Sunday, October 28, 2018

Adam and Eve: Genetic Evidence

When I was growing up my mother would often say to me, "All your life you'll have to do things you don't want to do." This post may fall into that category of doing something I don't really want to do but I probably should do. One of my readers asked if I could comment on the genetic evidence from DNA analysis supporting an historical Adam and Eve. I think that is a great question and a very important question since the story of Adam and Eve is central to the biblical narrative. Many of my readers have affirmed that my writings and videos have made a strong case that God used the big bang as his method of creation and that both the record of nature and the biblical record support a 14 billion year old universe. My readers have indicated to me that I seem to be able to explain complex subjects in simple terms, and so I have been asked to explain the scientific evidence about human origins in simple terms. I'm certainly willing to discuss what I know about this subject, but as a particle physicist and not a geneticist I am far from an expert on understanding and critiquing genetic evidence. When I write about physics I'm confident that I can separate good arguments and good scientific analysis from poor arguments and analysis. When I write about genetics, I'm not sure I can always separate the good signal from the background noise. Nevertheless, in response to the wishes of my readers I will delve into the subject of Adam and Eve. In this post I'll talk about some of the scientific and genetic evidence regarding human origins and in the next posts I'll discuss some other options that may reconcile the scientific evidence with the biblical record and also examine some of the theological issues dealing with Adam and Eve.

As an introduction let's discuss some very basic information about DNA and genetics. Just about every cell in every person's body has the same DNA, which consists of a long series of atoms wrapped in a double helix structure. Each person's DNA is the genetic code that makes them who they are physically. Your DNA is a composed of segments called genes that determine your eye color, your skin color, your height (mostly), and everything else physically about you. Genes are organized into groups or packages called chromosomes. Each person's genes are passed to them from their mother and father who got their genes from their mother and father, and so on. Consequently, your genes provide a record of your ancestral history. That is why DNA testing can tell you where your ancestors came from or who you are related to, and whether or not you were actually separated from a long lost sibling at birth. Certain DNA, called mitochondrial DNA, is passed down only from a person's mother so gives information about a person's female ancestry, and other DNA testing, called Y chromosomal DNA testing, gives information about a person's male ancestry. In general, we all trust that genetic DNA analysis is fairly accurate. After all, many of us have had genetic testing done just to find out where in the world our ancestors are from.

DNA testing has shown that all humans are related to a single ancient mother and also to a single ancient father, both of whom may have lived very roughly about 150,000 years ago, but with huge uncertainties in that date (with most uncertainties tending to push the date farther back in time). This discovery of a common mother and father of all humans may seem to completely support and vindicate the story of Adam and Eve, and I ultimately think it does as I will explain later, although their existence 150,000 years ago may seem like a long time ago to some people. However, according to scientists who do genetic testing, there is still a major problem in fitting this genetic understanding to an actual historical first couple that has to do with genetic diversity.

Genetic diversity is a measure of how different are the genes of different individuals. Your genes are going to be very similar to your siblings but quite different from those of someone who you are not recently related to. Genes diversify for many reasons but can change due to simple random mutations which means that something happens, maybe a copying error when the gene is replicated, that slightly changes the gene. The rate of gene mutation is fairly well known so the amount of genetic diversity that occurs over a period of time can be fairly well estimated. Genetic scientists claim that the amount of genetic diversity we see today across the human population is not compatible with having only a single couple who existed within the last few hundred thousand years and is the genetic mother and father of all humans. The general consensus is that the first humans consisted of a small population of about one thousand to a few thousand individuals who existed about 100,000 years ago (with uncertainties of about plus or minus 50,000 years) in order to produce the genetic diversity we see now.

Since I'm not a biochemist or geneticist I can't confirm the accuracy of these numbers and whether or not a few thousand individuals are required. But I do know that there seems to be little science that actually corroborates some of the assumptions that go into the calculation of the original number of humans. For readers who are interested in more details about some of the challenges to these conclusions I refer you to Dr. Fuzale Rana of Reasons to Believe who has written much on this subject including Adam and Eve: A Primordial Pair or Population, and Were They Real? A Scientific Case for Adam and Eve. In the next paragraphs I'll summarize some of Dr. Rana's arguments and comment on his conclusions.

The first thing to note is that the rate at which genes diversify is based on simple mathematical models that have not been verified to the level of their accuracy. I know in physics it is common to start with simple models and when those models don't accurately describe the data, to revise the models and add complexity to them to more accurately describe what we see in nature. Unfortunately, in genetics that feedback mechanism of making the model more complex to meet the data has not been done (and maybe cannot be done very easily). So the predictions of the models are believed even though the models are known to be idealized and simplified without independent validation. Such a model would not be accepted as valid in the more rigorous mathematical scientific discipline of physics that I work in.

In addition, there are reasons to believe that the simple models are actually not accurate. For instance, in 1957 a single pair of Mouflon sheep were left on one of the Kerguelen islands near the Antarctic circle. In 2007 the genetic diversity of the ancestors of these sheep was tested and found to be about four times greater than the simple mathematical models predicted. Other tests of these simplified mathematical models have failed as well. A small population of white-tailed deer introduced into Finland were tested for their genetic diversity in 2012 and again, found to have much more diversity than expected based on the simple models. Dr. Rana claims that there are no published peer-reviewed articles that actually validate that the simple mathematical models are precisely valid. Dr. Rana states that in his latest search throughout the scientific literature, "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."1

Based on all of the genetic evidence, the conclusion from science is consistent with the biblical idea that humans have descended from one male and one female, and that both lived maybe 150,000 years ago or so. Although most genetic scientists would argue that those two lived among a population of a few thousand and probably lived at different times, the scientific models on which those latter conclusions are based seem to me to be too simple without precise validation. Consequently, it seems that the current confirmed scientific evidence does indeed point to a conclusion that is in alignment with the biblical record of a historical Adam and Eve being the genetic ancestors of modern humans.

None of this discussion has anything to do with the original creation of Adam and Eve. Progressive old earth creationists would advocate that Adam and Eve were a special creation by God without any evolutionary pre-human ancestors while evolutionary creationists would argue that Adam and Eve were created by God through an evolutionary process from pre-human ancestors.

But even with the recognition that scientific inquiry confirms a genetic Adam and Eve that I believe could be the first two humans and the genetic ancestors of all humanity there are other factors and options that must be considered and discussed, which will be addressed in the upcoming blogs.



  1. As you confessed, you're not a genetic biologist. That would explain why you totally misunderstand the statement that "DNA testing has shown that all humans are related to a single ancient mother and also to a single ancient father." DNA analysis has shown that all mitochondrial DNA in living humans can be traced back to one female individual who lived around 150,000 years ago. This mans that the different lines of mitochondrial DNA of all the other women who lived at that time have did out, and only hers has survived, albeit mutated into many different modern strands. It also shows that all Y chromosomes in living human males can be traced back to a single male. The discovery of a previously unknown Y chromosome haplogroup in 2013 pushd back the date of "Y chromosome Adam" to betwen 200,000 and 300,000 years ago. But that doesn't mean that all our other genes are descended from those two same people: certainly not, in fact. So we're not related to "a single mother and father" - we're related to multiple different mothers and fathers, one each for each chromosome.

    1. Everything you say is compatible with my claims in this post. Unfortunately, I do understand what the DNA evidence says about common ancestry. Please show what statement in my post is incompatible with current understanding of DNA and genetics.