Geographic Distribution of Related Species

• Another clue to patterns of past evolution is found in the natural geographic distribution of related species, it is clear that major isolated land areas and island groups often evolved their own distinct plant and animal communities
• Land mammals were entirely absent from the even more isolated islands that make up Hawaii and New Zealand, each of these places had a great number of plant, insect, and bird species that were found nowhere else in the world
• Likely explanation for these mostly unique biotic environments is that the life forms in these areas have been evolving in isolation from the rest of the world for millions of years
• Before humans arrived 60-40,000 years ago, Australia had more than 100 species of kangaroos, koalas, and other marsupial mammals but none of the more advanced terrestrial placental mammals such as dogs, cats, bears, horses