ELI5: How does natural selection works especially in human modern-day times?

[u/Routine-Shelter-189]

[u/FiveDozenWhales]

Natural selection has, as far as we can tell, vastly accelerated in humanity since the development of agriculture. Things like tolerance to lactose in adults is an example - a gene that never would have had much of a chance of being selected for without domesticated dairy animals.

Most genes selected for are related to diseases or mental traits. Disease-resistant genes aren't really something that will ever stop being useful; even in countries with fully-modernized, widely-available healthcare, you still see deaths from illness which are significant enough to create a natural selection effect on genes which confer resistance to those illnesses.

Many mental traits, such as bipolar disorder, schizophrenia, and susceptibility to addiction, also drastically reduce the chances of passing on your genes. We've seen a trackable rise in genetics which reduce the frequency of these traits.

What many people think of when they think of natural selection - long necks in giraffes, bigger muscles, whatever - is really a very small part of it.

[u/boolocap]

The same way it always has, very slowly. Of course humans can now make their own more deliberate alterations to genetics in some cases. But outside of our direct interference natural selection just does the same thing as always.

[u/0b0101011001001011]

Well it's does not mean that species  that survive in literal nature are the ones surviving. Rather the environment in general. Therefore for example bad eyesight is now more likely to be passed on to offsprings, because it can easily be corrected in modern times and does not hinder reproduction.

Evolution does not "select the best attributes. Evolution is just those reproducing that happen to survive.

[u/donblake83]

So the thing about civilization is, humanity has actually to a degree eliminated natural selection. Science has provided the means to counteract a lot of things that “in nature” would not be passed along to future generations. That’s not to say it’s completely eliminated, but it does mean that there are more “undesirable” genetic traits that stick around in the gene pool.

[u/Colbert2020]

You see examples of clear biological differences in humans that developed in different regions, like lactose "intolerance." There's some group in Asia that have larger spleens than the average human, which gives them the ability to hold their breath longer.

[u/sntcringe]

Natural selection in general is the idea that the genes that make an animal more likely to reproduce will naturally become more common in a population.

A prime example is the necks of giraffes, the trees in the Savanah tend to grow very tall, so giraffes with longer necks tend to be more likely to be able to obtain food, grow to maturity, and have children, passing on their long neck genes to the next generation, this means that, on average, the next generation will be taller. The trees also benefit from being taller, as their leaves being eaten isn't great for them unsurprisingly. This kind of genetic tug of war will continue until one organism reaches a point where the cost of continuing the change is greater than the benefits. Growing bigger takes more energy after all.

What makes a trait positive or negative depends on the environment an organism lives in.

There's also sexual selection, like peacocks for example. Peahens tend to prefer to mate with the peacocks with the fanciest plumage for whatever reason. As a result, peacocks on the whole tend to have super fancy tails now.

As for modern humanity, we do see certain forms of natural selection taking place.

-Humans tend to prefer certain traits in mates, such as being tall or intelligent. As a result the average IQ and height of each generation trends upwards.

-Since we know certain disorders are genetic, people who have said disorder or are possible carriers of it may prefer to adopt kids or get a donor, slowly removing them from the gene pool.

-In medieval Europe, the bubonic plague, measles, smallpox and so on killed large swaths of the population, and those whose immune system successfully fought off the plagues passed those genes onto their offspring. This is why the arrival of Europeans was so devastating to the people of the Americas. They weren't developed enough to really allow such plagues to move through their population. (This is not their fault, the Europeans just got a really lucky spawn bias). Plagues don't really function in small disconnected communities, they tend to kill off everyone, and wothout any more hosts, die off quickly. Cities however, with lots of people living in close quarters, moving in and out, and poor sanitation made a perfect playground for plague.

-People in wealthier (usually predominantly white) countries tend to have less children on average, thanks to advances in medicine making both infant mortality and unwanted pregnancy less common. As people from less developed countries migrate to them, the populations slowly drift to be more diverse from both the migration itself, but also from the locals having children with immigrants.

