New Traits Evolve for No Reason: The Study of Exaptations

Species constantly adapt and evolve, developing new traits and features over long periods of time. Yet scientists have long wondered exactly how these new traits emerge. Now, researchers have taken a closer look at these traits in order to find out how they might have been created.

There are two types of traits. Adaptations develop to address a specific need. Exaptations, in contrast, develop as a by-product of another features with minor or no function. For example, feathers may have helped insulate or waterproof dinosaurs and were only later used by birds for flight. Yet how common such pre-adaptive traits are to adaptive traits is unclear. In order to find out a little bit more about these features, researchers studied the chemical reactions taking place in an organism's metabolism.

The researchers essentially sped up the evolutionary process by working with E. Coli. The particular strain that they used could survive on glucose as its sole carbon source. The researchers then subjected this complex metabolic process to a "random walk" through a set of all possible metabolisms; they added one reaction and then deleted another from it with each step.  Every few thousand of these steps, the researchers analyzed the metabolism's reactions.

In the end, the scientists discovered that most metabolisms were viable on about five other carbon sources, including sugars, building blocks of DNA or RNA or proteins, that are naturally common but chemically distinct compounds. The researchers then confirmed the viability on these other carbon sources wasn't a natural consequence of viability on glucose by testing metabolisms on 49 other carbon sources.

"We observed an incredible abundance of viability on carbon sources that these metabolisms were never even required to use," said Andreas Wagner, one of the researchers, in a news release.

The findings seem to indicate that the traits that we see now may have had neutral origins that sat latent for generations before spreading through populations. In fact, it's possible that even complex traits like color vision could have started in this way. This research has important implications for the study of evolution and how scientists think about selective advantage.

The findings are published in the journal Nature.