Friday, March 28, 2008

Micro vs. Macro Evolution

I suspect some of my readership may be getting bored with all this evolution vs. ID stuff so I promise after this post we will return to our regular scheduled programming!

A favorite ploy of creationism is to accept microevolution (e.g. Darwin's Finches) while rejecting macroevolution (new species, birds descending from some dinosaurs, etc.) There is plenty of credible discussion about micro and macro evolution on the web so I am not going to repeat it here. See Douglas Theobald , John Wilkins and Wikipedia. I'd like to instead address the kinds of drivel exemplified by the thousands of posts like this one. Here we see an author asking "When Did the Fish Sprout Legs?" and then denying such a leap is physically or biologically possible. Here is an excerpt:

When one examines the historical record of life, we find the absence of transitional forms between the major life groups such as fish and amphibians or reptiles and birds. The fossil record has failed to yield the host of transitional forms demanded by the theory of macro-evolution. Rather, the fossils show an abrupt appearance of very distinct groups of animals. Take, for
example, the supposed"fish-to-amphibian" transition. The general assumption has
been that the earliest amphibians evolved from the order of fish, the Rhipidistia. However, there are major differences between the earliest assumed amphibians, the Ichtyostega, and its presumed fish ancestor. The differences are not simply a few small bone changes but are enormous structural differences as can be seen in Figure 1.The first amphibian had well-developed fore- and hind limbs which were fully capable of supporting terrestrial motion. The transitions between the two are strictly hypothetical, and no transitional fossils have ever
been found ... only imagined and artistically drawn. The mechanism for the
supposed macro-evolution of the fish to the amphibian is purely hypothetical.

When I was a boy my family used to picnic at Westbury Gardens in Long Island. There is a large pond there where I used to love to catch frogs to take home. There was also a shallow area where there were steps leading into part of the pond. Around these steps swam hundreds of tadpoles. One day I decided it would be really cool to capture some tadpoles and take them home to watch the transition of a tadpole into a frog. So I caught about a dozen tadpoles and took them home and placed them in a fish tank. I waited and waited but they never turned into frogs. Clearly I did not provide them with the right environment and nutrients to allow this transition to occur.

Can we learn anything at all from my boyhood escapade? Well clearly I am not going to claim that the transition from tadpole to frog is an example of macroevolution at work. Clearly the transition is preprogrammed and does not involve any mutation or selection. But here is what is interesting and very instructive:
  1. A tadpole looks far more like a fish than it does a frog.
  2. Everyone knows that tadpoles do sprout legs and become frogs given the correct conditions.
  3. We also know that the transition from tadpole to frog is not instantaneous and each intermediate form is viable.
  4. We learn from my experiment that given the wrong environment a tadpole will remain a tadpole and eventually die.

So in a time frame far far shorter than any timescales on which macroevolution occurs we see a fish-like-thing turn into a frog. Fascinating really. What is fascinating is not that this is a proof of macroevolution. It is not. What is fascinating is that it is there is a stable trajectory through genotype space that leads to a stable trajectory through phenotype space that manifests itself as a fish transforming into a frog. The mechanisms by which genes switch on and off in the case of tadpoles are based in regulator genes, enzymes, etc. and not mutation and selection. But so what?

If you accept micro-evolution, whereby selection and mutation lead to small changes in form and you witness for yourself a purely biological process whereby a rather large morphological change can occur in a span of weeks, how can you not at least admit to the possibility of macroevolution? Oh right, it’s not in the bible. Sorry, I forgot.

p.s. I just found similar ideas by someone much more qualified than myself. Definitly worth a read.


Jason said...

I believe in microevolution, but not macroevolution.

I also believe in islands, but not continents....

Excellent post! I've never read your blog before, but I never get tired of this topic!

Sal Mangano said...

Thanks Jason. I just added your site to my blog roll because the Earth Noobs post made me laugh.

Jason said...

Thanks Sal! I wasn't sure that joke would work.

Bunc said...

Hi there,
Just stumbled on you. Dont apologise for taking creationists to task. Its probably the biggest fight to protect rational thought that there is at the moment.
Sadly despite their lack of any intellectual merit or rigour their arguments do influence some people. It's important that we all keep challenging their nonsense at every opportunity.

Sal Mangano said...

Thanks bunc, but I was not really apologizing for taking on the creationists. I was getting a bit bored with it and thought that some others might be as well.

See, you can't really "take on" a creationist. I have as much chance of convinicing a creationist of the errors in their thinking as they have in convincing me. So after a while debate just degenerates into an ego thing. This is why a cut off the debate with Credo in another post.

The reason I post is for the benefit of those folks who may be on the fence. Especially kids in middle or high school that might be easily taken in by the sheer magnitude of bunk out there. It seems for every blog or web site that presents a scientific view of origins there are ten sites offering various degrees of misinformation.

It unfortunate that the majority of intelligent folks don't buy into ID one bit but it’s the kooks who have so much time on their hands to spread half-truths, cherry picked quotations and outright lies.