by Bill Sardi
Critics of Darwin’s theory of evolution point to flaws in the fossil record (no new species, no missing links) as evidence that the theory is false. But in the 1960s scientists discovered genetic material called DNA and were quick to suggest that the rate of change in DNA is evidence that confirms Darwin’s theory of evolution.
While it is convenient for evolutionary biologists to assume that various DNA proteins evolve at a fixed rate, a recent study blows a hole in this theory. The September 25 issue of the Proceedings of the National Academy of Sciences, geneticist Francisco Rodriguez-Trelles and colleagues at the University of California, Irvine, indicate the idea of a molecular clock may be hopelessly flawed. “It may be ripe for the pawnshop” say Menno Schilthuizen, writing in Science Now.
Calculating the different mutation rates for three well-known genes for 78 species, researchers found widely different mutation rates even for closely related species. “Molecular clocks are much more erratic than previously thought and practically useless to keep accurate evolutionary time,” says Schilthuizen. The authors of the research conclude that the neutral theory of molecular evolution (predictable or constant rates of change) is flawed and that changes in the rate of variation are left to the vagaries of natural selection (randomness). With no evidence to confirm the neutral theory of molecular evolution, scientists say this amounts to a “denial of there being a molecular clock.”
Phosphate – – – – Guanine Cytosine Adenine Thymine – – – – Sugar A DNA Nucleotide Sequence Positions of the middle four proteins differs
DNA is made up of many subunits or strings of sequenced proteins strung between a sugar and a phosphate molecule (called a nucleotide). Think of a wash line in the back yard. There are two poles (the sugar and phosphate molecules) with four proteins (amino acids – guanine, cytosine, adenine, thymine) hanging on the wash line. There are many of these “wash lines” in one gene and over time some of the proteins hanging on the wash line change their positions. One protein may be substituted for another, which is called a mutation. Difference species of life have some of the same genes and therefore the rate of change (number of protein substitutions) can be used to calibrate a DNA clock. Comparative studies of different proteins in various groups of organisms tend to show that the average number of amino-acid substitutions per site per year is typically around 10-9. Calculating backwards, scientists have attempted to use the DNA clock to determine when, let’s say, chimpanzees and man diverged from the same genetic tree. There are a lot of assumptions here (even that there is a genetic tree at all) but the scientists believe humans and chimps split off from a common ancestor about 5.5 million years ago.
But the DNA clock is not so reliable. Paleontologists calculate the Cambrian explosion, the sudden appearance of a fossil record that is rich in almost every species of life, occurred about 540 million years ago. But DNA clock estimations come up with a date of 1 billion years ago for the Cambrian explosion. So there is an unexplainable 500-million year gap. Which provides the most accurate dating, the fossils or the genes?
The so-called neutral theory of evolution holds that DNA mutations (protein substitutions) accumulate at an approximately constant rate as long as the DNA regains its original functions. The differences between the sequences of the same DNA segment (or protein) in two species of life would then be proportional to the time the species diverged from a common ancestor. The undeniable problem is, different DNA protein sequences (or even different parts of the same gene) “evolve” or change at markedly different rates. For example, mutation rates in primates are slower than in rodents. This also assumes that all mutations move progressively rather than in reverse.
If what these researchers say is true, that the theory of a molecular clock is hopelessly flawed, scientists have some real reorganization on their hands. There are no less than 30 textbooks written on molecular evolution in the past decade and numerous PhDs awarded in this area of investigation. To date, no convincing evidence for a phylogeny tree has ever been produced. The evolutionary trees shown in biology textbooks are simply theory, not science. Genetics does not confirm its existence either, though it took scientists more than three decades to determine this. Few scientists are expected to abandon the theory of neutral molecular evolution anytime soon.
- Francisco Rodriguez-Trelles, Rosa Tarrio, Francisco J. Ayala, Proceedings National Academy of Sciences USA, Volume 98, pages 11405-10, September 25, 2001
- Schilthuizen, M, Molecular Clock Not Exactly Swiss, Science Now, Sept. 28, 2001.
- Dictionary of Biology, Oxford University Press, Market House Books, 2000.
- National Human Genome Research Institute
Bill Sardi is a journalist residing in Diamond Bar, California. His new book is Big God vs. Big Science (Here & Now Books, 107 pages, illustrated, $7.00) at www.hereandnowbooks.com.