While Charles Darwin believed that the process of evolution occurred over a geological timescale, we have seen examples of dramatic adaptive evolution occurring over only a handful of generations. How fast is development?
In adaptive evolution, natural selection leads to genetic changes in traits that promote the survival and reproduction of individual organisms. While Charles Darwin believed that the process occurred across geological time scales, we have seen examples of dramatic adaptive evolution over only a handful of generations. Moths change color in response to air pollution, overfishing has caused some elephants to lose their tusks, and fish have developed resistance to toxic chemicals.
However, it is still difficult to say how fast adaptive evolution is currently. Nor do we know whether it played a role in the fate of populations faced with environmental changes.
To measure the rate of adaptive evolution in the wild, Scientists have studied 19 groups of birds and mammals over decades† They found that they evolved two to four times faster than had been suggested in previous work. This demonstrates that adaptive evolution can play an important role in how traits and populations of wild animals change in a relatively short period of time.
How do you measure the speed of development?
How do we measure how quickly adaptive evolution occurs? According to the “fundamental theory of natural selection”, the amount of genetic variation in the “ability” to survive and reproduce between individuals in a population also corresponds to the degree of adaptive evolution of the population. This basic theory has been known for 90 years, but it has proven difficult to put into practice. Attempts to use the theory in wild populations have been scarce and plagued by statistical problems.
The authors of the new study collaborated with 27 research institutions to collect data from 19 long-tracked wild populations, some since the 1950s. Generations of researchers have collected information about the birth, mating, reproduction, and death of every individual in these populations. Together, this data represents about 250,000 animals and 2.6 million hours of fieldwork.
Then they used quantitative genetic models to apply the “basic theory” to each group. Instead of tracking changes in each gene, quantitative genes use statistics to capture the net effect that comes from changes in thousands of genes.
Offspring are on average 18.5 percent “better” than their parents
The researchers also developed a new statistical method that fits the data better than previous models. Among the 19 groups, they found that genetic change in response to selection was responsible, on average, for an 18.5% increase per generation in individuals’ ability to survive and reproduce.
This means that the offspring are, on average, 18.5% “better” than their parents. In other words, the average population can withstand the degradation of its environment by 18.5%. (This may change if the genetic response to selection is not the only influencing factor; more on that below.)
Looking at these rates, scientists have found that adaptive evolution reflects the most recent changes in the properties of wild animals (such as size or timing of childbearing). Other mechanisms are also important, but this is strong evidence that evolution must be viewed in tandem with other explanations.
What does this mean for the future?
What does this mean for the future? will evolution the animals Helping to adapt at a time when natural environments around the world are changing dramatically due to climate change and other forces?
Unfortunately, this is where things get tricky. The study only looked at genetic changes caused by natural selection, but in the context of climate change, other forces are at play.
First, there are other evolutionary forces (such as mutations, chance, and migration). Second, environmental change per se is probably a more important driver of population demographics than genetic change. If the environment continues to deteriorate, the theory tells us that adaptive evolution in general will not be able to compensate fully.
Finally, adaptive evolution itself can change the environment in which future generations live. In particular, when individuals compete with each other for a resource (such as food, territory, or mates), any genetic improvement will lead to increased competition among the population.
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