A number of biologists after Darwin thought that geography and isolation underlay speciation, and indeed the entire evolutionary process. The 19th-century German biologist G.J. Romanes, for example, felt that without isolation, evolution would not be possible. Another German biologist, Moritz Wagner, who corresponded at length with Charles Darwin, independently derived the notion of punctuated equilibria in the 1870s, apparently on purely theoretical grounds. Wagner saw evolution as occurring mainly in small populations isolated geographically from the large, well-established populations of the parental species. Such isolated populations, he felt, would undergo rapid evolution; if the fledgling species survived, it might grow in numbers and expand its range—in which case, Wagner surmised, further evolution of that species would grind to a halt?
How does one account for all of this incredible diversity? The answer that scientists have come to, and have since reinforced with each new discovery, is that all of this variety is the outcome of evolutionary processes. All living things are interrelated; all have descended over time from one or a few common ancestors. Charles Darwin (1808-1886) called this process descent with modification, and the phrase still accurately describes what scientists today technically call macroevolution.
Evolution Essays 2002 - SASindex
The hypothesis that an evolutionary process of variation and environmental adaptation accounts for these phenomena has been repeatedly tested and confirmed. Geographical isolation and adaptation (see below) provides one of the strongest kinds of evidence for macroevolution.