Dr. David Plaisted is a professor of computer science at the University of North Carolina, Chapel Hill. He has written numerous papers dealing with mathematics and computer science. He is very interested in creation science and has a web site containing 50-60 articles, which includes "A Dummy’s Guide to Genbank": www.cs.unc.edu/~plaisted/ce/index.html

New evidences suggest that the human race is very young. The journal Science recently reported that the age of the human race is roughly 1,000 to 10,000 generations. Other information about mitochondrial DNA mutation rates gives an even younger age than 1,000 generations.

Age estimates are obtained by observing differences between the DNA of different individuals, and calculating time of divergence using estimates of mutation rates. Mitochondrial DNA is often used since it is separate from the bulk of DNA found in the cell nucleus. Mitochondrial DNA has about 16,000 base pairs and mutates, apparently, much faster than nuclear DNA. Human mitochondrial DNA has been completely mapped, so all the coding regions are known, as well as the proteins or RNA for which they code. Some areas of mitochondrial DNA known as ‘control regions’ do not code for anything. A control region is a non-coding section that seems to have some kind of regulatory function. Because variation among humans is greatest here, scientists think this region mutates faster than any other region.

Recently, mitochondrial DNA mutation rates in the control region were measured directly by comparing mitochondrial DNA from siblings and from parents and their offspring. Mitochondrial DNA was found to mutate about 20 times faster than previously thought, at an approximate rate of one mutation (substitution) every 33 generations. The control region studied has about 610 base pairs. Humans typically differ from one another there by about 18 mutations. By simple mathematics, it follows that the human race is about 300 generations old. If one assumes a typical generation of about 20 years, this gives an age of about 6000 years.

This calculation is done as follows: Assuming all human beings initially have identical mitochondrial DNA, consider two randomly chosen human beings. After 33 generations, two such random humans will probably differ by two mutations, since there will be two separate lines of inheritance and statistically one mutation along each line. After 66 generations, two randomly chosen humans will differ by about four mutations. After 100 generations, they will differ by about six mutations. After 300 generations, they will differ by about 18 mutations, the observed value.

The mathematics is extremely simple. However, this timetable would revolutionize the history of humanity from a scientific standpoint, so biologists attempt to explain away the data. They do this by assuming that most mutations in the control region are harmful. This means that many mutations would be fatal. Among surviving individuals, therefore, the number of mutations would appear to increase more slowly.

This explanation is implausible for several reasons. First, we know that the control region does not code for any protein or RNA, so it is unlikely that mutations there would be harmful. Second, large variation in this region might imply that mutations there do not have a harmful effect. Finally, one study noted that humans evolve (that is, accumulate mutations) 1.8 times faster in the control region than in silent sites in the mitochondrial DNA. Silent sites do not affect the amino acid coded for, so they generally do not have much effect. [A silent site is any one of two or more DNA codons for the same amino acid.] A codon consists of three nucleotides and it codes for one amino acid. The first and second nucleotides cannot mutate without changing the amino acid for which they code. The third nucleotide of the codon (or triplet) can mutate and still code for the same amino acid as the original triplet. This is known as redundancy. If the mutated codon still codes for the same amino acid, the mutation is not expressed—it is silent. No codon codes for more than one amino acid, showing that the genetic code is specific.

The fact that the control region evolves 1.8 times faster (that is, mutations accumulate 1.8 times faster) indicates that the control region has even less influence than the silent sites, also suggesting that mutations in the control region are not harmful. Researchers found a similar situation in ducks, where the control region mutates 4.4 times faster than mitochondrial DNA in general. In summary, evidence suggests that the control region is not constrained much and mutations there are not very harmful.

The most reasonable interpretation of the data, then, is that the human race is in fact about 6000 years old. It is possible that the mutation rate has changed to some extent throughout history, but it is hard to imagine this making much difference in the end result. Since mitochondria in all organisms are quite similar today, it is reasonable to infer that they were also similar in the past and had a similar mutation rate.

An environmental agent (mutagen) would probably cause a constant increase in the number of mutations per unit time, roughly the same for nuclear and mitochondrial DNA. Since mitochondrial DNA mutates so much faster, a mutagen that appreciably increased its mutation rate would also increase the much slower mutation rate of the nuclear DNA and produce error catastrophe. That is, the population would die out due to many harmful mutations.

Another piece of data indicating a young humanity is the striking uniformity of the Y chromosome among human males. This has given an age estimate of about 40,000 years or less for the human race. Since the estimate was made, we have found that mutations accumulate much faster in males than females. The Y chromosome mutates roughly twice as fast because it spends all of its time in males, which mutate more per generation than females. (Non-sex-linked chromosomes would spend half of their time in males and half in females, on the average, and thus mutate about half as fast.) This Y chromosome data might then reduce the estimated age of humanity from 40,000 years to about 20,000 years. (A more recent discussion may be found in Science, which gives older ages.)

Yet another piece of evidence for a young age is the tremendous uniformity found among humans in a 50 kilobase segment of an ALU region of the nuclear DNA. Only one difference was found between humans in this region. More evidences for a youthful humanity are reviewed at www.christiananswers.net/aig/hot/079709.html.

