Others held to the older view that there was something in virtue of which things were members of a species, but that this had nothing to do with their morphology, but with their relations of descent. Nothing else makes scientific sense. Typology is the view that there are 'types' - unchanging forms that are what makes a species what it is. Population thinking is a recent development in Western thought - it is the view that aggregates of individuals, groups, have a profile that shows a distribution of characteristics. Some organisms will be longer or shorter, heavier or lighter, and there will be a mean around which most individuals cluster.
Variation is a universal fact about all species.
Some parts are located in different environments, and natural selection, genetic drift and happenstance all work to make them different if they are isolated for long enough. Thus are new species created. The name of a species, according to Ghiselin and Hull, is a proper noun, the name of a single and unique individual that has a beginning, a history, and an extinction, and which also has a distribution in space. Homo sapiens is not, on this view, the name of a 'type' of rational animal as Aristotle had it, but the name of a particular lineage of hominoids that happened to develop language and ratiocination. If all humans were extinguished next year, they could never arise again.