TECHNION RESEARCHERS QUESTION RANDOMNESS IN EVOLUTION THEORY

Researchers at the Technion Israel Institute of Technology have published a study challenging the assumption that evolution proceeds randomly once organisms reach equal levels of fitness. The study, published in the journal PNAS, examines what happens when different traits arrive at the same point on an evolutionary "fitness landscape", a situation biologists call degeneracy. Biologist Naama Brenner, one of the study's authors, said evolution is usually described as organisms climbing fitness peaks to become better adapted to their environment, but that organisms sometimes face several paths yielding the same fitness level, raising the question of how evolution selects between them. The researchers said evolution does not generally wander randomly among these equally fit options.

To test this, the researchers built a simplified mathematical model of populations evolving on flat, degenerate fitness landscapes. The model incorporated the natural selection and mutation processes seen in real populations. They used it, along with further simulations, to trace how populations behaved across hundreds of generations. Fitness landscapes are commonly pictured as containing peaks representing traits best suited to survival, with many species able to reach the same peak by different routes.

The study found that organisms reaching maximum fitness continued moving across the landscape towards its flattest point, a movement that offered no additional fitness advantage, the researchers said. This pattern held consistently across the simulations the team ran over hundreds of generations. The findings suggest that movement among equally fit evolutionary outcomes follows a more structured direction than the random model long assumed in biology, according to the study. Brenner and her co-authors said the results raise new questions about how evolution selects between paths of equivalent fitness.