Why is life so variable?

When you look at the people around you, or even the animals and plants, it is obvious that they are a hugely varied bunch.  For evolutionary biology, this is a puzzle: if one type of gene has features that make individuals carrying it more likely to survive and reproduce, that gene will tend to be passed on more often and will replace all the alternative forms: this is natural selection.    But if selection reduces genetic diversity, why is nature so variable?  

One possible answer is that variation in the environment might mean that different traits are favoured in different years.  This would mean, there are no ‘better’ genes, some genes are good in some years, and other genes are good in other years.

To see if this fluctuation in selection occurs in nature, we used 8 years of our observational data, and each year we used DNA fingerprinting to count how many offspring each cricket had.  This revealed substantial variation among years in how important particular traits are for individual reproduction.  Most convincingly; in some years, crickets that became adult earlier had more offspring, whereas in other years crickets that emerged early had fewer offspring.  This could be the smoking gun that shows that variation in the environment can maintain variation – genes for emerging early and late co-exist because which of them is better, varies among years.


Read our paper on this work here