Speaking as both part lettuce and half banana, I would like to add that the background to evolution in the northern and southern temperate zones is influenced by two important factors; cyclic climate change and specie extinctions.
During the past 2,6 million years there have been on average a recurring cycle of about 100,000 years repeating typically this succession of climates: very cool for most of say 50,000 years punctuated with an arctic "or "glacial" episode followed by very cool and then warming up to the mild "interglacial" which we have been experiencing for the last 10,000 years. This may last another ten thousand, maybe more maybe less. These cyclic episodes alter the ecology of the various geographical regions and habitats and put stress especially on the ability of mammalian inhabitants to keep the same populations breeding.
It came as a surprise to me to learn that during the last cool episode leading up to and including the last glacial, that in North America were lost something like 75% of all large mammals. For example mammoth, mastodon, glyptodon (giant armadillo) giant beaver and six of the seven species of bison, camelops, big cats and short faced bears. The extinctions allow for new species to evolve by the vacant ecological niches available to be exploited. There is a rule that the larger the mammal the fewer the generations they survive. Squirrels have been around for about twenty million years but woolly mammoths only from 250,000 years ago to 4,000. Extinctions can be sudden but speciation (arrival of new species) is only apparent over geological time.
Incidentally, doing palaeontology and archaeology were things I put on hold when I became a JW as a young teenager. So it was with great pleasure after leaving the cult, that I joined a university group and helped dig up many mammoths (Mammuthus primigenius) as well as a few straight tusked elephant (Palaeoloxodon antiquus) here in Oxfordshire, England.
