“What you seem to be implying, however, is a hitherto undiscovered mechanism whereby the genome takes control of its own evolution, somehow sensing the right time to bring about change.” Greg Bear, Darwin’s Radio, p. 272
“All human beings may be descended from just TWO people…study suggests” was the Daily Mail headline that caught my eye while I was browsing Drudge last November. (Sorry, I do admit to reading Drudge, daily.)
Having learned to distrust newspaper accounts of new physics developments, I decided to read the original paper by Stoeckle and Thaler that spawned this and similar popular accounts: Using a barcoding technique to define variation in mitochondrial DNA of humans and many other species, they conclude
… the extant [human] population, no matter what its current size or similarity to fossils of any age, has expanded from mitochondrial uniformity within the past 200,000 years.—M.Y. Stoeckle and D.S. Thaler, “Why should mitochondria define species?” ¹
What could produce such “mitochondrial uniformity” 200,000 years ago? Here are two possible explanations:
- all humans descended through the female line from a single female
- the population from which humans descended was very small, a so-called “evolutionary bottleneck.”
Ann Gauger has given a detailed analysis of Stoekle’s and Thaler’s paper here, which need not be repeated in this post. Please go to the web-page linked above for a detailed explanation of how evolutionary bottlenecks occur. In brief, we can say that when the population becomes small, random sampling of the gene pool no longer represents the genetic variation.²
MORE BACKGROUND: MITOCHONDRIAL EVE
Stoeckle and Thaler were not the first evolutionary geneticists to use mitochondrial DNA to trace our ancestral beginnings. In 1987 Cann, Stoneking and Wilson proposed a “Mitochondrial Eve” hypothesis, that all humans are descended from an African lady who lived some 100,000 to 200,000 years ago.
The advantage in using mitochondrial genes as a tracer is that they propagate only through the female line, as shown in the image below. However, it’s important to realize that Mitochondrial Eve might have contributed only a small amount to our gene pool, given that there would have had to be many, many other great-great-……-great grandparents.
Mitochondrial descent from one female through 5 generations; the different colors denote different genotypes; from Wikimedia Commons
The Mitochondrial Eve hypothesis has been criticized by evolutionary geneticists who argue that “bottlenecks” (small population sizes) lead to minimal genetic variation and thus lower survival of species. Francisco Ayala has examined the variation in the gene DRB1 and concludes the variation is too large to admit of a small population (bottleneck) as ancestors. (See here.)
Ayala’s calculations have been criticized as being biased and based on assumptions that don’t apply. Certainly his conclusions do not agree with those of Stoeckle and Thaler. But are there other possibilities?
AN EVOLUTIONARY PUZZLE
The notion that such randomly, undirected, simultaneous appearance of favorable mutations is implausible has also occurred to others, not all of whom believe in God: Thomas Nagel, Stuart Kauffman, Michael Behe, Stephen Meyer, among others. Nagel proposes a Teleological Principle as the motive force for evolution. Kauffman’s approach is spontaneous self-organization. Behe and Meyer would replace the neo-Darwinian model for evolution by Intelligent Design (ID). I would argue for ID as a philosophic or metaphysical proposition, but not as a scientific one. (See here.)
DARWIN’S RADIO: HOW EVOLUTION OCCURS?
As is often the case, science-fiction sometimes gives answers (not always satisfying) to theological questions. A classic science-fiction novel, Darwin’s Radio, by Greg Bear, answers the question “What is the mechanism by which the Creator might form new species?”. Whether Bear’s mechanism is a possible one (or testable), I won’t judge, since I have minimal expertise in molecular biology. However, it is an interesting idea, so let’s see what he has to say.
I’ll not summarize the plot of Darwin’s Radio; that is done elsewhere, and if you haven’t read the book (on the Best-Seller list of the NY Times for many weeks) and want to do so, it would be a spoiler. The article linked above discusses the molecular biology on which the plot is based, so I’ll not repeat that here.
A RETROVIRUS CAUSES EVOLUTION
Here are the salient points. (WARNING: semi-spoiler if you want to read the book.) HERV (Human Endogenous RetroVirus) cause an epidemic: the HERV is transmitted by men to women with whom they have a “steady” sexual relation; the virus causes spontaneous abortions, but the aborted fetus carries an egg that produces a second pregnancy. The child born in this second pregnancy has unusual and different capabilities, including parallel processing in the brain, pherenomes and facial pigmentation changes to convey emotional responses—in short a new species.
That such an evolutionary change has occurred before is shown in the novel by the discovery of a prehistoric couple preserved in a glacial cave; the male and female are some 15000 years old, and apparently Neanderthals–but there is also a baby, which is apparently Homo Sapiens. The discovery in this prehistoric couple of the HERV that occurs in the modern epidemic suggests that this was the cause of change to Homo Sapiens from early forms. (In this Bear make a paleontological error; Neanderthals and Homo Sapiens were both present over a fairly long time period, and various human races contain up to 3% of Neanderthal genes.)
So, Bear’s suggestion is that somehow the mechanism by which discontinuous jumps to a new species occur is a concerted epidemic carried by an endogenous retrovirus (ERV), contained in the so-called junk portion of DNA. An important question (not answered in the novel) is “who sends the signal for Darwin’s Radio to sound?”, i.e. what causes this epidemic to occur over a limited time span? Is it God, or is the time span set by some Designer, so that after some period of time, the mutations will occur?
My own scientific expertise is not in molecular biology, so I welcome criticisms of Bear’s speculative mechanism for speciation and suggestions for alternatives.
BIOLOGICAL MONOGENESIS VERSUS THEOLOGICAL MONOGENESIS
The discussion above has to do with biological monogenesis versus polygenesis. Or, in plainer language: did humanity descend from a single pair of humans, Adam and Eve, or from many pairs? Monogenesis is a crucial piece of Catholic dogma because from this follows the dogma of Original Sin.
However, It is difficult for me to reconcile what we know from physical anthropology and genetics with biological monogenesis. Indeed, Pope St. John Paul II has argued that it is the creation of the soul that endows the form with humanity:
“Pius XII underlined the essential point: if the origin of the human body comes through living matter which existed previously, the spiritual soul is created directly by God…” Pope St. John Paul II, Address to Pontifical Academy of Sciences:”On Evolution”.
¹Stoeckle and Thaler strongly reject the interpretation given by the Daily Mail writer: in a note added to their paper December 4, 2018, they declare:
This study is grounded in and strongly supports Darwinian evolution, including the understanding that all life has evolved from a common biological origin over several billion years. This work follows mainstream views of human evolution. We do not propose there was a single “Adam” or “Eve”. We do not propose any catastrophic events.
²Consider the following example: a bottle contains 100,000 colored marbles, 50,000 red, 30,000 green and 20,000 blue. If you take a large enough random sample from that bottle (a few hundred, say) then the proportions of red: green:blue are likely to be close to 5:3:2. If your sample size is small (the bottleneck size), than you are quite likely to get samples in which there are no blue marbles. For example for 5 marbles drawn, the probability would be about 32% that no blue marbles would show.