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High Speed Evolution
Taco Cowboy writes: Normally, the term "evolution" implicitly refers to super-long time frames. However, in the case of lizards on Florida islands, evolution seems to have shifted into a higher gear. Researchers have documented noticeable changes in a native species over a period of just 15 years, after an invading species altered their behavior (abstract). "After contact with the invasive species, the native lizards began perching higher in trees, and, generation after generation, their feet evolved to become better at gripping the thinner, smoother branches found higher up. The change occurred at an astonishing pace: Within a few months, native lizards had begun shifting to higher perches, and over the course of 15 years and 20 generations, their toe pads had become larger, with more sticky scales on their feet.
'We did predict that we'd see a change, but the degree and quickness with which they evolved was surprising,' said Yoel Stuart, a postdoctoral researcher in the Department of Integrative Biology at The University of Texas at Austin and lead author of the study... 'To put this shift in perspective, if human height were evolving as fast as these lizards' toes, the height of an average American man would increase from about 5 foot 9 inches today to about 6 foot 4 inches within 20 generations — an increase that would make the average U.S. male the height of an NBA shooting guard,' said Stuart."
'We did predict that we'd see a change, but the degree and quickness with which they evolved was surprising,' said Yoel Stuart, a postdoctoral researcher in the Department of Integrative Biology at The University of Texas at Austin and lead author of the study... 'To put this shift in perspective, if human height were evolving as fast as these lizards' toes, the height of an average American man would increase from about 5 foot 9 inches today to about 6 foot 4 inches within 20 generations — an increase that would make the average U.S. male the height of an NBA shooting guard,' said Stuart."
If you kill the shortest third of all humans, the average height goes up immediately within the current generation.
If construction was anything like programming, an incorrectly fitted lock would bring down the entire building...
The average height of post-war (WWII) Japanese was 2 inches taller than the previous generation. and that was due merely to the better availability of food--an environmental factor--but probably not anything to do with evolution per se.
As stated in another post, if you kill off the shortest 1/3 of the population, the average height immediately goes up.
Similarly, if the small-footed lizards drop off the trees and can't find enough food, the average foot-size immediately increases in the population independent of evolution occurring. Evolution is 2-step process. The environmental advantage or disadvantage occurs during the individual lives of each member of the species. The passing of genes to the next generation is a separate process that still reshuffles the genes via sex relentlessly regardless of environment. That's what makes it hard to determine when evolution via genes is occurring vs purely environmental factors winnowing a current population. The new population of lizards still produces some amount of small-footed ones due to sexual mixing of genes--and if the environment changes to reward smaller feet, the population will again change quickly.
I don't know why the researchers were so surprised by this. If the genetic variation already exists within the population under selective pressure, then the "evolution" measured by phenotypical changes in the population can take place literally overnight. Kill every human under 6'4" and the population will be 6'4" from then on, especially if you don't return to the set of selective pressures that had encouraged the shorter average. Sure there will be a lot of shorter individuals being born at first, but they'll fall to the same new selective pressure that killed the initial short cohort. This is exactly how the famous peppered moth evolution event happened so quickly; it wasn't anything unusual about the moth species in question, just a quick change in the suitability of existing genes. Evolution is only slow when the locally optimal genes don't exist in the population, and need to arise by mutation or genetic flow, or when an immediate optimum has room for genetic fine tuning, so to speak. TFA isn't really an example of evolution per se, it's an example of natural selection--a closely related concept in that they almost always co-occur, but it is not the same thing. We've changed the equilibrium frequencies of various genes, but as far as we know there are no new genes in this population. (And as far as that goes, it's a decent illustration of the importance of genetic diversity in a population: this population would be extirpated if it didn't have the genes responsible for these behavior and phenotype changes.)