Mimicry in Butterflies Is Seen here on These Classic “Plates” Showing Four Forms of H. numata, Two Forms of H. melpomene, and the Two Corresponding Mimicking Forms of H. erato.
Source - Repeating Patterns of Mimicry. Meyer A, PLoS Biology, Vol. 4/10/2006, e341 doi:10.1371/journal.pbio.0040341, CC BY 2.5, Link
The great day creationists have been assuring themselves is imminent — and have been doing so for at least half a century — when evolutionary biologists finally announce that they have abandoned the Theory of Evolution because it fails to explain the evidence, seems to recede even further with almost every new research paper. Instead of being replaced by creationism, complete with unproven supernatural entities, magic, “unknowable mysteries” and evidence-free Biblical folklore treated as real history, evolution remains the basic framework within which modern biology makes sense of the evidence, formulates hypotheses and interprets results.
Almost invariably, research that appears at first sight to question some aspect of evolution is doing nothing of the sort. It is refining the details. That is the case with a new paper in PLOS Biology by a team led by scientists at the University of York, the University of Sheffield and the Wellcome Sanger Institute, which suggests that, in some circumstances, evolution may be more predictable than a simple caricature of random mutation filtered by natural selection would lead us to expect.
The team analysed the genomes of seven species of Ithomiini and Heliconius butterflies, together with the day-flying moth Chetone histrio. These lineages diverged between about 1 million and 120 million years ago, yet they have evolved remarkably similar wing colour patterns as members of neotropical mimicry rings. These warning patterns signal to predators that the insects are toxic or distasteful, so different species benefit by converging on similar “do not eat me” designs.
What the researchers found was striking. In several butterfly lineages, similar colour-pattern switches were associated with the same two genes, ivory and optix. More precisely, the important changes were not usually in the protein-coding parts of those genes themselves, but in nearby regulatory regions — the genetic switches that determine when and where those genes are turned on and off during wing development. In other words, natural selection has repeatedly arrived at similar visible results by acting on the same underlying developmental toolkit.
This is not evolution being refuted; it is evolution being understood in greater detail. What looks like simple convergence from the outside turns out, at the genomic level, to be a repeated use of the same limited set of viable routes. Evolution is still contingent, still dependent on mutation, recombination, selection and inheritance, but it is not infinitely free to do anything at all. Developmental systems constrain what variations are available, and those constraints can make some evolutionary outcomes more likely than others.
One particularly awkward aspect for creationists such as Stephen Meyer, who insist that new “information” must be intelligently inserted by some unknown mechanism, is that the study shows how major changes in form and appearance can arise from changes in the regulation and arrangement of existing DNA. In the moth Chetone histrio, colour-pattern variation is associated with a large inversion — a section of DNA flipped in orientation — closely resembling the inversion-based “supergene” architecture seen in one of the co-mimetic butterflies, Heliconius numata. No designer is required; ordinary genomic processes, filtered by selection, are enough.
It is also worth noting the timescale. These same genetic routes appear to have been available to lepidopterans since deep in the Mesozoic, around the time of the dinosaurs. The predators, environments and ecological communities have changed enormously since then, but the evolutionary principle remains the same: when similar selective pressures act on organisms with similar developmental machinery, evolution can repeatedly find similar solutions.
































