The Flood Bottleneck

One of the common arguments presented in an effort to challenge the Biblical model of origins is the impossibility of a flood bottleneck. The argument is that were humans and animals cut down to a tiny population size (two for humans and many animals, fourteen for other animals, unknown low numbers for sea creatures and plants), then the animals should have gone extinct. However, this argument is specious for a couple of reasons, that we will examine today.

The Bible gives us a clear account of the land-dwelling, air-breathing animals’ survival. Clean animals came in sevens, unclean animals in pairs. In the terms of population genetics, this is termed a bottleneck. A bottleneck is any sharp drop in population size, which is often associated with a roughly equivalent loss in genetic diversity. According to the evolutionists, this catastrophic drop in genetic diversity should cause all of life to go extinct, or, at minimum, have basically no genetic diversity. . But does it actually work that way? Turns out, the answer is no.

When a bottleneck happens, as it did in the flood narrative, the population drastically shrinks, then eventually starts growing again. How long the bottleneck lasts varies depending on the event. In the case of the Flood, it was one generation. That is a very important factor because of what happens in a bottleneck. In population genetics, there is a concept called genetic drift. According to genetic drift, alleles will tend to drift to fixation or out of the population based on their frequency. For example, if an allele is present in seventy percent of the population, it has a seventy percent likelihood of drifting to fixation in the population, provided that the population is not experiencing selection. This is very important because drifting to fixation takes time. In fact, depending on allele frequencies, and the random rolling of the dice that takes place during recombination and reproduction, it may be dozens of generations before fixation occurs.

The length of time it takes for fixation to occur matters because it impacts the flood bottleneck. The flood bottleneck was a single generation. While some alleles might have been lost, particularly in organisms that have longer generation times, most alleles would have been passed on to the offspring. Fixation would have occurred largely as a result of selection as organisms moved away from the Ark’s landing site. Genetic drift would have played little role in the immediate post-flood period, as populations were mobile and interbreeding, causing new alleles to fluctuate in and out of populations. A short bottleneck is not a problem at all for the creationist position.

However, the evolutionists do have a bottleneck problem of their own. According to the evolutionary out of Africa model of human origins, humanity originated in east Africa and maintained a small (10,000 odd people) population size for thousands of years. There is a significant problem with that hypothesis. First, in terms of a bottleneck, this would drastically reduce genetic diversity simply due to genetic drift. Thousands of years is more than enough time for alleles to drift to fixation in a fixed population size, which is what the out of Africa model proposes.

It actually gets worse for the out of Africa model. We can draw an analogy to cheetahs, which have a population of roughly 10,000 today. Conservationists are very worried about cheetahs. They are having smaller litters and becoming less fertile over time. In other words, they are genetically falling apart. And they have much shorter generation times, and larger families than humans. This creates a giant problem. If humans sat at a stable ten thousand person population for thousands of years, it would be very easy for deleterious mutations to spread in the population and not drift out. This would cause the population to do what the cheetahs are doing: implode. Yet evolutionists argue that out of this lengthy bottleneck arose modern humans. The statistics simply do not match with what the evolutionists are proposing.

As we have seen in this, albeit very short explanation of bottlenecks, short bottlenecks, like the flood bottleneck, are not bad for a population long-term. However, long-term bottlenecks like those afflicting the out of Africa model are very harmful to a population. Deleterious mutations build up in the population and eventually cause it to go extinct if a bottleneck extends more than a few generations. However, since the flood bottleneck was a single generation, it did not have any of these deleterious effects. As always, the Biblical model fits the evidence much better than any other model.

Do you know what’s going to happen when you die? Are you completely sure? If you aren’t, please read this or listen to this. You can know where you will spend eternity. If you have questions, please feel free to contact us, we’d love to talk to you.

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