Several newspapers today carry a story about genetic changes in mice. The basic issue is that species of mice common in europe have cross-bred with a species of Algerian mouse. This is of interest because the Algerian mice have a genetic resistance to many types of poison.
A commonly used poison on rodents is warfarin. You may remember it being mentioned in GCSE – it is an anticoagulant; this means it can prevent blood clotting. In high concentrations it kills mice and rats by causing excessive bleeding, but some populations are becoming resistant to it. This was identified back in the 1960s, and is a good example of how rapidly animals can evolve.
Returning to the Algerian mice, the warfarin resistance (and other rodenticides) is common in this species. The interesting part is that two different species of mice have potentially interbred to produce viable offspring. If you remember how we defined species as organisms that can breed to produce fertile offspring, how is it possible that two different species can interbreed? The answer is that our definition of ‘species’ is too simple (for example, what about species that don’t reproduce sexually?) and that genes can be passed between different species quite regularly, known as horizontal gene transfer. It is however more commonly observed in plants and bacteria rather than animals. Some scientists suggest that it may be more common in animals than we suspect, particularly in marine animals. Scientists have identified genes crossing between phyla (e.g. fungi to animals) as well.
What does all this mean for you? Apart from showing evolution in action, it is a nice reminder that very often in biology things are a little more complicated than they may first appear, and things don’t always fit into neat boxes as we may like.