Mosaic Eve: Mother of All (Part 2)
In Part 1 of “Mosaic Eve,” I set the stage for considering how God might introduce enough diversity into the human population from a founding pair to account for the genetic diversity we observe today. Could one individual, or a couple, created by God to populate the entire human race, harbor diversity that is consistent with what we know of biology and physiology, yet, in a sense, that is historically unique, like the virgin birth? In part 1, I articulated RTB’s approach of considering data primarily drawn from nature (science) but consistent with observations drawn from Scripture. One constraining factor in our integration of data that’s consistent with general scientific premises, is that God’s creation operates with reliable regularity, and the physical laws and constants that describe natural processes today are, and have been, consistent throughout time and space.1
I am not the first to posit that creating the founding couple with a mosaic of gametes (or gametogonia, cells that give rise to sperm and eggs/oocytes), each with a unique genotype, is one way to provide sufficient diversity in the extant human population. However, I would like to limit my speculation of the type of mosaicism in the founding pair based on what we know of human biological development and scriptural considerations. Although this speculative model is set forth with these two factors in mind, limiting the type of mosaicism may also help set parameters for computationally modeling human population diversity based on an historical sole-progenitor pair at its base.
Female Germ Cells—Reproductive Biology 101
In normal, healthy, female development, a newborn is born with an excess of fully formed oocytes. In utero, a developing female embryo’s germ cells (also known as gametes, eggs, or oocytes) begin forming around 6-7 weeks gestation. The number of eggs may reach 6-7 million cells per ovary during embryonic development. At the time of birth a newborn baby girl will have 1-2 million eggs (primary oocytes in meiotic arrest), each surrounded by follicular epithelial cells forming primary follicles. Loss of primary (and advanced stage) follicles occurs throughout development, and by the time a woman completes puberty and reaches reproductive age this number will have dropped to approximately 250,000 follicles per ovary. With the onset of a regular menstrual cycle, a nearly linear decrease of the follicle cell count ensues. The rate of loss increases around age 40 and, at roughly 50 years of age, follicles are no longer present and menopause begins.
During menstruation, some primary oocytes exit meiotic arrest, divide, and produce a secondary oocyte (and polar body). In the ovulation stage, one mature (graafian) follicle erupts and releases a secondary oocyte made available for potential fertilization. Healthy oocytes are diploid cells containing two maternal copies of each chromosome (autosomes 1-22 and X chromosome). However, concurrent with fertilization, the ovum undergoes meiosis II, resulting in a zygote with only one copy of the maternal chromosomes (and one copy of the paternal chromosomes).
Mosaic Eve’s Population Effect
The Bible seems to indicate that Eve was created in a postpubescent state. We can infer that, as a special de novo creation at the headwaters of humanity, Eve’s eggs were not produced through normal embryonic and prepubescent development. Thus, they were not limited by these developmental constraints. In other words, as God created the adult Eve, he could have easily formed each of her primary oocytes (within the primary follicles) with a unique genotype different from any other in her repertoire of hundreds of thousands of eggs.
If this were the case, then each of Adam and Eve’s offspring would have had a unique maternal chromosome paired with one of two paternal chromosomes. The level of genetic diversity would be constrained in the F1 (first generation) population by the number of (nonidentical twin) offspring.
Estimating the number of offspring introduces two other factors for consideration: the duration of Eve’s (female) reproductive lifespan (the difference between the age at menarche and the age at menopause) and the number of children (or pregnancies) possible for a single mother over her reproductive lifespan. One 2017 study found the average (mean) ±SD (standard deviation from the mean) duration of reproductive lifespan for a cohort of 58,927 women who experienced natural (i.e., nonsurgical) menopause = 37.5±3.9 years. 2
And as to the number of pregnancies, this is a little more difficult to estimate but I’ll take into consideration the duration of reproductive lifespan (estimated above).
According to lore, one Russian peasant woman, Mrs. Feodor Vassilyev, gave birth to 69 children (27 pregnancies in a 40-year period, 1725–1765)! I don’t know about you, but I was shocked and highly skeptical to hear this number. As others have pointed out and all mothers know, pregnancy places extreme demands on a woman’s body. So, one woman is unlikely to survive the toll for birthing so many (taking multiple births into consideration). Other more recent reports requiring perhaps less skepticism include a Ugandan woman who has given birth to 44 children (all multiple births) by the age of 36 years. Ms. Mariam Nabatanzi was pregnant 15 times over a 23-year span (ages 13–36). A couple from Maine reportedly produced 22 children, all single births, over a 30-year period (1882–1911). These two reports suggest that productive pregnancies possibly occur every 16–18 months for an individual woman. Over an average 37.5-year reproductive lifespan, estimating one pregnancy every 16–18 months would result in 25–28 pregnancies.
Many other reports of births in excess of 20 children to individual women abound, but the number of pregnancies involved is unclear in these reports. Still, based on the aforementioned observations, it is not unreasonable to postulate that Eve may have realistically given birth following 25–30 pregnancies over a 35–40-year period. Discounting any multiple births, this would set the number of alleles in an F1 human population conservatively at 25 (maternally derived alleles) plus 2 (paternally derived alleles) and set human population genetics at a TMR27A (time to most recent 27 alleles) time point.3 Although I have made conservative estimates, obviously such speculation is open to adjustment or criticism.
