Reasons to Believe

Conservation Biology Studies Elicit Doubts about the First Human Population Size

Adam named his wife Eve, because she would become the mother of all the living.

–Genesis 3:20

Prior to joining Reasons to Believe in June of 1999, I spent seven years working in research and development for a Fortune 500 company. Part of my responsibilities included method development. My lab worked on developing analytical methods to measure the active ingredients in our products. But more interesting to me was the work we did designing methods to predict consumer responses to our product prototypes.

Before we could deploy either type of method, it was critical for us to ensure that the techniques we developed would generate reliable, accurate data that could be used to make sound business decisions.

Method Validation

Researchers assess the soundness of scientific methods through a process called “method validation.” A key part of this process involves applying the method to “known” samples. If the method produces the expected result, it passes the test. For example, the team in my lab would often develop analytical methods to measure the active ingredients in our products. To validate these methods, we would carefully weigh and add specified amounts of the actives to prepared samples and then use our newly developed method to measure the ingredient levels. If we got the right results, it gave us the confidence to apply the method to real-world samples.

A Controversy about the Size of the First Human Population

Currently, a set of scientific methods resides at the center of an important controversy among conservative and evangelical Christians about the historicity of Adam and Eve. Specifically, the scientific methods in question are designed to measure the population size of the first humans. Even though the traditional reading of the biblical creation accounts indicates humanity began as a primordial pair—an Adam and Eve—all three sets of methods indicate that the initial human population size consisted of several thousand individuals, not two, raising serious questions about the traditional Christian understanding of humanity’s origin. Some evangelical Christians argue that we must accept these findings and reinterpret the biblical creation accounts, regardless of the theological consequences. Others (myself included) question the validity of these methods. It is important to make sure that these techniques perform as intended before abandoning the traditional biblical view of humanity’s beginnings.

The Importance of Adam and Eve’s Historicity

The finding that humanity began as a population, not a pair, causes quite a bit of consternation for me and many other evangelical and conservative Christians. Adam and Eve’s existence and role as humanity’s founding couple are not merely academic concerns. For the Christian faith, the question of Adam and Eve’s historicity is more significant than any business decision that relied on analytical methods my lab developed. (Data from my lab was used to make some decisions that involved millions of dollars.) The historicity of Adam and Eve impacts key doctrines of the Christian faith, such as inerrancy, the image of God, the fall, original sin, marriage, and the atonement.

Again, given the profound implications of abandoning Adam and Eve’s historicity, it is important to know if these population size methods perform as intended. They are a big part of the reason evolutionary biologists and geneticists reject Adam and Eve’s existence. To put it another way, are these methods valid, yielding accurate, reliable results?

Measuring the Initial Human Population Size

Currently, geneticists use three approaches to estimate the size of the initial human population:1

  1. The most prominent method finds its basis in mathematical expressions relating the current genetic variability among humans today to mutation rate and initial population size. Using these relationships, geneticists develop mathematical models that allow them to calculate the initial population size for the first humans after measuring genetic variability of contemporary human population groups (and assuming a constant mutation rate).
  2. A more recently developed approach relies on a phenomenon called linkage disequilibrium to measure the initial population size of the first humans.
  3. The final approach (also relatively new on the scene) makes use of a process called incomplete lineage sorting to estimate humanity’s initial population size. 

Are Population Size Methods Valid?

So are these methods valid? When I have asked evolutionary creationists this question, they usually hem and haw and then reply, saying these methods are based on sound, well-understood phenomena and, therefore, should be considered reliable.

I believe that to be true. The methods do appear to be based on sound principles. But that is not enough—not if we are to draw rigorous scientific conclusions. Scientific methods can only be considered reliable if they have been validated. When I worked in R & D, if I insisted to my bosses that they should accept the results of methods I developed because they were based on sound principles but lacked validation data, I would have been fired.

So given the importance of the historical Adam and Eve, why should we accept anything less for population size measurements?

To my surprise, when I survey the scientific literature, I can’t find any studies that demonstrate successful validation of any of these three population size methods. For me, this is a monumental concern, particularly given the importance of Adam and Eve’s historicity. The fact that these methods haven’t been validated provides justification for Christians to hold the results of these studies at arm’s length.

In fact, when it comes to the first category of methods, I find something even more troubling: studies in conservation biology raise serious questions about the validity of these methods. Of course, we can’t directly validate methods designed to measure the numbers of the first humans because we don’t have access to that initial population. But we can gain insight into the validity of these methods by turning to work in conservation biology. When a species is on the verge of extinction, conservationists often know the numbers of species that remain. And because genetic variability is critical for their recovery and survival, conservation biologists monitor genetic diversity of endangered species. In other words, conservation biologists have the means to validate population size methods that rely on genetic diversity.

