“Researchers have documented repeated evolution in other organisms, but the sticklebacks are unique because the freshwater transition has occurred so many times. “Sticklebacks have been a phenomenal system for understanding rapid evolution,” says evolutionary biologist Erica Bree Rosenblum of the University of California, Berkeley, who wasn’t involved in the study. “This paper shows that repeated evolution can occur by ‘reusing’ the same genetic mechanisms over and over again.””
This quote is from a review in Science of a Nature paper where stickleback fish genomes were sequenced and compared. The catch is, the stickleback fish used to be a sea fish until glaciers melted 10,000 years ago and left many stranded in freshwater lakes and streams.
What then happened is that the freshwater sticklebacks all had to evolve to survive in the freshwater.
Independently.
What is interesting, is that it’s clear that all of these fish evolved the same adaptations. And now there is genetic evidence that most of these independent changes were in the same places of the genome in each of these freshwater fish.
While this has been seen in other organisms, the stickleback provide an experiment where this has happened multiple times, showing “repeated evolution can occur by ‘reusing’ the same genetic mechanisms over and over again.”
Adjacent possibles
I am not surprised.
I picked up a term from futurist Paul Saffo, “adjacent possible” (I use it a lot to point out interesting things in evolution). Applied to evolution, it means an organism can really only sample the possible mutation paths that are adjacent to its current make-up. An organism cannot evolve from bacteria to bird in one move, much like “you can’t get there from here” in one move. In both cases, each step must be an adjacent possible step.
In this case, all the sticklebacks had similar adjacent possible ways to adjust to freshwater living. So they were constrained by their genome. But also, the environment exerted similar pressures, so the adjacent possible were further constrained.
The sticklebacks all had to make the same choices, with the same starting material, to adapt to the same environment.
What do you think?
I think this is cool.
Read the review How Evolution Copies Itself – ScienceNOW.
This *is* cool 🙂
Recommend you look up ‘Where good ideas come from: the seven patterns of innovation’ too, I’ve just finished it and it has a whole chapter on the adjacent possible. I think you’ll like it.
J