A new theory proposed by two computer scientists suggests that animals can still experience significant evolutionary changes over time, even in the absence of selectional pressures.
Image: "Practice Run" by Grégoire Bouguereau.
Evolutionary potential, or what’s simply called evolvability, is a crucial attribute for a species to have. If the opportunity for physical mutations is limited or constrained, it can be exceptionally difficult for a species to adapt to its ever-changing environment.
Traditionally, evolvability has been linked to selectional pressures and the endless struggle for organisms to adapt. This notion basically says that it’s the ongoing presence of competition that spurs evolvability — that animals become increasingly capable of evolving as a response to these pressures (like competing for food, habitat, etc).
But researchers Kenneth Stanley and Joel Lehman say this isn’t the whole story, and that evolvability can increase without the pressure to adapt. By using a computer model to simulate the flow of evolution, they witnessed increasing evolvability without having to introduce competition into the mix.
Image: Evolvability heat map for the abstract model with limited capacity niches: "The average evolvability of organisms in each niche at the end of a simulation is shown. The lighter the color, the more evolvable individuals are within that niche. The overall result is that...evolvability increases with increasing distance from the starting niche in the centre." Credit: Lehman and Stanley.
What their models showed was that evolvable organisms separate themselves naturally from less evolvable organisms over time by becoming increasingly diverse.
They theorize that, if evolvability is heritable, then an unbiased (or passive) drifting process can still occur across a species — one that still pushes it towards evolvability. The reason, they say, is that evolvable organisms spread more quickly through the space of all evolutionary possibilities (i.e., more “experimentation” leads to more opportunities for adaptation). So, in order for new species to emerge in the future, it helps to be descended from those who were evolvable in the past. Thus, evolvable species accumulate over time — even without the need to adapt.
Fascinatingly, their simulations revealed that, because highly evolvable species spread more quickly, they also tend to spread to different ecological niches. And in fact, this is a good evolutionary strategy; evolvability correlates nicely with distance to original ecological niche. Niche founders, therefore, are more evolvable on average.
The timing of this paper is interesting given that Alex Wissner-Gross just posited his Maximum Causal Entropy Production Principle — the idea that intelligent behavior spontaneously emerges from an agent’s effort to ensure its freedom of action in the future. Though Stanley and Lehman aren’t talking about intelligence per se, their paper suggests that evolvability may be favored as a way to ensure future evolutionary options (i.e., the tendency is for species to maintain a certain degree of evolvability so as to not paint itself into an evolutionary dead-end).
Read the entire study at PLOS One: “Evolvability Is Inevitable: Increasing Evolvability without the Pressure to Adapt.”