United States or Bhutan ? Vote for the TOP Country of the Week !
Both natural and artificial selection are partly specific, and partly intra-specific or individual. Nature of course, and intelligent men first chose the best elementary species from among the swarms. In cultivation this is the process of variety-testing. In nature it is the survival of the fittest species, or, as Morgan designates it, the survival of species in the struggle for existence.
Intra-specific selection is thus seen to fall under two heads: a selection between the individuals, and a choice within each of them. The first affords a wider and the latter a narrower field. Individual variability, considered as the result of outward influences operative during extreme youth, can be excluded in a very simple manner.
In detail, the struggle for existence is intra-specific, involving some form of competition or rivalry among the members of a single species; it is inter-specific, as a conflict is waged by every species with other kinds of living things; and finally it involves an adjustment of life to inorganic environmental influences.
For the sake of clearness we might designate the last named process with the term of intra-specific selection, and it is obvious that this term is applicable both to natural and to artificial selection. Having previously dealt with species-selection at sufficient length, we may now confine ourselves to the consideration of the intra-specific selection process.
Some flowers and garden-plants afford further instances. By far the greatest majority of improved asexual varieties, however, are not the result of pure intra-specific selection. They are due largely to the choice of the best existing elementary species, and to some extent to crosses between them, or between distinct systematic species.
Word Of The Day