Geneticists Duel Over Dates for “Y-Chromosomal Adam”

Setting the molecular clock to ring for “Adam” is creating controversy among geneticists. Rather than acknowledging the limitations of their craft, genetic clock-makers are resorting to pejorative assessments of each other’s science.

Y-Chromosomal Adam from Cameroon

The story of this “Adam”—Y-chromosomal Adam, not the historical Adam of the Bible—began when the family of a deceased African-American named Albert Perry sent Mr. Perry’s DNA to the National Geographic Genographic Project.

Over time, harmless point mutations in chromosomes produce unique combinations that can be used to trace ancestral relationships and even geographical origins. The Y-chromosome provides the easiest-to-track ancestral clues in men since it is passed on through males without the parental shuffling that happens on other chromosomes.

Mr. Perry’s Y-chromosome didn’t match any of the data on file. The search for his roots led to Camaroon’s tiny Mbo population. This ethnic group genetically has so little in common with the rest of the genetically-mapped world that authors of the latest study of Mr. Perry’s Y-chromosome say its uniqueness “justifies its moniker ‘the Y-chromosomal Adam haplotype.’”

This family tree illustrates the reason Y chromosome and mitochondrial DNA is useful for tracing ancestry. Only males have Y chromosomes. Unmixed with DNA from the mother, these are the easiest-to-track portions of the male genome. Mutation patterns on the Y chromosome can be matched with similar patterns from other men whose DNA is in the database. In this way, people can be grouped according to their shared common ancestors. Similarly, even though everyone has mitochondrial DNA, it is passed on through the mother without much opportunity for alteration, so its mutation patterns can also be traced. The effort to determine how long ago people shared a common ancestor, however, is flawed by many unverifiable assumptions. Image: saypeople.com

Clocking Controversy

Molecular clock dating of Mr. Perry’s Y-chromosome led to a now-controversial paper in the 7 March 2013 issue of the American Journal of Human Genetics. Commenting on his study, Michael Hammer explained, “Our analysis indicates this lineage diverged from previously known Y chromosomes about 338,000 years ago, a time when anatomically modern humans had not yet evolved. This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent.”

This “is hugely larger than all the other or subsequent estimates”1 of the age of modern humans. A competing analysis of Mr. Perry’s Y-chromosome, without disputing Mr. Perry’s descent from an ethnic group that diverged from the rest of humanity early, draws less dramatic conclusions about when that happened.

“We can say with some certainty that modern humans emerged in Africa a little over 200,000 years ago [208,300 =/- 5%, to be precise],” says Eran Elhaik, lead author of the new study in the European Journal of Human Genetics. “We have shown that the University of Arizona study [led by Hammer] lacks any scientific merit. In fact, their hypothesis creates a sort of ‘space-time paradox’ whereby the most ancient individual belonging to the Homo sapiens species has not yet been born.”

Besides producing an estimate older than the age commonly assigned to anatomically modern humans, the dates from Hammer’s lab “significantly predated the most ancient mitochondrial DNA,”2 which had recently been happily reconciled. (You can read about this reconciliation of Y-chromosome Adam with Mitochondrial Eve in “Circular Reasoning Surrounds Human Origins, but Even a Broken Clock Is Right Twice a Day.”) Elhaik compares the mismatch created by Hammer’s conclusions to the popular time-travel dilemma suggested in the film Back to the Future. Recalling how the character Marty fears if his parents do not meet he will never be born, Elhaik says, “It’s the same idea.”

The Criticisms

“Such an extraordinarily early estimate contradicts all previous estimates in the literature,” Elhaik and colleagues write, and are “142,000 years older than the oldest known anatomically modern humans.”3

Elhaik’s critique of Hammer’s analysis hinges on the assumptions he made, the data he ignored, the portion of the Y-chromosome he examined, and the parameters he used in his statistical analysis. Elhaik writes that all these “methodological irregularities and analytical biases”4 pushed the results deeper back into time. He casts more than a hint of shadowy suspicion on the quality of the science coming out of Hammer’s lab and the integrity of those involved. Elhaik writes, “We have shown that consistently throughout their examination, Mendez et al. [coauthors of Hammer’s study] have chosen the assumptions, approximations, numerical miscalculations and data manipulation that inflated the final TMRCA [time to the most recent common ancestor] estimate.”5

Hammer answers, “The paper by Elhaik and colleagues . . . does not present a convincing argument against our paper and unfortunately at times appears to display a lack of technical understanding of the subject area. We are in the process of submitting a rebuttal.”

Poor Assumptions by One and All

Molecular clocks—like all clocks—must be powered by a mechanism that consistently ticks off time at a known rate. For molecular clocks, this is the mutation rate. Mutation rates are difficult to know, even in the present when extrapolated from the DNA of representative members of a population. It is impossible therefore to know what mutation rates were once upon a deep time. (We of course, contend that both humans and the earth are only 6,000 years old, making any mutation rate giving an age of 200,000 years ago to be significantly outside the realm of reality.)

It is impossible to know what mutation rates were once upon a deep time.

The mutation rate paces the molecular clock. Mutation rates vary for each chromosome, Elhaik points out, and are especially variable for Y-chromosomes. Yet Hammer’s lab used mutation rates for autosomal (non-Y) chromosomes in its Y-chromosome-based clock.

The Y-chromosome substitution rate that Elhaik prefers was obtained from two Europeans separated by 13 generations. Elhaik accepts this rate as the preferred standard, not just because it was obtained from Y-chromosomes, but because it is “consistent with estimates derived from human-chimpanzee Y chromosome analyses.”6 In other words, the number Elhaik favors is acceptable to him because it fits the evolutionary times calculated on the basis of belief that chimp and human evolutionary lines diverged from a common ancestor millions of years ago.

