What’s he building in there?
LOOK AROUND YOU. The world is brimming with the diversity of life. The great assortment of species is so much a part of our world that we take it for granted. It’s easy to say that diversity results from the theory of evolution and be done with it. But why is there such a wide gamut of life and how does diversification actually unfold? The question isn’t ‘Does evolution happen?’ but rather ‘How does evolution happen?’
When we look back in time we see that evolution has been punctuated by bursts of spectacularly rapid diversification during which many new species suddenly appeared. This process (called adaptive radiation) is very fast compared to the usually steady march of evolution, but it’s still too slow for scientific study.
Rees Kassen is the University of Ottawa’s Research Chair in Experimental Evolution. When it comes down to it, Kassen wants to know the answer to a straightforward question: Why are there so many different kinds of living things in the world?
To study the process of biodiversity, Kassen needs to watch evolution take place in his laboratory. He can do this by studying microbes. Since microbes live for only a short time, Kassen can observe changes that occur over generations in only a matter of days. This makes microbes an ideal model for studying adaptive evolution.
When Kassen places colonies of microbes in a beaker of nutrient-rich broth, the colonies choose to live at the centre where there’s the most food. Early on the colony is smooth and round. After a while, resources become scarcer and competition becomes more fierce. Some of the colonies realize that if they stop fighting for control of the centre and move to the fringes they will have an ecological niche all to themselves. And so some colonies fall to the bottom of the beaker where they evolve into brush-shaped colonies. Others rise to the top where they change into very wrinkly colonies.
The new ecosystem offers the microbes opportunities to specialize and to a certain extent determines the form of the diversity. On the other hand, it is competition for resources that drives the specialization. Kassen suspects that these two factors cause adaptive radiation to occur quickly and helps explain why diversification happens in bursts.