21 December 2005

Thinking About Evolution

Given that the whole Evolution vs. Intelligent Design debate has been in the news so much recently, I did some thinking on the matter. At the beginning of the process, I found Evolution to be a little ridiculous. There are some pretty glaring problems: the one that bothers me most is that pesky Second Law of Thermodynamics: If things tend to become less and less organized over time, how on earth is Evolution going to somehow continually produce newer, better adapted species over time - by accident. I'll be the first to admit that I am at best a hobby physicist - all that math intimidated me, or I might have grown up into an astrophysicist rather than a piano teacher. Still, I enjoy reading Stephen Hawking's books and discussing experimental vehicles and power sources with my husband. Maybe somewhere some enterprising disciple of Evolution has taken on the Second Law and I just missed it. But I've never heard of that sort of work being done. At least not yet.

Thing is, I like to keep an open mind. As my own high school education lacked any kind of emphasis on Evolution, I went out and found a nice Evolution primer from a reputable source with a name that I recognize - in this case Berkeley and I did my best to set aside my skepticism while I read it.
Berkeley.edu: Evolution 101


Here's some of what I learned:

1. Evolution is a hypothesis. Even Berkeley doesn't tout Evolution as FACT. It's a work in progress.

2. Evolution - both macroevolution (the evolution of new species over long periods of time) and microevolution (changes within a species over one or more generations) happen by way of a couple of very basic processes: mutation, genetic drift, and natural selection. Microevolution, according to the Berkeley site, can lead to macroevolution.

Now for the Thinking Part:

Mutation
Evolution 101 has a glossary, which defines mutation as "a change in a DNA sequence, usually occurring because of errors in replication or repair." It goes on to say, "Mutation is the ultimate source of genetic variation." So, these mutations, these mistakes, are a positive thing. Interesting. I've also been reading Miscarriage: why it happens and how best to reduce your risks by Henry M. Lerner, M.D., OB/GYN. Chapter 2 is about chromosomal causes of miscarriages. Dr. Lerner writes that chromosomal miscombination is the number one cause of miscarriage, and talks about a couple different types. Abnormalities of chromosome number, abnormal chromosome splitting/nondysjunction, and translocations are discussed. Each of these things would be mutations, according to the Berkeley definition. Abnormal chromosomal numbers cause a number of problems, for instance that sperm with too much or too little chromosomes usually can't even fertilize an egg. Nondysjunction is when chromosomes split or pair up incorrectly, and it also leads to cells having the wrong number of chromosomes. Dr. Lerner writes:

"This situation will lead to the abnormal development of the embryo's structural or physiologic features. Usually, such an embryo will die and the pregnancy will miscarry. The most common example of aneuploidy see in living infants is Down syndrome, where each cell in the baby has three copies of chromosome 21.

...Trisomy - the presence of three copies of any of the chromosomes is the most frequent cause of first-trimester miscarriages. ... The chromosomes most often involved in these trisomies are chromosome 16, chromosome 21 (causing Down Syndrome), and chromosome 22. Why these chromosomes triple up more often than others is not known. It may be because other chromosomal trisomies are so lethal that they leave egg and sperm incapable of fertilizing one another - thus embryos with these chromosomal structures rarely form. alternatively, it may be that when other triosomies occur they result in miscarriages at such an early stage that not enough pregnancy material is recovered for their chromosomal makeup to be identified." (page 38)

The outlook an embryo with translocations in its chromosomes is equally grim. A lucky few will have "balanced" chromosomal translocations. These will probably survive into adulthood, but suffer from higher rates of infertility, miscarriage, and "fetuses with congenital anomalies". Not exactly good for introducing "positive" mutations into the species. And that's the best case scenario.

Dr. Lerner concludes his section on chromosomal abnormalities with these words:
This then is why abnormal chromosomal structures lead to miscarriages: Not only will abnormal chromosomes "miscode" for the development of the building blocks of all tissue, the proteins, but they will likely produce incorrect messenger signals as well. Either sort of biologic mistake - incorrect proteins or incorrect physiologic signaling - can be fatal to a developing embryo.

Genetic Drift
The Berkeley site comes right out and says that Genetic Drift is pure chance, and that it does not produce adaptations. Change, yes, but completely random change. Some organisms will leave more descendents than others, making their genes more common. So you might end up with a generation of people with big noses, if a large number of small-nosed parents are killed in accidents. Not exactly ground breaking "evolution." I'm really not sure how fluctuations in the frequency of any given trait in a population relates to evolution, even after reading Evolution 101, unless for some reason a trait goes extinct.

Natural Selection
Natural Selection is where I see the conflict with the Second Law of Thermodynamics. The idea is that there are different traits. The example used by Berkeley was green and brown beetles. So, if the predators can find the green ones, but the brown ones are better hidden, then there will be more brown babies, because the green ones are eaten for lunch. As this happens, there are more and more brown beetles, until you just don't find any more green ones. At the end of the "selection" there are fewer varieties of beetle than there were at the beginning. But somehow, over time, the pattern is supposed to create more variety? The example that Berkeley shows follows the Second Law - there is less variation at the end. But the principle that they were trying to teach doesn't seem to follow either the example or the law.


So, at the end of the day, I find that I am still unconvinced by Evolution, in spite of the fact that Berkeley's Evolution 101 was very well done and very interesting. And given that Evolution is a hypothesis, I don't understand the fuss about having a competing hypothesis or two.


Further Reading:
Berkeley.edu: Evolution 101
The Society for the Study of Evolution
Interactive Documenary: Becoming Human
PBS: Evolution
NY Times: The Evolution Debate
Institue for Creation Research
Mormanity's Blog: Dec. 19 - Would we fly to pieces?

2 comments:

Slain said...

Very well thought-out piece.

Recently a segment in Discovery mentioned that dinosaurs died out only 300,000 years after the cataclysmic asteroid hit the earth..

Tianna said...

Finally got around to reading this post. The points you have regarding macro evolution point out what seems to be apparent flaws in the hypothesis. I wonder why this particular hypothesis has persisted for so many years? It doesn't quite make sense to me.

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