Elhaik further criticized Hammer’s choice of generation length—a number that dramatically affects results. The time for each generation determines how fast the genetic clock ticks. The age at which men and male animals reproduce also affects the number of substitutions in the Y-chromosome because older males have accumulated more genetic changes in their germ cells. Elhaik disapproved of Hammer’s use of 30 years as the average age at which a man would reproduce and recommended an age younger than 20.7

Without historical records, scientists cannot know the generation time of ancient people, yet without the generation time, molecular clocks cannot be calibrated. While we don’t know the generation time for all people in all times and places, as Ken Ham recently pointed out, “There is a book . . .” germane to the issue. In the Bible we have generation times for many ancient people. Generation times have varied a lot, we learn, and people used to live much longer than they do today. From those carefully preserved, internally consistent genealogies, we can trace certain family lines from Adam to the time of the Babylonian destruction of Jerusalem—a date known to secular history. From this we calculate how long ago God created the real Adam, the father of all people who ever lived. God created the earth and Adam about 6,000 years ago. And unlike the metaphorical Y-chromosome Adam and Mitochondrial Eve, the real Adam and Eve had no trouble meeting, for God created them the same day.

Elhaik also criticized the Y-chromosome segment Hammer’s group assessed as too small. He writes, “a reliable evolutionary estimate cannot be obtained from 2% of the male-specific portion of the Y chromosome.”8 Furthermore, he notes “the authors chose to omit 60000 bases of it because they consist of ‘a large amount of mutations.’”9 Certainly these mutations would have altered the rate at which this clock ticked.

Finally, Elhaik critiques the statistical judgment call made by Hammer. By opting to do the calculations the way he did, the results were dramatically different from those obtained using the statistical parameters Elhaik chose. When we realize that the decision to do the statistical calculations one way or the other is not a matter of being right or wrong but a matter of judgment, the enormity of the error routinely introduced into molecular clock estimates even in the math is apparent.

While Elhaik calls attention to some assumptions used to make time estimates—such as the judgment calls and technological limitations involved in choosing what parts of chromosomes to analyze—he fails to acknowledge the assumptions inherent in all such molecular clock dating schemes.

Circular Clocks

Molecular clock dates bestow the illusion of accuracy upon evolutionary stories, but most people do not realize that molecular clocks are monuments to circular reasoning, statistical fallacies, and evolutionary assumptions. They operate on the basis of unverifiable assumptions powered by other assumptions and confirmed by still other assumptions.

Molecular clock predictions are built upon a statistical house of cards, attempting to predict how long evolution would take if it could happen and if stable mutation rates were known. Human molecular clocks, in particular, rely on the assumption that chimps and humans share a common ape-like ancestor. The expected time for differences to diverge from this hypothetical ape-like ancestor to produce modern human and chimp DNA is used to calibrate data. An additional layer of assumptions is introduced to this mélange when dates derived from radiometric dating methods are applied to pinpoint watershed moments in evolutionary history supposedly documented in the fossil record

Elhaik points out where Hammer’s assumptions and judgments skewed his conclusions. However, if Hammer’s conclusions had not rocked the evolutionary boat, likely no one in the evolutionary community would have questioned his assumptions. While Elhaik is critical of Hammer’s assumptions, many other assumptions foundational to genetically clocking deep time are just as questionable.

Both Hammer and Elhaik’s work is based on the assumption that molecules-to-man evolution really happened. The statistical analysis then used to assign dates to the days of our evolutionary past, whatever its additional assumptions and limitations, takes place within the house of cards on which the evolutionary clock is calibrated.

Which Adam And Eve?

Of course, Y-chromosome Adam and Mitochondrial Eve have nothing to do with our first parents identified in the Bible. These terms relate to individuals within a small population group from which all others diverged. Some evolutionists are unhappy about the popular borrowing of the biblical couple’s names, fearing such metaphorical use somehow lends credence to the biblical account. As Bible-believers, we do not look for either the age of humanity or proof that Adam and Eve were historical people in evolutionary genetics. Such molecular clock dates are rooted in the evolutionary bias of fallible people.

The genetic sequence found in “Mitochondrial Eve” can, however, offer some clues about the biblical Eve. A recent study of mitochondrial DNA worldwide revealed “an unexpected lack of diversity” which is most consistent with the biblical account and quite inconsistent with evolutionary versions of human history. The creation scientists who authored the study wrote, “Given the high mutation rate within mitochondria and the large geographic separation among the individuals within our dataset, we did not expect to find the original human mitochondrial sequence to be so well preserved within modern populations. With the exception of a very few ambiguous nucleotides, the consensus sequence clearly represents Eve’s mitochondrial DNA sequence.” Read more about the insights that genetics can offer about the woman that Adam—about 6,000 years ago—called “the mother of all living” in “The ‘Eve’ Mitochondrial Consensus Sequence.”

Biblical history, preserved through our all-knowing Creator God, is not at odds with the real observations of science. From that history we obtain real information by which we can know the age of humanity. We learn that all of us are descended from just two people created in the image of God about 6,000 years ago. We also learn that the death and suffering in the world today began with their rebellion against their Creator. Understanding this truth, we see God is not only just but also loving, for Jesus Christ the Son of God came into this world as a man—the “Last Adam” (1 Corinthians 15:45)—to suffer death on the cross, making redemption and salvation available for the descendants of the first Adam. The Bible reveals humanity’s true heritage as well as how we may through God’s grace inherit eternal life (1 Peter 1:3–5).