“Humans evolved gradually, so there was no first woman.”

The coalescence theory of populations genetics leads to the conclusion that the DRB1 polymorphism requires that the population ancestral to modern humans has maintained a mean effective size of 100,000 individuals over the 30-million-year persistence of this polymorphism. We explore the possibility of occasional population bottlenecks and conclude that the ancestral population could not have at any time consisted of fewer than several thousand individuals. The MHC polymorphisms exclude the theory claiming, on the basis of mitochondrial DNA polymorphisms, that a constriction down to one or few women occurred in Africa, at the transition from archaic to anatomically modern humans, some 200,000 years ago.

It has been proposed that modern humans descended from a single woman, the "mitochondrial Eve" who lived in Africa 100,000 to 200,000 years ago. The human immune system DRB1 genes are extremely polymorphic, with gene lineages that coalesce into an ancestor who lived around 60 million years ago, a time before the divergence of the apes from the Old World monkeys. The theory of gene coalescence suggests that, throughout the last 60 million years, human ancestral populations had an effective size of 100,000 individuals or greater. Molecular evolution data favor the African origin of modern humans, but the weight of the evidence is against a population bottleneck before their emergence. The mitochondrial Eve hypothesis emanates from a confusion between gene genealogies and individual genealogies.

Our analyses support a model in which a weakly structured ancestral Homo population gave rise to modern humans without requiring a single, isolated founding population. We infer that the earliest population divergence detectable in present-day humans occurred around 120–135 thousand years ago, but before this time, ancestral Homo populations within Africa were subdivided yet maintained considerable gene flow for hundreds of thousands of years. Under this model, there is no point in time at which the ancestry of all modern humans passes through a single small population or a single couple.

Human evolution is a long process that began in Africa probably in the late Miocene Epoch and continued through the Pliocene and into the Pleistocene, spanning roughly 6 million years or more. Over this time, many different hominin species existed, often overlapping in time and space. Because species arise through gradual genetic change in populations, there is no clear demarcation between ‘non-human’ ancestors and anatomically modern humans in the sense of a single first individual.

Human evolution took place as new genetic variations in early ancestor populations favored new abilities to adapt to environmental change. Evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Over many generations these changes accumulate in populations, rather than appearing suddenly in a single ‘first’ individual.

Discussing the complexity of the human family tree, the article says: “Human evolution is not a linear progression from one species to another but a branching bush with many side branches. Over time, one population of early Homo gradually accumulated traits that we recognize as modern, but there is no clear boundary between ‘non-human’ ancestors and ‘human’ descendants.” This reinforces the scientific view that there is no identifiable first human individual, male or female.

Mitochondrial Eve is the name given by scientists to the woman who is the most recent common ancestor of all living people today when you follow their maternal line. She was not the first human woman, nor was she the only woman alive at the time. She lived within a population of many thousands of women, men and children, and other women living then also have descendants alive today through their sons and daughters, just not in an unbroken female line.

Summarizing Dawkins’s explanation, the article states: “you can never put your finger on the very first human being, a proverbial Adam and Eve… there is no single generation in which one can point to a demonstrably new species sprouting from another. It’s just that over multiple generations, the morph does take place.” Dawkins uses this to argue that the common idea of a first man or first woman is biologically incoherent under gradual evolution.

The human family tree shows many species of early humans existing at the same time, often in overlapping regions. Anatomically modern Homo sapiens appear in the fossil record about 300,000 years ago in Africa, but they emerge from earlier Homo populations rather than from a single pair of individuals. Evolutionary change occurs within populations over many generations, so there is no clear boundary where a first man or first woman suddenly appears.

On the standard evolutionary account, new species arise gradually through the accumulation of genetic changes in populations. Because speciation is a population-level process, there is typically no single individual that can be picked out as ‘the first member’ of a new species. Any individual human would have had parents and grandparents that were only trivially different from them, and differences accumulate over many generations rather than appearing all at once.

Speciation is usually a gradual process, driven by the accumulation of genetic differences in populations over time. As these differences build up, populations become more and more distinct until they no longer interbreed. Because this process is continuous, there is no single generation that can be labeled as the first of a new species. Any attempt to identify a ‘first’ human individual faces this fundamental problem of continuity.

The process of evolution did not happen all at once. Different features evolved at different times and rates, and not always in the same direction. Our species, Homo sapiens, evolved from earlier species of Homo through a series of small changes that accumulated over many thousands of generations. There is no single moment we can point to as the beginning of ‘modern’ humans; instead there is a mosaic of traits that appeared gradually.

The page describes human evolution as “the biological process by means of which the human species has developed… under continuous construction.” It notes that hominids “separated from the chimpanzee group some 7 million years ago” and emphasizes that “since it separated from the chimpanzees, the human family has not evolved in a straight line, but has subdivided into branches based on a common tree… Many groups coincide at the same time and in the same space.” This branching, gradual view implies there was no single moment when a first human woman appeared.

The data clearly and strongly suggests that it was not from a single couple; our species diverged as a population. Numerous studies analyzing many different genes all point to a bottleneck. However, these studies are all clear: during the bottleneck, there were several thousand individuals, not two. The multiple shared categories make it clear that although a human population bottleneck occurred, it was definitely never as small as two.

“For speciation to occur, two new populations must be formed from one original population, and they must evolve in such a way that it becomes impossible for individuals from the two new populations to interbreed. Speciation is often a gradual process: over many generations, populations become more and more different. There is no clear-cut boundary where we can say that one generation was one species and the next generation was another.”

Speciation, the formation of one or more new species from an existing species, usually involves the gradual accumulation of genetic differences between populations. Because this divergence occurs over long periods of time, there is no precise generation that can be singled out as the origin of the new species. Instead, the transition from one species to another is spread over many generations in which intermediate forms exist.

Modern human genetic diversity and coalescent analyses indicate that our species (Homo sapiens) has not passed through a bottleneck of just two individuals in the last few hundred thousand years. Instead, estimates of effective population size for ancestral Homo sapiens are typically in the thousands. Under such conditions of gradual divergence and sizable breeding populations, evolutionary biology does not predict a discrete, uniquely identifiable ‘first woman’ who was human while her mother was not.

I’m not clear though about how genetics shows that the initial population was definitely more than 2 (Adam+Eve)… This is because we could also say that genetic evidence shows that humans descended from about a billion people 200 years ago. And when we greet the several thousand ancestors from 150,000 years ago one wonders… whether they had parents, whether they had common ancestors. The discussion highlights that population genetics deals with effective population sizes and common ancestors of gene copies, not with a unique first couple, and that many individuals in overlapping generations contribute to present-day ancestry.

The article argues against evolutionary gradualism: “Scripture clearly teaches that Adam was the first man (1 Corinthians 15:45), specially created by God from the dust of the ground (Genesis 2:7), and that Eve was created from Adam’s rib (Genesis 2:21–22). Humanity did not evolve from pre-human animals over millions of years.” It therefore implies a first man and first woman created as distinct individuals, contradicting the idea that evolution precludes a first woman.

Mitochondrial DNA (mtDNA) is inherited only from the mother, and analysis of mtDNA worldwide has shown that all humans are descended from a single woman who lived only thousands of years ago, not hundreds of thousands. This so-called ‘Mitochondrial Eve’ is consistent with the Bible’s account of a literal first woman from whom all people descend, rather than a long history of gradual evolution from ancestral populations.