Where do new species come from?
Bert asks, 'How do new species come about? How do they expand from one or two individuals to become an established species without falling victim to inbreeding problems?'
James Tytko took this question with the help of Professor Roger Butlin...
Roger - There are various different ways in which new species can form, either where one population gets isolated, usually geographically, and diverges. And the other option is essentially where one species occupies two different environments and natural selection adapts different populations within the species to different environments.
James - At what definitive point do you say that you've got a brand new species?
Roger - That is difficult. A classic example of this would be Darwin's finches in the Galapagos Islands. The islands formed volcanically and so a new habitat was created and then a few individuals colonised those islands from the South American mainland. And for many generations after that, they had no contact with the mainland. And so they evolved independently on the islands. And actually smaller populations evolved independently on different islands, eventually forming multiple different species on on the Galapagos.
James - And the other way new species can form is a case of populations living in the same place, but beginning to diverge to gain an advantage in the different habitats in that close geographical proximity.
Roger - Another form of speciation would be like in the coastal snails that we study, where some populations of the snails live in boulder field habitats (where there are lots of crab predators) and other populations live on rocky headlands where there are very few predators, but there's very strong wave action. So those populations are selected to adapt in different ways. When they're exposed to predators, they grow large with thick shells. And when they're exposed to wave action, they grow small with thin shells.
James - What's the advantage of the small thin shells on the rocks?
Roger - They're more streamlined and less likely to be dislodged by waves. They can also hide in crevices on the rocks.
James - And the bigger shells on the shore make it harder for the predators to break into them. That makes a lot of sense. But in that divergent case, is it right then that animals who start to develop new traits continue to breed with other animals as they evolve? It's more often a very gradual process and that's why it's hard to point to an exact generation where we can say we are defining a new species now.
Roger - Yes, that's right. It's a gradual process. And often perhaps when a few individuals arrive in a new environment, like the Galapagos Islands, the population was able to grow very quickly. There were lots of resources and few competitors and, because of that, the inbreeding problems were not so serious.