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iayork t1_jdqwpp2 wrote

TL;DR: rapidly expanding populations have faster adaptive evolution, and that’s what is seen in humans.

> Human populations have increased vastly in numbers during the past 50,000 years or more (1). In theory, more people means more new adaptive mutations (2). Hence, human population growth should have increased in the rate of adaptive substitutions: an acceleration of new positively selected alleles. … In such a transient, large population, size increases the rate and effectiveness of adaptive responses. For example, natural insect populations often produce effective monogenic resistance to pesticides, whereas small laboratory populations under similar selection develop less effective polygenic adaptations (5). Chemostat experiments on Escherichia coli show a continued response to selection (6), with continuous and repeatable responses in large populations but variable and episodic responses in small populations (7). These results are explained by a model in which smaller population size limits the rate of adaptive evolution (8). A population that suddenly increases in size has the potential for rapid adaptive change. The best analogy to recent human evolution may be the rapid evolution of domesticates such as maize (9, 10).

—Recent acceleration of human adaptive evolution

The author of that paper has a blog post giving more background and explanation: Our new paper on why human evolution accelerated. His summary there:

> Our evolution has recently accelerated by around 100-fold. And that's exactly what we would expect from the enormous growth of our population.

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TheReapingFields t1_jdqmsv4 wrote

Well, on the one hand that means an expanded gene pool, and that is great, because generally this means greater potential for adaptation, and a lower risk of total species loss due to an over concentrated gene pool.

On the other hand, resources only diminish as time wears on, and people need those. The more people, the more resources are needed, the faster those resources get used up, the harder it becomes to locate required resources... Theres a whole doom spiral associated with that.

Then there is the environment itself, which, if current scientific consensus is something you care about, seems to point toward the human race being the biggest threat to itself or its habitat, although the threat we pose COULD be diminished, without diminishing our numbers. It would only require the end of for profit energy generation, end the use of combustibles as fuel for energy generation, massive advances in fusion technology, renewables and other things that don't get the funding they need because of politics and financial cartel operations.

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BallumBallum t1_jdr967o wrote

Well idk about humans but for bacterias after exponential growth rate there is a plateau and then a collapse because there is no more nutrients.

My guess is we are no better than bacterias and we are now at the end of exponential growth and reaching the plateau

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happyhumantorch t1_jdqucmq wrote

In general, a larger population increases the power of natural selection and reduces the rate that alleles lost by random chance. Both of these increase the robustness of a population over time.

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Clearchus76 t1_jdsmrvs wrote

I feel like we are about to find out. We are a global economy that is about to become regional and a lot of people are going to starve. Africa is going to be in a very bad place soon and if China doesn’t pivot into something else soon they are going to be in a bad place as well.

So we will have to evaluate what is left over in the coming decades.

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Busy_Passage5400 t1_je7uq1x wrote

This is wrong, if as you claim the global economy is about to become regional, then third world countries with their large amounts of self-sufficient subsistence populations are the best placed to ride it out. Also the net drain of resources from Africa to Europe and American would stop, which would be a further boost

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Intrepid_Pitch_3320 t1_je4w7gy wrote

typically in nature a population explosion event occurs when top-down forces, predation, go away for some reason, like parvovirus in wolves (or extirpation by humans) can result in moose, deer, or caribou population explosion. Invariably, bottom-up forces will then kick in like sickness and starvation. The whole ecosystem takes a big hit in indirect ways. Humans have staved this off to some degree by our technological abilities to feed and heal ourselves. At the expense of many other species of course. But make no mistake. Things are getting worse. We can run, but we can't hide from it. Cheers.

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OvershootDieOff t1_jdqqojo wrote

Lack of selection means many unfit genes propagate where harsher environmental conditions would have resulted in their demise. Genetically the benefits of rapid population growth are a larger gene pool from which future generations could draw to endure something like a pandemic that removes a large fraction of population.

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atomfullerene t1_jdrdhbn wrote

>Lack of selection

This is a common misconception. People think natural selection works like this: Individuals which don't survive to reproduce are selected against, and individual which do survive to reproduce are selected for.

In that case, you would expect an expanding population to be experiencing little selection, because most individuals are surviving to reproduce, right?

But it's not correct, because what natural selection actually selects for is individuals who reproduce the most. There aren't just two buckets, where an organism is either in or out. If a trait results in the production of, say, 10% more offspring on average, selection will favor it.

In a growing population, traits which enhance reproduction on average will spread, and that's natural selection. And it will happen more efficiently too. In small populations, natural selection is countered by drift. Basically, a trait that's beneficial might not be selected for, because the individuals who have that trait might happen not to survive for some other reason. Chance might just be against them. But a big population reduces the effect of chance (and therefore drift) for the same reason that it's much easier to roll a 1 on one dice than on ten dice all at the same time. And as you note, a larger gene pool also means more variation to draw potentially beneficial mutations from in the first place.

> means many unfit genes propagate

Also, "unfit" genes don't exactly propagate in the absence of selection. Take a gene for something (say, a medical condition) that was previously harmful, and remove all selection on it (properly speaking this means the gene isn't unfit anymore, but we'll disregard that because I know what you mean). This won't actually cause the gene to propagate, instead it's expected to remain at the same frequency in the population. To actually spread, there would have to be some active benefit of having the version of the gene which (formerly) caused the disease. You could in theory have a slow growth of gene frequency due to mutations, but this is a slooooow process.

And remember, if the medical treatment allows people with the gene to survive, but they still have reduced fertility or are otherwise less likely to have kids than the average person, that gene will still be selected against.

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huckerbjk t1_jdqwcz0 wrote

Peanut allergies, Autism , heart disease, etc increase when conditions allow recessive traits to exist or even flourish because of abundance of resources to deal with those traits/ diseases

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Ok_Construction5119 t1_jdsirpc wrote

Heart disease rarely kills you before you have the chance to reproduce. That's why our teeth are only built to last 40 years or so

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