A Shetland Wren, Troglodytes troglodytes zetlandicus, Kergord, Mainland, Shetland
Photo credit: Dr Michał Jezierski
Creationists will continually demand evidence for evolution being observed, then, when the evidence is provided, immediately insist that science should adopt their childish parody of evolution, in which one species turns into an unrelated species in a single miraculous event. That is not evolution as any biologist understands it. In fact, if such a thing were ever observed, it would falsify the Theory of Evolution, not confirm it.
By demanding evidence for something no scientist has ever claimed happens, creationists imagine they are somehow refuting science, or at least providing a plausible anti-Darwin argument for people who do not understand the science.
So this example of evolution in living populations will almost inevitably be dismissed by creationists using that same disingenuous tactic. It is evidence for the evolution of island gigantism in isolated populations of the wren, Troglodytes troglodytes, on Scottish islands. And, to rub salt in creationists' wounds, it is not merely a single isolated example, but multiple examples of gigantism evolving in island environments — an example of parallel evolution in response to similar environmental pressures acting on different local populations.
In other words, this is not some local curiosity that can be waved away as a one-off oddity, but the predictable result of isolation, restricted gene flow and similar island conditions acting on related populations. The evidence has just been published, open access, in the Evolutionary Journal of the Linnean Society by researchers led by the University of Birmingham.
The researchers, led by Dr Michał Jezierski, examined four subspecies of island wren, each isolated on a specific Scottish island or archipelago — Shetland, Fair Isle, the Outer Hebrides and St Kilda. Each of these subspecies is geographically isolated, yet exposed to broadly similar island environments, and each differs significantly from the wrens found throughout mainland Britain and continental Europe.
The study showed that the wrens of St Kilda and Shetland show little evidence of interbreeding with the mainland population. These two populations have evolved spectacular island gigantism: a wren from England will typically weigh about 7–10 grams, while a St Kilda wren weighs about 13–16 grams. The largest St Kilda wrens are therefore more than twice the weight of the smallest mainland wrens, and their genetic distinctiveness is so marked that the researchers say they may be on the way to becoming separate species.
Importantly, the genomic evidence shows that the Shetland and St Kilda wrens are genetically distinct from each other, despite having evolved similar enlarged body sizes. In other words, the same broad evolutionary outcome has arisen independently in separate island populations, rather than being inherited from a single already-giant ancestor. That is exactly what evolutionary biology predicts: related populations, isolated in similar environments, can be shaped in similar directions by similar selection pressures, even when the detailed genetic route differs.

































