Try debating with a creationist on social media and before long you will be challenged to explain how sexual reproduction evolved, because there must have been a first male and a first female. A regular form of this, betraying the abysmal ignorance of the creationist, is the childish attempt at a "Gotcha!" with, "How long did the first man have to wait for the first woman to evolve?"
Like so many creationist preconceptions about what evolution is and what evolutionary biologists claim, this assumes that each species somehow evolves without ancestry, so everything about it must have arisen spontaneously in a single individual or, in this case, in a single couple. There is no awareness of inheritance from common ancestors, nor of the slow accumulation and honing of traits over time. Presumably, the questioner thinks adult men and women being magicked into existence without parents is a perfectly rational belief.
In reality, sexual reproduction did not begin with men and women. A form of sex almost certainly arose long before animals, among single-celled eukaryotes, and need not have involved anything recognisable as male and female. At its simplest, sex is the mixing of genetic material from different individuals. The interesting question, from the point of view of evolutionary biology, is not where the first man and first woman came from, but what advantage genetic mixing had over cloning or other asexual forms of reproduction, such that it became the predominant, although far from exclusive, method of reproduction among complex organisms.
Now two researchers from the Department of Zoology at the University of Cambridge, UK, believe they have part of the answer, and have just published their findings in Nature Ecology & Evolution. The paper, by Dr Emily G. Mitchell and Professor Andrea Manica, examines how reproductive mode affected competition, dispersal and diversity among Ediacaran animal communities. It is accompanied by a research news item from the University of Cambridge.
The Ediacaran Period, roughly 635-539 million years ago, saw some of the earliest known large animals. Many of them would look nothing like any modern animal: they were sessile, lacked mouths and obvious digestive systems, and probably absorbed nutrients directly from the surrounding seawater. In the relatively benign conditions of the Ediacaran oceans, with limited predation and reduced competition, there was less pressure for rapid diversification. As a result, these early animal communities appear to have changed only slowly for millions of years before the later burst of diversity that preceded and fed into the Cambrian radiation.
But, as they began to colonise the shallower seas and coastal regions, the Ediacaran biota would have encountered increasingly unstable conditions with tides, storms and fluctuating temperatures and nutrient levels, so there would have been competition and selection pressure to adapt to these more hostile conditions. And this is what we see in the fossil record as the Ediacaran biota produced a second wave of more diverse forms, leading eventually to the 'Cambrian Explosion'.
Previous work has shown that some of these Ediacaran organisms reproduced asexually by sending out stolons or runners, rather like strawberry plants do today. Their offspring were clones, physically connected to the parent colony and genetically very similar. That can work well in a stable environment, but it has a serious evolutionary limitation: it restricts the mixing of genes from different lineages. Beneficial mutations that arise in separate clonal lines cannot easily be combined in the same genome, so lineages compete with one another instead of pooling their evolutionary gains.
Sexual reproduction changes that. It does not create evolution by magic; it provides natural selection with more combinations on which to act. Beneficial alleles that arise in different lineages can be brought together in the same genome instead of being trapped in competing clonal lines. This is the Fisher-Muller advantage of recombination: sex can turn evolutionary change from a slow serial process into a more rapid parallel one.
(Skip the next technical section if your maths understanding is like mine. Basically, it shows mathematically why multiple beneficial mutations accumulate more quickly than single such mutations, in a sexually reproducing species)
The point can be illustrated with a simple selection model. Suppose a genotype carrying one beneficial allele has fitness \(1+s\), where \(s\) is the selective advantage. If its frequency in the population is \(p_t\), then after one generation of selection:
\(
p_{t+1}=\frac{p_t(1+s)}{1+s p_t}
\)
The log-odds of that genotype therefore increase each generation by:
\(
\log\left(\frac{p_{t+1}}{1-p_{t+1}}\right)=\log\left(\frac{p_t}{1-p_t}\right)+\log(1+s)
\)
So the approximate time needed for that genotype to rise from an initial frequency \(p_0\) to a later frequency \(p_f\) is:
\(
t_1=
\frac{
\log\left(\frac{p_f(1-p_0)}{p_0(1-p_f)}\right)
}{
\log(1+s)
}
\approx
\frac{1}{s}
\log\left(\frac{p_f(1-p_0)}{p_0(1-p_f)}\right)
\)
Now suppose recombination brings together \(k\) beneficial alleles of similar effect \(s\) into the same genotype. If their effects are approximately multiplicative, the fitness of that genotype is:
\(
W_k=(1+s)^k
\)
Its effective selective advantage is therefore:
\(
S_k=(1+s)^k-1 \approx ks
\)
for small values of (s). The time for this multi-benefit genotype to spread over the same frequency range is then:
\(
t_k=
\frac{
\log\left(\frac{p_f(1-p_0)}{p_0(1-p_f)}\right)
}{
\log\left((1+s)^k\right)
}
=
\frac{t_1}{k}
\)
In this simplified case, a genotype carrying two beneficial alleles spreads at roughly twice the rate of one carrying only a single beneficial allele; a genotype carrying three spreads at roughly three times the rate, and so on. More generally, if the beneficial alleles have different effects \(s_1,s_2,\ldots,s_k\), then:
\(
W=\prod_{i=1}^{k}(1+s_i)
\)
and:
\(
t \approx
\frac{
\log\left(\frac{p_f(1-p_0)}{p_0(1-p_f)}\right)
}{
\sum_{i=1}^{k}s_i
}
\)
The log-odds of that genotype therefore increase each generation by:
So the approximate time needed for that genotype to rise from an initial frequency \(p_0\) to a later frequency \(p_f\) is:
Now suppose recombination brings together \(k\) beneficial alleles of similar effect \(s\) into the same genotype. If their effects are approximately multiplicative, the fitness of that genotype is:
Its effective selective advantage is therefore:
for small values of (s). The time for this multi-benefit genotype to spread over the same frequency range is then:
In this simplified case, a genotype carrying two beneficial alleles spreads at roughly twice the rate of one carrying only a single beneficial allele; a genotype carrying three spreads at roughly three times the rate, and so on. More generally, if the beneficial alleles have different effects \(s_1,s_2,\ldots,s_k\), then:
and:
Formulae supplied by ChatGPT 5.4 Thinking.
This is why sex matters. In an asexual population, beneficial mutations arising in separate clonal lineages tend to compete; one lineage may eliminate the other before both advantages can be combined. In a sexual population, recombination can bring those beneficial alleles together, creating fitter genotypes on which selection can act immediately.
Evolution of gender^ From mating types to males and females. The evolution of sexual reproduction did not require a first fully-formed male and a first fully-formed female. A useful living model is provided by the volvocine green algae, a group that includes the single-celled Chlamydomonas and the colonial Volvox.The paper, by Dr Emily G. Mitchell and Professor Andrea Manica, examines how reproductive mode affected competition, dispersal and diversity among Ediacaran animal communities. It is accompanied by a research news item from the University of Cambridge:
In some simpler volvocine algae, such as Chlamydomonas reinhardtii and Gonium, the gametes are much the same size and shape. They are not usefully called male and female; they are mating types, often labelled plus and minus. This condition is called isogamy, from Greek roots meaning "equal marriage".
In other related forms, such as Eudorina and Pleodorina, the gametes differ in size. One type produces many smaller gametes, while the other produces fewer larger gametes. This is anisogamy, or "unequal marriage". It is an important intermediate stage because it shows the beginning of the division between the high-quantity strategy that becomes male, and the high-investment strategy that becomes female.
In Volvox, the distinction is clearer still. The small gametes are sperm, and the large gametes are eggs. This condition is called oogamy. It is the familiar pattern seen in animals and many plants: many small, mobile sperm competing to fertilise fewer, larger, nutrient-rich eggs.
The important point is that these are not separate acts of special creation. They are variations on a reproductive theme found within a related group of organisms. The sequence from isogamy to anisogamy to oogamy shows how two mating types can evolve gradually into the familiar distinction between male and female. There was no first man waiting for the first woman; there were populations in which reproductive cells became progressively specialised over evolutionary time.
A lack of sex held back life’s diversity for millions of years
The way that Earth’s first animals reproduced held back life’s diversity for millions of years, until stress and competition led to the development of sexual reproduction, which in turn accelerated the pace of evolution.
Researchers from the University of Cambridge studied fossils from the oldest-known animals on Earth, dating from 574 million years ago, and found that asexual reproduction slowed the pace of evolution to a crawl, since it limited competition between different groups.
Their results, reported in the journal Nature Ecology and Evolution, could help explain a longstanding puzzle in palaeontology: why animal life appeared on Earth but then barely changed for millions of years, before a second wave of diversification gave evolutionary progress a major boost.
After billions of years of microbial life, during the Ediacaran period, between 635 and 539 million years ago, life exploded in size and the first animals appeared. Some of these earliest animals, such as Fractofusus, could grow as tall as two metres, although most were much smaller.
