Complexity allows organisms to adapt to environmental change

A new study has revealed that instead of decreasing an organism’s ability to adapt to environmental changes, complexity in fact boosts it.

University of Michigan and Taiwan's National Health Research Institutes researchers that complexity can, indeed, develop through evolutionary processes and best equips organisms to adapt to environmental change.

The study focused on a genetic phenomenon called pleiotropy, in which a single gene affects more than one trait. Pleiotropy is important in development, aging and many evolutionary processes but is difficult to measure, and its general patterns are poorly understood, said Jianzhi "George" Zhang.

Zhang and co-workers analysed several large databases that catalogue the effects of specific genetic mutations on traits in model organisms (yeast, roundworms and mice). Each data set included hundreds to thousands of genes and tens to hundreds of traits.

The team found that most genes affect only a small number of traits, while relatively few genes affect large numbers of traits. They also found a "modular" pattern of organization, with genes and traits grouped into sets. Genes in a particular set affect a particular group of traits, but not traits in other groups.

In addition, the researchers learned that the more traits a gene affects, the stronger its effect on each trait.

Fisher, who first wrote about the cost of complexity, argued that random mutations are more likely to benefit simple organisms than complex organisms.

According to evolutionary geneticist H Allen Orr, even if a mutation benefits a complex organism, it's unlikely to spread throughout the whole population and become "fixed."

Although Fisher's observation still holds, reversing Orr's assertions minimizes its impact, thus reducing the cost of complexity.

"This means a simple organism is not best, and a very complex organism is not best; some intermediate level of complexity is best in terms of the adaptation rate," Zhang said.

“Admittedly, there were some theoretical difficulties in explaining the evolution of complexity because of the notion of the cost of complexity, but with our findings these difficulties are now removed."

The findings will be published online in the Proceedings of the National Academy of Sciences during the week of September 27.