Evolution can make amazing changes; For example, today’s flying songbirds are descended from terrestrial, wingless dinosaurs that roamed the earth millions of years ago; But some organisms seem to experience very little change even over very long periods of time. Silicate fish is one such creature that resembles its 410 million-year-old fossil counterparts.
Scientists have long wondered how these species resist the pressures of natural selection. The prevailing hypothesis to explain this “paradox of stagnation” has been that sometimes natural selection selects common or average traits in some species instead of selecting more unusual traits that cause species to change and keeps them unchanged. This event is so calledStable choice” is named.
But a study recently published in the Proceedings of the National Academy of Sciences argues against the idea of stabilizing selection. According to this study, evolution permanently favors various traits in seemingly immutable animals that It improves their short-term survival. James Stroud“However, in the long run, all that evolution is neutralized and no change happens,” says the study’s lead author and a biologist at the Georgia Institute of Technology.
Stroud and his colleagues studied 4 species of anole lizards. All of these lizards lived relatively unchanged for 20 years on a small island at Florida’s Fairchild Tropical Botanical Garden. The researchers trapped the members of this population for 3 years and every 6 months. They measured the head size, leg length, height, and weight of each lizard, as well as the size of their sticky claw pads, and determined which species survived.
Stroud expected to see consistent selection maintaining similar traits; But instead he saw clear evidence of directional selection. Some lizards, with unique features such as webbed toes, survived better in the short term than others. However, in each generation, the “best” features changed; For example, in some years long legs helped survival and in others shorter legs were better.
The direction and strength of selection in lizards fluctuated so much that sometimes there was no clear pattern. Rosemary Grant“Such changes are likely to occur on a microscale without net directional change,” says evolutionary biologist at Princeton University.
Because the study shows that natural selection favors more unusual traits over average traits from year to year, its results do not support the theory of stabilizing selection. Tadashi Fukamian ecologist who studies evolution at Stanford University, says the results instead provide a good explanation for why we see what we think is stabilizing selection.
Many new features are evolving in the short term; But they do not offer a significant advantage in the long run. In other words, quiescent species may simply have found the best possible combination of traits for sustained success in their environment.
Now the question arises, what happens when the environment around a resident species changes dramatically? To find the answer to this larger question, Stroud continues to travel to Florida to track more generations of lizards.
