Washington: Although it`s a constant and sometimes rapid process, evolutionary changes takes one million years, say scientists.
A new study, published in the `Proceedings of theNational Academy of Sciences` journal, combined for the first time data from short periods such as 10 to 100 years with much
longer evidence found in fossil record over millions of years.
It determined that rapid changes in local populations often don`t continue, stand the test of time or spread through a species.
In other words, just because humans are two or three inches taller now than they were 200 years ago, it doesn`t mean that process will continue and people be two or three
feet taller in 2,000 years. Or even as tall in one million years as we are now, say the scientists.
"Rapid evolution is clearly a reality over fairly short time periods, sometimes just a few generations," said lead author Josef Uyeda of Oregon State University.
"But those rapid changes do not always persist and may be confined to small populations. For reasons that are not completely clear, the data show the longterm dynamics of evolution to be quite slow," he added.
Across a broad range of species, the study found that for a major change to persist and for changes to accumulate, it took about one million years.
"What`s interesting is not that we have so much biological diversity and evolutionary change, but that we have so little. It`s a paradox as to why evolution should be so
slow," Uyeda said.
Long periods of little change, Uyeda said, are called "stasis", a pattern that originally led to the concept of "punctuated equilibrium", controversial when it was first
proposed in the early 1970s.
This study supports the overall pattern of stasis and punctuational change. However, Uyeda says that there may be different causal mechanisms at work than have often been
Uyeda said: "We believe that for changes to persist, the underlying force that caused them has to also persist and be widespread. This isn`t just some chance genetic mutation that takes over.
"Evolutionary adaptations are caused by some force ofnatural selection such as environmental change, predation or anthropogenic disturbance, and these forces have to continue and become widespread for the change to persist and accumulate. That`s slower and more rare than one might think."