I read an interesting article in The Awake in “The Scientist” on-line magazine and I thought I would summarise it for the lovely people on JWN. This is a great example of what “survival of the fittest” really is and it provides evidence of evolution that can be observed in our own lifetimes.
Creationists will say this is “micro” evolution and not “macro” evolution (or as an evolutionary biologist refer to it – speciation). They will argue that that these are two different concepts, but the reality is that it is an accumulation of these small changes occurring in different populations that will eventually create a divergence resulting in a new species.
Charles Brown of the University of Tulsa has been studying the social behaviour of cliff swallows for the past 31 years (good job Armageddon didn’t strike in 1975). These birds are migrants that spend their summer on the pancake-flat plains of south western Nebraska.
Here they nests under bridges and overpasses. During his studies Brown has seen a lot of road kill—and whenever he spotted dead birds on the roadside, he collected them. He says there was no particular reason for this but as a keen taxidermist he didn’t want good specimens to go to waste.
But as the years passed he noticed fewer and fewer dead swallows along the roadside, which didn’t correlate with the fact that the population was increasing. Being a scientist he wondered why this was the case. Was it that the birds were adapting to road mortality? Was an evolutionary change occurring making them less vulnerable to road kill?
As part of his research Brown trapped birds in mist nets in order to weigh and perform measurements. Some of the birds trapped in these nets die, and so he had two sets of data to compare, birds killed in road accidents and those killed by netting.
He noticed that vehicle-killed swallows had significantly longer wings, and thus broader wingspans, than those that died randomly in the nets. . And while the average wing length in the population had gone down since 1982, the average wing length of birds killed on the road had increased. The results suggest that these birds are adapting (evolving) to avoid collisions with cars.
In Browns own words
“Shorter wings may confer greater manoeuvrability to help the birds evade cars—a trait that appears to have been selected for over time”
He also pointed out that the reduction in wing size wasn’t entirely because of cars, it is possible that changes in insect communities due to rising corn monoculture could also select for shorter wings. It is of course also possible that the birds are simply learning to avoid cars. But it would appear that road mortality is exerting a strong selection pressure.
Anyway, I found this interesting, maybe someone else will too!