Friday, November 1, 2013

Speciation of butterflies

One of several pattern variations seen in
Heliconius, the butterfly genus used in the
study.  Image source.
(Credit: Marcus Kronforst)
The evidence for evolution is often claimed to be overwhelming.  However, as mentioned in my review of "Evolution vs. God," the definition of "evolution" in this case is variable.  Observational evidence points toward small-scale adaptations caused by changes in proportions of genes in a population, often termed "microevolution."  These examples are then extrapolated to support the idea of universal common descent, often termed "macroevolution."  Still, the exact relationship between micro- and macroevolution is a bit foggy to biologists.  The nodes in the family trees, where two lines branch from one, are more conceptual on a large scale and are not necessarily meant to represent a distinct point in time.  Nevertheless, it is common among scientists and non-scientists to imagine a speciation event occurring within one generation, as if a mother gave birth to two siblings, and the offspring of which eventually diverged into two distinct species, such that the two species literally had one single common ancestor (the mother).

It appears, however, that speciation might not be so clear-cut.  A group of biologists published a report yesterday explaining that extensive interbreeding does not appear to prevent diverging groups from forming two separate species.  More pertinent to this discussion, they claimed that this study demonstrates "the link between microevolutionary processes acting within species and the origin of species across macroevolutionary timescales."

For this study, the genomes of 32 butterflies from Costa Rica were sequenced and compared.  All of the butterflies were members of the genus Heliconius, which contains five species in the region.  Although these species can and do interbreed, they are thought to be diverging, eventually to the point where they are no longer interfertile.  After analyzing the genomic data, the authors concluded that genes related to wing patterns were the first to diverge, but ongoing interbreeding kept further separation to a minimum.  Over time, other differences arise, and then natural selection leads to an explosion in differentiation, resulting in two new species.  The scientists conclude, then, that interbreeding and natural selection play a sort of tug-of-war before the species finally split.

The idea of speciation is not one that creationists currently revile, contrary to popular belief, though that has not always been the case.  A few centuries ago, it was common for Christians to believe that the world and the creatures in it did not change.  The reasoning was that God does not change, so His creation should not either.  However, this line of thinking is not biblical, and it may have contributed to the original divide between science and the Bible in the eyes of society.  Once science began demonstrating that the world does change, and that creatures go extinct, people began rejecting the Bible due to the belief that such things were unbiblical.  Yet, the Bible is quite clear that the earth underwent a drastic change during Noah's Flood, and there is nothing that speaks against animals changing over time.  The "kinds" created during Creation Week were groups which were able to produce offspring with each other, but this does not guarantee that all of their offspring would be able to do so.  Even so, all of their offspring would be of the same kind.

Interestingly, the word "species" comes from the Latin for "kind" and was applied to biology because of its use in the Latin Bible.  However, the biological definition of "species" changed over time, so the two should not be equated.  Ideally, a "species" is defined as a group of organisms capable of producing viable offspring but are unable to do so with any other groups.  However, the assignment of species is not straightforward, so interbreedable organisms may still be classified as separate species (this is especially difficult with extinct creatures), particularly if they are genetically capable of breeding but simply don't for physical, geographic, or appearance reasons.  Therefore, it is still entirely possible for several species to arise from a single created kind.

So if speciation is possible, doesn't that mean evolution is true?  Well, yes and no.  By some definitions, evolution is simply "a change in gene frequency within a population," as my former ecology textbook said.  This can be observed to happen all the time and does not even require full speciation to occur.  So, in this sense, evolution is a scientifically proven, observable fact.  However, the sense of "evolution" that is supposed to link mice and men by a distant common ancestor is a different matter.  The evolutionary view is that this "macroevolution" is simply composed of many many "microevolutionary" changes accumulated over time.  Although these terms were once used widely by creationists, they have since been abandoned by the creation camp and adopted by evolutionists.  The terms "micro-" and "macroevolution" imply that the only difference between those two is a matter of scale or quantity.  The real problem, creationists say, is a matter of information and direction.  Evolution from a single cell to the great variety of life we see today would require massive amounts of information added to the genome.  However, creationists claim that all observed genetic mutations only result in constant or less information, never an increase.  Therefore, the current biodiversity could never have descended from a single cell, regardless of the amount of mutations given.  Rather, the species we see today have less variability than those that stepped off of Noah's Ark, because information was only lost over time.  Evolutionists refute these claims with examples of new proteins like nylonase, or by claiming that the normal definition of "information" does not apply to the genetic code.  Both of these claims are still being disputed.

It is surprising how semantic these arguments can get.  I caution my readers to always define their terms, like "evolution," "species," "kind," "science," and even "creationism," when discussing this subject, because every person has different takes on these words.  Language is a powerful tool, but it is very easy to misuse.  If the person you are talking to does not get the same ideas from your words as the ideas you are trying to convey, all sorts of misinformation will be spread, and misinformation is one of the great evils of this world, regardless of your stance in this debate.

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