Adam as a Source of Greater Genetic Diversity
In contrast to female biology, male germ cells (spermatozoon or sperm cells) are produced only after puberty. Spermatogonia (over 1 billion in both testicles) form the basal layer of the germinal epithelium in the testes. Over a two-month period a subset of these cells progresses through various stages resulting in the ongoing production of roughly 150 million spermatids (immature spermatozoon) per day. A mosaic Adam model would require mosaicism within cells (spermatogonia) in a single tissue (germinal epithelium).
Examples of genetic mosaicism at tissue and organ levels in a single individual are rare but known to occur and are actually better thought of as chimerism (not because of their source, but because of the complete difference in genotype of cells sharing a similar tissue or organ compartment).4 In chimerism, genotypes of certain cellular populations are different from the surrounding cellular genotypes. So it is possible, though perhaps less biologically straightforward, to suggest Adam may also have contributed gametes of unique genotypes. If so, this would result in doubling the possible number of alleles available at the founding generation of human population modeling (TMR54A). Although this type of mosaicism (or chimerism) is certainly within a Creator’s purview, it seems, at least to me, less straightforward and perhaps unnecessary.
Any Scriptural Insights?
Others have asked me why I speculate on a mosaic Eve rather than on a mosaic (or chimeric) Adam and Eve. My speculation is built on two parallel observations. First, all healthy women have a full complement of follicles harboring primary oocytes in meiotic arrest at the time of reproduction. As adult females our egg repertoires are set. God could have created Eve de novo with a mosaic repertoire, consistent with what is known of female biology. Second, the Hebrew Scriptures seem to suggest a unique (in the sense that nothing similar of Adam is proclaimed) attribute to Eve at the onset of humanity. Genesis 3:20 refers to Eve as “the mother of all the living.” This strikes me as a strange phrase to arise from a patristic culture that is putting forward a unique couple at the headwaters of humanity. Why single Eve out? Why not state Adam as the father of all living, or the two together, as the parents of all living? In my estimation, If Adam and Eve were the sole-progenitors of the human race, a mosaic Eve is the most reasonable and biologically straightforward way to speculate and introduce genetic diversity into an adult pair with as little tweaking of normal biology comparative to modern human biology and one that concords with observations drawn from Scripture.
Solving Other Problems
Postulating a mosaic Eve solves other potential problems. God need not direct particular biological or physiological events, nor direct genetic recombination events, nor direct mating selection, etc. In fact, no special intervention by God is required in the early days of human reproduction other than the special creation of a reproductive pair. One has to ask, why on earth wouldn’t God have created Eve with such a capacity if a diversity within the human population was his intention all along? Not doing so suggests shortsightedness on God’s part. A mosaic Eve provides not just genetic diversity but releases the F1 generation of the early human population from inbreeding depression. This would mean the early human population need not have the same safeguards as current populations to avoid reproduction between sibling pairs or close cousins. (This would also correlate with scriptural observations that such close relations were not explicitly prohibited prior to the Sinaitic law, cf. Leviticus 18 and Deuteronomy 27.)
Counting Chromosomes and Looking for Signs
So, does a mosaic model get us any closer to an intermediate dating for Adam and Eve, a date consistent with RTB’s sole-progenitor model? And if so, does that really solve the challenges to the RTB human origins model from modern population genetics? It may get us from TMR4A to a TMR27A or TMR54A, but what about the bottleneck at Noah? Is this the one we should focus on? And what parameters do we set there? Assuming Noah’s three sons and their three wives as the only founders for the subsequent human population this would give us TMR10A. What date would that render for the RTB human origins model?
These questions leave us with some good points for discussion (and future analyses) in our interactions with Peaceful Science. We’ll certainly be considering the confluence of scientific and scriptural data for dating a historical progenitor pair. Integrating science and Scripture can be challenging, but ultimately it’s rewarding. Learning more about our origins is obviously significant but it’s also exciting.
For further consideration:
Among the aforementioned questions should we consider others as well? For example, should we expect any genetic signature in our extant population? Would we expect a Y coalescence more recent than an X, autosomal, or mtDNA (mitochondrial DNA) coalescence, and are our analyses sensitive enough to detect such differences? Should we expect more degeneration of Y chromosomal sequences in comparison to other chromosomes in the human genome?
- This position is in contrast to some (YEC) creationist assumptions that speculate that the physical laws observed today do not reflect uniformly into past processes or to current processes throughout the observable universe.
- Sylvia H. Ley et al., “Duration of Reproductive Life Span, Age at Menarche, and Age at Menopause Are Associated With Risk of Cardiovascular Disease in Women.” J Am Heart Assoc. 6, no. 11 (November 2017):e006713, doi:10.1161/JAHA.117.006713.
- A higher number (x) in TMRxA correlates with calculations for a more recent time for a founding pair harboring x heterozygous alleles.
Simonetta Verdiani et al., “An Unusual Observation of Tetragametic Chimerism: Forensic Aspects,” International Journal of Legal Medicine 123, no. 5 (September 2009): 431–35, https://doi.org/10.1007/s00414-009-0332-0 and Kristen Chen et al., Chimerism in Monochorionic Dizygotic Twins: Case Study and Review American Journal of Medical Genetics Part A (March 2013): 161A:1817–24, doi:10.1002/ajmg.a.35957.