution. Natural selection is the selection (by environmental pressures) of those variations.
Adaptation does not allow for natural selection: natural selection causes adaptation.
Genetic variation in itself does not 'support' natural selection: it is what natural selection acts upon.
Natural selection is what causes adaptation.