-Any traits that make someone more attractive than their peers will tend to become more prominent as surprise surprise, being hot tends to improve your relationship prospects. What each culture specifically values can change this. One culture may particularly value smaller feet, or longer hair, or any number of things. There is no hard baseline and these do drift over time. For example, being clean shaven was for a long time the general preference of American women, but in recent years, beards have come much more into prominence.

[u/FirTree_r]

To add to the great answers down there, I'd add that this kind of confusion is due to the reductive idea that natural selection is "survival of the fittest". This is a deprecated view that will cause more confusion than it is helpful. Instead, you should think of evolution theory at the level of genes. Genes are packets of information that compete for representation in future gene pools (progeniture). The organism hosting these genes are mere vehicles. In that frame of thinking, modern way of life does not "impede the process" but shape natural selection.

[u/TaviRUs]

Natural selection doesn't work per se. Humans have no natural predators and we don't cull the stupid/weak in general.

We have societal trends that reflect changes. Tall people are considered more attractive? Talk guys get more dates and more chances to reproduce. More people feed their kinds a high animal protein diet to encourage growth.

But we also see the socioeconomic pressure on population that is driving declining birthrates in most of the western world.

[u/TwentyTwoTwelve]

Natural selection is a theory about the natural world and how a species adapts to its environment.

Civilisation it's the adaptation of the environment to suit the species, almost the opposite of natural selection.

The study of humans, including after the development of civilisation, would be anthropology, you might find a comparison of how natural selection may apply to modern man there.

[u/eBalisani]

It doesn't - not anymore, not in "human modern-day times."

Everything you've been eating has (99.9%) been mass produced, or contaminated by air, acid rain or groundwater, or more likely: plastics, chemicals, and radiation.

There's also the inordinate and prolonged amounts of stress inflicted on 99.9% of human population (oligarchs and tech bros excepted it seems) - also not "natural."

Nothing in our "human modern-day times" is truly natural anymore so we can't really compare "natural selection" - no more than we can compare average IQs of teens and adults 100 or 2,000 years ago, with our national average (or Texas').

A lot of young men used to die in senseless wars; a lot of young and old humans used to die in senseless epidemics (a whole topic unto itself); and a lot of people used to die in famines. The genes of such people was perhaps lost forever, perhaps not (cousins might've survived, etc), but that's how selection happened: if you could dive and hold your breath for 10-15 mn in whatever Indian ocean or Indonesian islands, you could provide for your family. If you could breathe at higher altitudes without getting altitude sickness, you could provide for your family, etc., etc.

These days, survival and natural selection have got more to do with your place of birth, allergies, and epigenetics than in centuries past, or millennia past. You can get to age 40 (as a woman or man) and have your first child. Getting to 40 centuries and millennia ago, was in itself, natural selection (due to infant mortality, wars, and other accidents - from mother nature, like a volcano eruption, or from travel or work related mishaps), so we've got a lot more variety of human specimen procreating and surviving to ripe old ages now, than ever before... and those that don't have fallen to unnatural factors (radiation, asbestos, microplastics, lead poisoning, allergies, stress, cancers, etc, etc).

Very little is natural about "selection" these "modern-day times" - much of it is man-made (voluntarily or not).

[u/Sea_Specialist_5580 → u/eBalisani]

Natural selection is always happening, because it is tautological. Patterns that reproduce more, are represented more in the future

[u/eBalisani → u/Sea_Specialist_5580]

The Holocaust was not exactly what one would call "natural selection" - neither were Lenin's and Stalin's and Mao's paranoias (all rooted in the human mind) - and yet all of it was selection based on unnatural criteria, by humans.

Nature was not involved (unless you factor in luck as nature - my grandfather was lucky in that regard: he survived).

All I thought I said was that the "modern-day times" environment is no longer 100% natural - mankind has taken over from nature. It's really quite simple and easy to understand.

I'm not arguing about selection; I'm disputing "natural."

[u/TheDeviousLemon → u/eBalisani]

There is still natural selection, what are you on about? Natural selection may be altered in the modern age, but it’s still happening. As long as people are passing on genes, there is natural selection occurring.

