On Theories of Organic Evolution and their Relevance to Modern Genetic-Systems Theory

Biologists of the 19th Century centered their work around the evolution of structural organization. Their general method was to collect one or more specimens of new or unfamiliar plants and animals, kill and preserve them, describe them carefully both internally and externally and on the basis of this evidence, compare them with known species and group like with like. If the new specimens were unlike any known before, they assumed that they had found a new species. They next assumed that the more similar two species were in form and structure, the more closely related they were, and they tried to deduce how one could have changed into the other, and in what order.