(Before beginning the next section, be aware that molecular biologists do not agree about whether or not the mutation rate is time or generation dependent. Those who favor the molecular clock hypothesis believe mutation rates occur at a constant yearly rate. This group also believes proper use of the molecular clock can date times of divergence, as we reported in our March ’98 issue. Recently, some researchers reported that the molecular clock cannot be determined on the basis of one or two protein/DNA sequences (as we affirmed in our series on the molecular clock hypothesis), and they aver that one can get a reliable clock using 658 genes.)

It will be interesting to see the results of similar studies on other organisms. Probably the only reason that the human race seems so young compared to other species is that it has been studied more. Measurements of mutation rates in other species will probably reveal significantly greater rates than in humans, giving similar young ages if it is true that mutations occur during replication of DNA rather than as a function of time. In fact, there is already some evidence in this direction, also based on mitochondrial DNA. Since mitochondria are similar in all organisms, it is reasonable to assume that mitochondrial DNA mutates at about the same rate in all organisms. Also, all organisms that are roughly the same size as humans should have roughly the same number of cell divisions per generation in the female line. (Males mutate faster because they have so many more cell divisions in the germ line. The number of mutations per cell division is probably about constant). For humans, this is 24 divisions. Therefore, it is reasonable to assume that all organisms whose size is in the range mouse to elephant probably have about the same rate of mitochondrial DNA mutation per generation as humans. One biologist informed me that these assumptions are reasonable.

We have already discussed a portion of the human mitochondrial control region that has about 600 base pairs, and mutates about once every 33 generations, translating to about one percent divergence between two random individuals every 100 generations. Another portion of the control region appears to mutate a little slower, at about one percent every 150 generations. (This follows because typical humans differ by about 8 mutations in a region of about 400 base pairs that was used to study Neanderthal DNA. This amounts to a difference of about two percent.) Therefore, it is also reasonable to suggest that other species in the mouse to elephant range will diverge at about one percent every 100 to 150 generations in the mitochondrial DNA control region.

In this regard, it is interesting to see what the typical differences are between individuals in different species. Wolves and coyotes, for example, differ by about 7.5 percent in the control region. By our previous calculations, it would take about 750 to 1000 generations to achieve this divergence. With a generation time of a few years, this would imply a separation time of a few thousand years ago. Wolves differ from each other by about 2 percent in the control region. This implies an origin about 200-300 generations ago. With a few years generation time, this would be a thousand years or so. This low figure might be explained because the whole control region changes somewhat more slowly than its hypervariable parts discussed earlier. The same reference states that dogs also differ by about 2 percent, leading to a similar time of origin. Most dog species differ within themselves by about one percent, implying a more recent origin.

In a study of seven species of diving ducks, the control region divergence was less than 17 percent. This translates to 1700 - 2500 generations, which at a few years per generation is also in the several thousands of years range. Another study of closely related species of birds found that the difference in total mitochondrial DNA was about 5 percent or less. This probably translates to about 20 percent in the control region, and thus about 2000 to 3000 generations. With 2 or 3 years per generation, this again translates to a separation time of a few thousand years ago.

We can also obtain similar young ages for bacteria and Drosophila (a fruit fly) based on nuclear DNA mutation rates. The generation time for the colon bacterium E. coli is about 20 minutes, or about 50 generations per day and 15,000 generations per year. In 6,000 years there would be about 100 million generations. The mutation rate per base pair per generation is about 10^-9 in bacteria. Thus in 100 million generations, there would be about a 10 percent change in the non-functional DNA and a 20 percent difference between two random individuals. The actual difference observed for E. coli is about 5 percent. This low figure might be explained by a lower mutation rate and by the fact that a considerable portion of the bacterial DNA is functional. We observe mutations in functional DNA less frequently than in non-functional since mutations there are more likely to be harmful and thus the carrier would be eliminated from the population by natural selection.

For Drosophila, the generation time is about 2 weeks. This leads to 25 generations per year, and about 150,000 generations in 6,000 years. The mutation rate for Drosophila is about 2 x 10^-8 mutations per nucleotide per generation or even twice as high or more, according to Kondrashev. This rate may also be computed from the fact that Drosophila has about 20,000 genes, each gene has about 1,000 base pairs, and there appears to be about one slightly harmful mutation per zygote (a fertilized egg) per generation in Drosophila. In 150,000 generations, there would be a change of about 3 x 10³ in non-functional DNA, and about a 0.6 percent difference between two random individuals. Since the mutation rate is likely twice as high, this difference could be as high as 1.2 percent. The observed value is about 1.5 percent. The increase could be due to a slightly higher mutation rate, a slightly smaller generation time, mutational hot-spots, differences at Creation, or an origin slightly longer than 6,000 years ago.

This is just the tip of the iceberg, and many similar results will undoubtedly soon be reported. We hope that these results will cause biologists to give more serious consideration to the possibility that the Biblical record of a recent creation is historically accurate.