Traditionally scientists have thought that evolution occurs very gradually with perhaps some occasional (relatively) rapid changes. The fossil evidence certainly suggests a gradual process and it makes intuitive sense because genetic shifts in populations require generational changes. But more and more scientists are concluding that evolution occurs very, very rapidly as a rule.
Wherever biologists look closely, they are seeing populations in which evolution is occurring right now, not static populations that are simply waiting for some sort of pressure to force them to start adapting. Accepting that evolution occurs rapidly, though, will require a change in how evolution itself is understood.
Reports of rapid evolution go back a surprisingly long way. It turns out that British entomologist Albert Farn wrote to Darwin in 1878 to point out that darkly coloured annulet moths were becoming more common than lighter moths in areas blackened by pollution (Current Biology, vol 20, p R95). This was nearly 20 years before it was first suggested that the famous peppered moths were turning black for the same reasons.
In 1897, it emerged that several insect populations were becoming resistant to insecticides. By the 1930s, more examples had surfaced, such as scale insects developing resistance to hydrogen cyanide.
Over the following decades, biologists stumbled upon more and more examples. A few became famous, such as the peppered moth, but all were regarded as curiosities. "People went, 'wow, that's amazing, that must be the exception'," says Michael Kinnison of the University of Maine in Orono, one of the first researchers to set out specifically to look at evolution in action.
Today, there are probably thousands of examples, and a growing number of biologists think that far from being an exception, rapid evolution is common. "Wherever people look for it, it's there," says Kinnison. "Very fast change can occur in very short periods." And thanks to advances in genetics, we are beginning to understand how it is possible.
Source: New Scientist, April 2, 2011
As more examples of rapid evolution are turned up, the more we'll have to face concluding that it may be the "norm" rather than the exception. It probably shouldn't be too surprising because the slower evolution is, the harder it will be for life to adapt to changes in the environment. Rapid evolution has a lot of benefits.
And contrary to what Evolution Deniers insist, this isn't just about shuffling around existing genetic diversity. Rapid evolution also includes the development of new genetic mutations that aid in survival. What's more, it also means the development of entirely new species -- again, contrary to the ideology of those in denial about evolution.
While rapid evolution usually involves existing mutations, new ones can play a role too. For instance, the mosquito Culex pipiens evolved resistance to organophosphate insecticides when an unusual mutation produced several copies of one gene, enabling it to make more of an enzyme that could break the pesticides down. This new mutation has spread worldwide (Nature, vol 350, p 151).
In the right circumstances, even new species can evolve in next to no time. In 1866, farmers in the US reported that an unknown maggot was attacking their apples, a crop introduced two centuries earlier. Entomologist Benjamin Walsh suggested that the "apple maggot" was a strain of the native hawthorn fly that had switched diets. Walsh had previously suggested this kind of process could lead to speciation.
We now know that Walsh was right. Genetic studies have shown that the hawthorn fly appears to be in the process of splitting into two species (Annual Review of Entomology, vol 47, p 773). What's more, the parasitic wasps whose larvae feed on the maggots are also splitting into two species (Science, vol 323, p 776).
More examples keep turning up. A species of fish in a lake in Nicaragua has split in two in only 100 years. The new variety has evolved a narrower, pointier head and fatter lips, ideal for nibbling insects from crevices. The original variety has sturdier jaws and extra teeth to crack snail shells. Lab studies suggest the strains do not mate with each other even when put together, which would mean they are on their way to becoming separate species.
So why does evolution appear to be so slow over the long term? It may be that rapid shifts in one direction then in another direction seem to disappear when viewed over a long time period. The fossil record provides us with just a small sample of everything that's lived and, what's more, may only be providing us with something akin to the "average", such that any extreme shifts that occur in shorter time periods are cancelled out.
Put it all together and the picture of evolution that is emerging is radically different to the way most people envisage the process. As Kinnison puts it, the popular view of evolution is upside down. People think evolutionary changes are imperceptible in the short term but add up to big changes over millions of years. In fact, the opposite is true. It now appears that organisms evolve very rapidly in response to any changes in their environment, but in the longer term most evolutionary changes cancel each other out.
So the longer the period you look at, the slower evolution appears - a phenomenon first pointed out in 1983 by Philip Gingerich of the University of Michigan, Ann Arbor (Science, vol 222, p 159). At the time nobody believed it, but "people have recognised now that it was a very insightful piece of work," says Hairston.
"I think a superficial reading of the fossil record has given us a misleading picture of the evolutionary process," says Gingerich. "The changes seen over long intervals of geological time are not representative of what happens on a generation-to-generation timescale."
This is especially true of long periods with little or no evolutionary change. The conventional explanation for this stasis has been that evolution is usually slow because selection is usually weak. "But this is perfectly consistent with strong selection, providing it fluctuates," says Graham Bell of McGill University in Montreal, Canada.
Assuming it is right, this new picture of evolution should perhaps come as no surprise. We have always known that the "march of progress" is an illusion, that evolution is a random process with no purpose. Rather than going somewhere slowly, evolution usually goes nowhere fast.
I'm sure that there is still a lot about evolution that we don't understand yet, but one thing seems clear: every time we do learn something new about evolution, the less compatible it becomes with traditional western theism and theistic religion. Apologists keep trying to match their religious ideology to whatever science is discovering, but that's a losing game in the long run. If religious apologists had any legitimate claim to independent knowledge or facts, they wouldn't have to keep reinterpreting their texts and traditions.