These animals looked more like ferns than any animal we would recognise today: they do not appear to have mouths, organs or means of movement, so they are thought to have absorbed nutrients from the water around them. And like most Ediacaran life forms, they disappeared from the fossil record at the beginning of the Cambrian period 540 million years ago, making it difficult for scientists to link them to any modern life forms.
Researchers have previously determined that these early animals reproduced asexually, by sending out clones via stolons or runners, like modern strawberry plants. In the rich waters of the Ediacaran, they thrived.
Life was pretty nice during the Ediacaran, so the need for sex was rather limited. There was relatively little competition, so there was no real pressure to change anything.
Dr Emily Mitchell, lead author
Department of Zoology
Cambridge University
Cambridge UK.
Mitchell and her co-author Professor Andrea Manica used a combination of laser scanning, spatial analysis and artificial intelligence to study fossils from Mistaken Point in Newfoundland, one of the world’s richest sources of fossils from the Ediacaran, to help determine why early animal evolution slowed down, and why it might have sped up again.
The researchers first showed that asexual, stolon-based reproduction limited competition, then built a computer model to simulate how early animal communities might behave under different reproductive strategies. They ran the model thousands of times while a simple neural network helped narrow down which simulations best matched the diversity patterns seen in the fossil record. This approach, known as Approximate Bayesian Computation, allowed the researchers to work backwards from the real data to estimate how far organisms spread and how strongly they competed for resources.
Using this method, the researchers showed that limited dispersal linked to asexual, runner-based reproduction could explain why early animal communities had relatively few species, and why a later shift toward wider dispersal and sexual reproduction coincided with a sudden burst of evolutionary diversity.
Competition and stress have been prime drivers of evolution for billions of years, but in the deep waters of the Ediacaran, asexual reproduction meant that competition was limited.
If you’re connected to your neighbour by these runners, then you’re sharing nutrients and you don’t need to compete with them.
Professor Andrea Manica, co-author.
Department of Zoology
Cambridge University
Cambridge UK.
However, as life in the Ediacaran slowly spread from the deep ocean to shallower waters, early animals faced more pressures: tides, storms, changing temperatures and nutrient levels all would have made life more precarious, leading to increased competition for resources.
If you’re suddenly in an environment where you’re essentially getting killed a couple of times per year, then that changes everything. Stress essentially leads to sexual reproduction, and when that happens, we can see a massive increase in dispersal distances as animals attempt to colonise new areas due to an increase in competition.
Dr Emily Mitchell.
As these early animals adapted to both a new mode of reproduction and new habitats, there was a corresponding increase in diversification, leading to the Ediacaran ‘second wave’ of animal evolution, a process that accelerated further in the Cambrian once animals became mobile. Publication:
So the creationist "first man waiting for the first woman" question is not an argument against evolution; it is an argument against ignorant stupidity; a crude parody of evolution that no evolutionary biologist believes. There was no first man waiting for a first woman. There were ancestral populations in which inherited reproductive mechanisms changed gradually, and in which genetic mixing gave some lineages an advantage over purely clonal reproduction. The new Cambridge study shows why that mattered: once reproduction allowed genes to be reshuffled and lineages to disperse more widely, evolutionary diversity could accelerate.
Once again, we see the gulf between creationist rhetoric and scientific reality. The creationist caricature imagines evolution as a sequence of impossible miracles: a first man appearing alone, waiting hopefully for a first woman to evolve from nowhere. Science, by contrast, deals with populations, ancestry, inheritance, variation, selection and deep time. It explains why there never needed to be a first male and first female, only ancestral populations in which reproductive strategies changed gradually.
The Cambridge study adds an especially interesting dimension to that picture because it shows how reproductive mode could have affected the pace of early animal evolution. Asexual reproduction may have served the Ediacaran organisms well enough in stable conditions, but it also limited the genetic mixing and ecological competition that later helped drive diversification. When sex became more widespread, evolution had more combinations to work with, and natural selection could assemble successful traits more efficiently.
This is not a problem for evolution; it is evidence of evolution. It is exactly the sort of thing we should expect if life diversified through natural processes acting over hundreds of millions of years. It is also exactly the sort of thing we should not expect if all organisms were created as fixed kinds a few thousand years ago.
Creationism has no mechanism, no predictive model and no serious explanation for this pattern. It offers only a childish parody of evolution, then mistakes its own parody for an argument. The fossil record, population genetics and comparative biology all tell the same story: sex did not begin with a lonely man waiting for a woman. It evolved because, in changing environments, genetic mixing gave populations an advantage. Once again, the evidence does not merely fail to support creationism; it exposes how little creationism has to say.
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