In my book Who Was Adam?, I discuss three separate studies (involving mouflon sheep, Przewalski’s horses, and gray whales) in which the initial populations were known. When the researchers measured the genetic diversity generations after the initial populations were established, the genetic diversity was much greater than expected—again, based on the models relating genetic diversity and population size.2 In other words, this method failed validation in each of these cases. If researchers used the genetic variability to estimate original population sizes, the sizes would have measured larger than they actually were.

In Who Was Adam?, I also cite studies that raise doubts about the reliability of linkage disequilibrium methods to accurately measure population sizes.3 Not only is this method not validated, but it too has failed validation.

Recently, I conducted another survey of the scientific literature to see if I had missed any important studies involving population size and genetic diversity. Again, I was unable to find any studies that demonstrated the validity of any of the three approaches used to measure population size. Instead, I found three more studies indicating that when genetic diversity was measured for animal populations on the verge of extinction, it was much greater than expected, based on the predictions derived from the mathematical models.4

The Surprisingly High Genetic Diversity of White-Tailed Deer in Finland

Of specific interest is a study published in 2012 by researchers from Finland. These scientists monitored the genetic diversity (focusing on 14 locations in the genome consisting of microsatellite DNA) of a population of white-tailed deer that were introduced into Finland from North America in 1934.5 The initial population consisted of three females and one male and since then has grown to between 40,000 and 50,000 individuals. This population has remained isolated from all other deer populations since its introduction.

Though the researchers found that the genetic diversity of this population was lower than for a comparable population in Oklahoma (reflecting the genetic bottleneck that occurred when the original members of the population were relocated), it was still surprisingly high. Because of this unexpectedly high genetic diversity, size estimates for the initial population would be much greater than four individuals. To put it another way, this population size method fails validation—one more time.

Why is this approach to measuring population sizes so beleaguered when the method is based on sound, well-understood principles? In Who Was Adam? (and elsewhere), I point out that the equations undergirding this method are simplified, idealized mathematical relationships that do not take into account several relevant factors that are difficult to mathematically model, such as population dynamics through time and across geography.

Recently, conservation biologists have identified another factor influencing genetic diversity that confounds the straightforward application of the equations used to calculate initial population size: long generation times—that is, animals with long generation times display greater-than-anticipated genetic diversity, even when the population begins with a limited number of individuals.6

This finding is significant when it comes to discussions about Adam and Eve’s historicity. Human beings have long generation times—longer than white-tailed deer. From a creation model perspective, these long generation times help to explain why humanity displays such relatively large genetic diversity, even though we come from a primordial pair. And it suggests that the initial population size estimates for modern humans are likely exaggerated.

So did humanity originate as a population or a primordial pair?

The claims of some geneticists and evolutionary biologists notwithstanding, it’s hard to maintain that humanity began as a population of thousands of individuals because the methods used to generate these numbers haven’t been validated—in fact, work in conservation biology makes me wonder if these methods are trustworthy at all. Given their track record, I would never have used these methods when I worked in R & D to make a business decision.

Resources

Endnotes

  1. For a recent and accessible discussion of these methods, see Dennis R. Venema and Scot McKnight, Adam and the Genome: Reading Scripture after Genetic Science (Grand Rapids: Brazos Press, 2017), 45–48.
  2. Fazale Rana with Hugh Ross, Who Was Adam? A Creation Model Approach to the Origin of Humanity (Covina, CA: RTB Press, 2015), 349–53.
  3. Ibid.
  4. Catherine Lippé, Pierre Dumont, and Louis Bernatchez, “High Genetic Diversity and No Inbreeding in the Endangered Copper Redhorse, Moxostoma hubbsi (Catostomidae, Pisces): The Positive Sides of a Long Generation Time,” Molecular Ecology 15 (June 2006): 1769–80, doi:10.1111/j.1365-294X.2006.02902.x; Frank Hailer et al., “Bottlenecked but Long-Lived: High Genetic Diversity Retained in White-Tailed Eagles upon Recovery from Population Decline,” Biology Letters 2 (June 2006): 316–19, doi:10.1098/rsbl.2006.0453; Jaana Kekkonen, Mikael Wikström, and Jon Brommer, “Heterozygosity in an Isolated Population of a Large Mammal Founded by Four Individuals Is Predicted by an Individual-Based Genetic Model,” PLoS ONE 7 (September 2012): e43482, doi:10.1371/journal.pone.0043482.
  5. Kekkonen, Wikström, and Brommer, “Heterozygosity in an Isolated Population.”
  6. Lippé, Dumont, and Bernatchez, “High Genetic Diversity and No Inbreeding”; Hailer et al., “Bottlenecked but Long-Lived.”

Subjects: Adam & Eve, Creation & Genesis, Human Origins