list three factors responsible for speciation.Describe each one of them?
Speciation is the process in which one or more species arise from previously existing species. A single species may give rise to a new species or two different species may give rise to a new species.
There are many factors responsible for speciation.
Geographical barrier
Natural selection
Genetic drift
Geographical barriers
Speciation can occur due to formation of extrinsic geographical barriers (such as rivers, mountains, etc) between two populations which allows no gene flow. Genetic differences gradually accumulate (due to natural selection and genetic drift) between these two populations and result in evolution of reproductive barrier between two populations such that they are called two species.
Speciation can also occur in incomplete geographical isolation which allow reduced gene flow between populations. The incomplete geographical isolation of populations is not sufficient to cause speciation, so in such conditions also other selective pressures are required to alter the gene frequency so much that that they cannot mate and become two species.
Natural selection
Darwin and wallace proposed that natural selection is the mechanism by which new species arise from pre existing ones. Natural selection states that there is "struggle for existence" within a population and variation exists within all population. The continuous competition between individuals for environmental resources creates a 'struggle for existence' and this struggle makes sure that certain organisms would fail to survive or reproduce. This would eliminate less suited organisms and better adapted organisms would survive and pass on their traits to next generation leading to evolution.
Or in other simple words, If the environmental condition changes than the population which has adaptation in the form of mutation to adapt to changed environmental condition will be selected by nature and survive. This is called natural selection.
Genetic drift
Genetic drift refers to the fact that variations in gene frequencies within populations can occur by chance rather than by natural selection. Random genetic drift may be an important mechanism in evolutionary change in small or isolated populations. In a small population not all the alleles which are representative of that species may be present. Chance events such as the premature accidental death prior to mating of an organism which is the sole possessor of a particular allele from the population. For example, if an allele has a frequency of 1% in a population of 1 000 000 then 10 000 individuals will possess that allele. In a population of 100 only one individual would possess that allele so the probability of loosing that allele by chance is much greater. Just as it is possible for an allele to disappear from a population, it is equally possible for it to drift to a higher frequency simply by chance. Random genetic drift, as its name implies is unpredictable. In a small population it can lead to the extinction of the population or result in the population becoming even better adapted to the environment or more widely divergent from the parental. In due course, this may lead to the origin of a new species by natural selection. Genetic drift is thought to have been a significant factor in the origin of new species on islands and in other reproductively isolated populations.
There are many factors responsible for speciation.
Geographical barrier
Natural selection
Genetic drift
Geographical barriers
Speciation can occur due to formation of extrinsic geographical barriers (such as rivers, mountains, etc) between two populations which allows no gene flow. Genetic differences gradually accumulate (due to natural selection and genetic drift) between these two populations and result in evolution of reproductive barrier between two populations such that they are called two species.
Speciation can also occur in incomplete geographical isolation which allow reduced gene flow between populations. The incomplete geographical isolation of populations is not sufficient to cause speciation, so in such conditions also other selective pressures are required to alter the gene frequency so much that that they cannot mate and become two species.
Natural selection
Darwin and wallace proposed that natural selection is the mechanism by which new species arise from pre existing ones. Natural selection states that there is "struggle for existence" within a population and variation exists within all population. The continuous competition between individuals for environmental resources creates a 'struggle for existence' and this struggle makes sure that certain organisms would fail to survive or reproduce. This would eliminate less suited organisms and better adapted organisms would survive and pass on their traits to next generation leading to evolution.
Or in other simple words, If the environmental condition changes than the population which has adaptation in the form of mutation to adapt to changed environmental condition will be selected by nature and survive. This is called natural selection.
Genetic drift
Genetic drift refers to the fact that variations in gene frequencies within populations can occur by chance rather than by natural selection. Random genetic drift may be an important mechanism in evolutionary change in small or isolated populations. In a small population not all the alleles which are representative of that species may be present. Chance events such as the premature accidental death prior to mating of an organism which is the sole possessor of a particular allele from the population. For example, if an allele has a frequency of 1% in a population of 1 000 000 then 10 000 individuals will possess that allele. In a population of 100 only one individual would possess that allele so the probability of loosing that allele by chance is much greater. Just as it is possible for an allele to disappear from a population, it is equally possible for it to drift to a higher frequency simply by chance. Random genetic drift, as its name implies is unpredictable. In a small population it can lead to the extinction of the population or result in the population becoming even better adapted to the environment or more widely divergent from the parental. In due course, this may lead to the origin of a new species by natural selection. Genetic drift is thought to have been a significant factor in the origin of new species on islands and in other reproductively isolated populations.