|Turned up to eleven: Fair and Balanced|
Wednesday, May 29, 2002
I am probably going to regret this, but I think that the topic of Evolution is worth my time. Before going into the heavy lifting of the science, however, I encourage my readers to think a bit about their position on Evolution, and where it comes from. If it comes from the Bible, it is not going to be getting much sympathy from me. If it comes from study in the biological sciences, fine. Many people have tried to define the role of science and religion in our lives, and I tend toward the "separate realms" notion, that Religion has nothing to say about the validity of a given scientific result, and Science has nothing to say about religious notions. They intersect, mainly, where people perceive that Science is attempting to disprove religion. As I have said here before, I am an atheist, that is I explicitly deny the existence of God. If that offends you, then this is probably not the right blog for you. If you want to argue with me about that, I am ok with that, but I will not be explaining myself over and over, so I may just refer you to past comments/writings. With all that said, here goes nothing!
A note on terminology/PR I have noticed an interesting phenomenon among opponents of Evolution (think about that; how many opponents of Gravity do you know?); they call scientists who argue with them "evolutionists". Presumably (careful with those! -ed) this is to draw a contrast with "Creationist", or perhaps a parallel with "Marxist" (see No Watermelons for additional info on hidden Marxists!), "leftist", etc. I always think this is funny. Am I a "gravitationist" if I observe that every time I throw something in the air, it comes back down? Am I a "particle physicist" if I observe the energies of freed subatomic particles after smashing atoms together in a cyclotron? (Just kidding about that last one; I would be a particle physicist if I did that)
Let me set out my "humble" opinion on this issue at the outset; Evolution happens. The evidence is overwhelming. The fossil record shows that life has existed on this planet for ~3.5-4 billion years, and in that time has evolved from single celled organisms alone (probably with RNA as their genetic material), to the incredibly diverse biota of the current earth. Natural selection has been observed in all sorts of species, including but certainly not limited to bacteria and insects. Unnatural selection (that is, breeding of domesticated organisms) has resulted in the pets that we routinely give our children. Genetics has shown us unequivocally that there are genes present in human beings that are also present in bacteria, and that genes responsible for very different activities are related to one another by sequence. The pieces of evidence for all of this are myriad and deeply convincing, provided a basic understanding of molecular biology (no small thing, I know!). I have been involved in several long conversations on this issue at No Watermelons and Transterrestrial Musings, and the problem can be succinctly described thusly; Either people come into the argument convinced that Evolution must be wrong because it "denies the existence of God" (it doesn't), or they get bogged down in semantics (what defines a species, for example), and lose sight of the major issue at hand.
Here is the point that I would really like to get across to any reader. Life is Beautiful, Wonderful, Fascinating, and Rich. There are so many absolutely astounding things going on in virtually every creature that lives on this planet, a person can spend an entire lifetime studying one small facet of the life of a tiny microbe, and still be surprised at what they find. Amazingly, however, when you look at all of this wonderful life, you find that there are many things that we all do the same way. For example, virtually every organism on the planet uses Adenosine triphosphate (ATP) as an energy storage molecule, retrieving stored energy by breaking a phosphate bond (ATP to ADP). This is a great energy storage reaction, because the bond has a peculiarly high level of energy, but it is hardly the only possible way. Likewise, virtually every organism uses the "proton motive force" as a mechanism for deriving the energy stored in this molecule. Basically, microbes (and higher organisms, in their mitochondria) set up a gradient of protons across a membrane, so there are more protons on the outside than inside, and then, as the protons flow in, they are coupled to a chain of oxidation-reduction reactions. The net result of all of this is the formation of ATP molecules, using a mechanism called "the TCA cycle", or the "Krebs cycle". I don't want people to get bogged down in the biology of these things, just to recognize that almost every organism uses these systems, in one form or another. Another example is photosynthesis. A substantial number of very different organisms capture sunlight and produce energy, releasing molecular oxygen as a result. But there are only two ways to do photosynthesis (Photosystem I and II).
When you get into more detail in any given system, you find evidence of evolution. For example, the lens of our eyes is made of a protein called crystallin, which creates a transparent, flexible matrix that focuses light on the retina. A remarkable development, no? Interestingly, it seems to be related by sequence to proteins in bacteria called "chaperonins" (Here is the abstract for a review). Chaperonins, also called "heat shock proteins", are small proteins that bind to other proteins to prevent them from destruction by the cell while they get shipped from the nucleus (in eukaryotes) or from where they form to where they belong (in the cell membrane, for example). So these small proteins with a totally unrelated job (shipping unfolded proteins around the cell) were co-opted by evolution to make a transparent, flexible lens for focusing light on the retina. This is a deeply interesting result, because it is truly unpredictable. It suggests that the human body, far from being a flawless design, is cobbled together from the materials at hand.
I haven't touched upon the myriad examples of bacterial evolution, but I will simply describe an experiment that every microbiology student does. Microbiologists use petri dishes to grow bacteria, and in that dish we use a gelatin like substance called agar. You melt it, pour it in the plate, and let it harden at room temperature. You can add virtually any soluble substrate or inhibitor, and it diffuses freely, resulting in a uniform growth medium. Suppose we wanted to "evolve" (in the lab), a strain that is resistant to penicillin. If we place our plate at an angle, we can pour a plate with an uneven depth, i.e. on one side it is thick, and on the other side it is thin (image a wedge of cheese). Suppose we put an antibiotic in that agar. We then put the plate flat (after it has solidified), and we pour more liquid agar on it, until the surface is even (image two wedges in opposite orientations, forming a rectangle). We know have a gradient of antibiotic on the plate. If we spread our bacteria on this plate, they will grow up to a certain point on the plate, where the concentration is too high. If we pick cells from that edge, and do it again, the edge will be farther along (closer to the high concentration end) each time. After a few iterations of this, the bacteria will grow everywhere on the plate, being resistant to the antibiotic treatment. If you do this enough times in enough ways, on different traits, you can make the new bacteria very different from the original culture. If you then hand them to someone who has no idea what happened, and you do it right, they won't be able to tell that they were related. Presto! You have just made evolution happen. Of course, nature often takes much longer to do this than we do, but the principle is exactly the same.
Let the deluge begin!