Saturday, 6 August 2016

Watching Evolution in Florida!

Study spots evolution in action in Florida bird | Science | AAAS

It's become something of an online ritual; almost a religious rite. Creationists come bursting into a debate group and announce confidently that evolution has never been observed and then they get given several examples of observed instances of evolution. Then they declare that that wasn't evolution and insist evolution is something unrecognisable as the scientific theory of evolution or the observable phenomenon the theory seeks to explain.

It's the equivalent of someone posing as an expert on geometry and claiming there is no such thing as a circle, then, when shown a circle, declaring that a real circle should have a circumference to radius ratio of exactly 3 because the Bible says so.

So, it's with these science deniers in mind that I bring this lovely example of observed evolution to the attention of my readers - evolution being change in allele frequency over time. It involves a study of a small, sedentary population of Florida scrub jays (Aphelocoma coerulescens) over 45 years. It was prsented to the recent Biology of Genomes meeting in Cold Spring Harbor, New York, USA. The study was made possible by recent advances in genetic sequencing.

The beautiful little Florida scrub jay is unusual in that juveniles often stick close to 'home' and help raise the next brood. They are also remarkably sedentary, rarely straying more than 10 kilometres from where they were raised. This has made it relatively easy for researchers at Archbold Biological Station in Venus, Florida to build a detailed family tree over 12 generations - 3800 birds in all. According to the report in Science:

[The researchers] have been able to build a detailed family tree for jays there that spans 12 generations. And for the past 45 years, they have kept records on the life span, number of eggs and offspring produced per year, and other traits; they’ve also taken blood samples from every member of the group over the past 25 years.

By comparing 15,000 locations in the genomes of all 3800 birds to the full genome of a reference bird, Nancy Chen, a population genetics fellow now at the University of California, Davis, found that the vast majority of changes were neutral but 67 locations showed adaptive variation. Further analysis has identified 21 locations that appear to help female jays live longer and 4 locations affect which sperms are successful at fertilising eggs. Some variants were differentially passed on to the next generation more frequently than other giving change in allele frequency over time.

The study also gives insight into why, when we might expect the 'best' variant to quickly become the only variant, we often see different variants being retained over time. It seems that some variants may only give an advantage at particular points in the life cycle with others being more important at different times. The selection pressure is then to retain this genetic variation within the population. This genetic diversity in turn makes the species more responsive to environmental change.

So, with this nice example of observed evolution over 12 generations in the same population of Florida scrub jays we can confidently predict now that creationists will declare this not to be evolution after all because the scrub jays didn't turn into humans or owls, or something equally idiotic. At all costs, a good creationist must never accept the evidence that evolution happens, because their entire faith would come crashing down around them and they wouldn't feel important enough.

Incidentally, I wonder how many creationists spotted that the vast majority of genetic changes were neutral, not detrimental as their creationist dogma insists all mutations must be.

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