Saturday, 20 June 2009

• Currently Icons of Evolution: Science or Myth? Why Much of What We Teach About Evolution is Wrong By Jonathan Wells see related

  Why Microevolution Obligates Macroevolution

  Back when I was a new Christian and the people who were teaching me about it included anti-evolutionism as part of it, much was made about the difference between microevolution and macroevolution. I was told that microevolution, genetic change within a species, is perfectly acceptable, and humanity’s success in selective breeding is a good example of it. Macroevolution, though, the arising of a new species from a previously existing one, was the line drawn in the sand that no one opposed to evolution could budge on. In this post I’m going to explain how I came to realize that to accept microevolution while rejecting macroevolution is to fool oneself. There is no fundamental difference at all between the two.
  

  
  

  
  

  The above illustration is a common creationist depiction of micro vs. macroevolution, taken from a "creation science" website showing how "changes are lizards are still lizards, and will never produce a bird." We're going to ignore archeopteryx for the sake of this cartoon, and the fact that nobody believes a current-day lizard turned into a roadrunner.
  

  I’m going to define a species as a population or organisms that can successfully breed with any other member of the population and produce fertile offspring. Now it’s true that biologists continue to argue about the nuances of defining species, but the definition I’m using is broad enough to be acceptable to everyone involved in that controversy. This also holds for typically asexual creatures, because they almost all have the ability to reproduce sexually when they choose to and this suffices for our definition. Asexual reproduction makes more offspring for a given amount of resources, but sexual reproduction makes more robust offspring, which is why creatures able to reproduce both ways will reproduce sexually only when under stress.

  We’re going to start with the assumption that microevolution occurs. This means that the gene pool of a species can change over time. What we need to show is that this change over time is enough for a new species to arise. Here then is what we will do: we will put a representative sample of the species into suspended animation while the rest of the population experiences microevolution through the normal processes of genetic drift and mutations. We’ll thaw out our sample of the original species periodically and let it try to breed with the sample that has been changing. Clearly the genetic differences between the frozen and microevolving populations can only increase with time. The question of course is, given enough time will there ever be so much difference that the two populations cannot breed?

  I think the burden of proof is on the skeptic to show that no matter how much microevolution occurs, it will never introduce enough genetic differences to create a new species. Consider red-tailed hawks. Not only do they come in a dark phase and a light phase, they also range from coast to coast. Hawks of different phases can breed together, as can hawks from different areas of the country. It is unlikely that Georgia hawks and Montana hawks breed often, though, and each phase prefers mates of its own phase, so you have several sub-populations within the red-tailed hawk species that typically only breed amongst themselves. Microevolution will tend to increase the differences between these sub-populations, at a rate roughly proportional to the frequency that matings occur between them, yet all these sub-populations remain a single species, except in the case of my favorite example, the ring species. Do this process many times on many different species and it will become apparent that there is an amount of genetic variation that can be tolerated within a population while still permitting successful breeding—but at the same time there is also an amount that is too much. In the case of humans and chimpanzees, for instance, 1% is apparently too much difference.

  The skeptic must produce a mechanism that allows microevolution to introduce genetic change but prevents it from introducing too much change. Irreducible complexity is not such a mechanism, by the way. Instead it is merely an observation that suggests that mere natural selection cannot be the mechanism that does produce macroevolution. IC can do nothing to prevent macroevolution, nor does it claim to. What it has done, however, is prompt more rigorous research into an area where evolutionary biologists had perhaps been lazy, and this research has refuted IC (IC was a fragile idea anyway since by making a universal claim about the futility of natural selection it was only necessary to demonstrate that natural selection could in one instance produce an irreducibly complex structure, and we needn’t know how all the rest of the irreducibly complex structures formed, IC has already fallen with the one counterexample).

  One reason I don’t think such a mechanism exists is that there is no reason to expect it, since it is fairly straightforward to conclude from the physical evidence that macroevolution has indeed occurred. The fossil record show a tree of similarities in body plan; genetic mapping, for instance of cytochrome C, shows a tree of similarities that has nothing to do with body plan but is nevertheless so much like the one derived from the fossil record as to leave no doubt that they are recording the same history of common descent. If we already have microevolution, and we have a history of common descent duplicated in disparate sources, then why shouldn’t we conclude that microevolution produces macroevolution??? Yet some people are so predisposed against macroevolution that they simply cannot accept it when it slaps them in the face. They invoke an Intelligent Designer to produce every episode of apparent common descent, as if He is an assembly line worker in the species factory and day after day he makes from scratch brand new species that happen to look just a little bit different from the species he made from scratch yesterday, right down to their DNA. A truly intelligent Designer would design a universe that didn’t have a mechanism in it preventing macroevolution, let microevolution do the dirty work naturally, and go fishing or something.

  But wait! Big deal, the skeptic says, since it is not possible to pluck a sample of what a population used to be out of the past, your experiment doesn’t really result in speciation. Any member of the population can always breed with every other member of the population alive at the same time, so it is always the same species. All that is happening is microevolution and I’ve always said I don’t have a problem with that!

  All right, I’ll concede that objection. Let’s do this instead. Instead of putting the control sample in suspended animation, let’s split the species into two halves and put some barrier between the halves that we don’t let them cross. Now there is no control group. Population A is going to undergo this genetic drift you’re talking about, and so will Population B, and it is impossible that they will both undergo the exact same changes at the exact same time. From time to time we’ll take representative samples of A and B and reunite them in a zoo and see if we get any offspring (for we have to keep A and B separate or the experiment is ruined). Remember, we’ve established that given enough time neither A nor B will be able to breed with the start population, and all that is required is to show that the difference between changing A and changing B is as much as the difference between changing A (or B) and the original population. If A is different from the start population, and B is different than the start population, then there is a roughly 50/50 chance that they’ll be even more different from each other.  If they are less different to each other than either is to the start population (as if they both walked generally east from the start point instead of one east and the other west) then just wait a little longer. Every population split into two separated halves will accumulate genetic differences between the halves at some rate, because the changes that occur in one half are not shared with the other half, which is known as allopatric speciation. Inevitably the genetic differences will be so great that the populations, if somehow reunited, would not be able to breed. A and B are now two separate species, no magic deep freezer needed!

  
  

  Well, populations splitting like that don’t happen very often, the skeptic might complain, but he’d be wrong. There are lots of ways that populations are split apart. Usually populations are physically separated, for instance by a river drying up between two ponds, by a natural disaster that wipes out the species in the middle of its range leaving two isolated ends, or a physical barrier like a river between two ponds drying up. Other times it is a behavioral split: one part of the population will become nocturnal and the other diurnal, for instance. Plate tectonics will suffice as a last resort. There are so many mechanisms by which populations can be split into two or more smaller groups that cannot or do not interact with each other that it is impossible to argue that populations breaks never happen. Again, the burden is on the skeptic to show that all species remain eternally monolithic.

  Here it is in a nutshell:

  You can’t have microevolution without macroevolution, because populations break apart. The genetic differences between the two halves can only accumulate via microevolution, resulting inevitably in macroevolution when the genetic difference become too great for the halves to successfully breed together should they be reunited.

  And now you know why if you are opposed to macroevolution you are forced to be a young-earther: the only way to prevent this process, the only way to have your micro- without your macro-, is for there not to have been enough time.
  

   

  P.S. Would anyone be interested in my review of Jonathan Wells' Icons of Evolution, either in video form (which 5/6 of is available online) or in book form (I would slowly debunk a shorter pamphlet he distributes for free, but I'm almost done with the entire book at the moment)? And if so, would you prefer a review of the book/pamphlet or of the video?
  

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