Maddenation
The evolution of evolution
A recent NOVA episode on “what Darwin never knew” was one of the best I’ve ever seen. It celebrated the 200th birthday of Darwin and the 150th anniversary of his epic publication on the origin of species.
What I remember most from this fascinating documentary is my feeling of incredible awe at the mind-boggling complexity and yet simplicity of life. We all now know about DNA and genes and the natural selection that acted on the billions of variations in life forms to shape all the species we know of today. What amazes me, and lots of scientists, is that it takes relatively few instructions (genes) to account for all that variation. Humans have only 23,000 genes, about the same as chickens, but less than corn and some worms. What is more, some of the differences between the human genome and lesser animals seem more like defects than well-planned instructions.
One amazing example is a gene that differentiates humans from apes and other animals. This gene directs the construction of jaw muscles. The “defects” in the human gene make our jaw muscle much weaker than similar muscles in apes. However, because this muscle is anchored in the skull, it impacts cranial growth. To house and support the strong ape muscle, ape heads freeze at about the age of three and are therefore smaller. Humans, with a weaker muscle, have heads that continue to grow up until about age 30, leaving more room for the brain, which is twice as large as ape brains. Other genes direct human brains to grow for a longer time and reach larger size and complexity than ape brains, but these genes too look more like odd mutations than carefully crafted instructions. Amazing.
The same genes grow arms and legs and fish fins for all animals. It’s just that DNA elements called “switches” turn these genes on and off at different times. Thus the “book of life” is remarkably similar for all of life on earth. Written in a language containing only four “letters” (alleles) the book for humans is only 23,000 “words” long. Heck, a 50-page book contains more words than that! True, there’s lots of other strange genetic material in the 3-billion letter long DNA molecule (that’s like 1000 big books), but we’ve yet to figure that out. Lot’s to wonder about.
Dad • Ideas • 01/08/10 • 0 comments
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