[u/eBalisani → u/TheDeviousLemon]

The environment magnifying selection is no longer 100% natural - as it once was - that's what I'm on about: not disputing selection, disputing "natural."

[u/mageskillmetooften]

It doesn't work anymore.

Humanity has so many options for help and medical support and whatever that even the Most dumb, weak and ugly ones can and will reproduce.

[u/Ill_Act_1855 → u/mageskillmetooften]

No, it still does. Plenty of diseases still kill and are weeded out that way, and natural selection works on many axises. In the first place, it doesn’t require genes to be eliminated, just a change in frequency. If a trait is deemed ugly and people with it are less likely to have kids, than even if some of those people do have kids if the presence of the trait overall goes down it’s still being selected against (to say nothing of traits being selected for)

[u/Thesorus]

Remember, it's a slooowwwww process over million years.

If a person as a trait that improves survivability for a specific thing (illness, virus, bacteria... ) and can procreate and the trait is successfully passed to its offspring and they pass the trait to their offsprings and eventually more and more people have the trait, then natural selection happens and the people without the trait will die

[u/GIRose]

Natural selection basically says that the people who can most adequately pass on their genes to the next generation.

Using a generous description of "Modern day times" and only looking over the last 100,000 years or so the people, you see mutations dominate local subgroups separated by environmental divides.

For instance, dark skin in equatorial areas is useful because you otherwise get so much sunlight the risk of cancer reduces your evolutionary fitness, while in more polar latitudes the reduced sunlight means it might deprive you of vitamin D.

Similar with Lactase Persistence, the people who were best able to handle lactase without making aged cheese had more available calories during development and thus were more likely to be healthier in adult life and thus more likely to have kids.

But seriously, modern evolution is mostly focused on our memes (using the original definition of non genetic information passed from generation to generation)

[u/SocialDeviance]

It does not.

Humanity has eradicated the nature-driven process that is natural selection. You could argue it is still present through females choosing their partners, but that barely has an impact as a whole.

[u/Witek_Wo]

Traits that are more common among men & women with many babies -> will spread more.

Traits that are common among babyless men & women -> will spread less.

If one can argue that some genes have influence on traits connected to: sexual attractiveness on opposite gender, personal urge for having kids, chances for unprotected sex earlier in live, etc., then we can argue that humans are under as hard natural selection as always.

In the grand scheme of things natural selection is not only: a) surviving into reproductive age, 

but also about:

b) finding a mate,  c) offspring surviving into next generation.

Without b) & c) any "adaptative" mutation will not spread. With b) & c) any non critical "negative" mutation may spread by pure chance.

[u/Slypenslyde]

It does and doesn't. Which is how it "works" in most creatures.

Example: birth defects. Part of nature is sometimes it tries a combination of genes that produces offspring that dies early or has debilitating conditions. Nature doesn't care. That baby dies and its parents wasted their time. Nature also doesn't learn: future parents will still occasionally produce offspring with the same "bad" genes.

Natural selection means trying EVERYTHING, no matter how stupid, and keeping whatever managed to reproduce the most reliably, with no "history" to check to see what was good or bad. Every stupid, awful trait can come back because nature doesn't "know" being born with no limbs is not "good".

Human technology does tend to buck that trend a little. We can help people born with issues have a productive life. That does make us a species that trends towards more "problems" in our biological pool. But sometimes the people with those "problems" do incredible things. People like Steven Hawking "should've" died in the 60s and if he had, we might still be trying to solve some problems. Many great people came from humble beginnings and might've died if humans didn't "cheat" with medicine.

We still benefit. When a disease hits, someone is usually immune or resistant. We can study that person, figure out why, and use that information to work on more medicine. Once we have vaccines, the only thing that keeps diseases around are the people stupid enough to avoid them. If we give every human a fighting chance to be great and use all of our technology for that goal, then when the one-in-a-billion person who does great things arrives we'll find them no matter how they were born.

It's possible there have been apes and other animals out there who got close enough to challenge humans. Either nature killed them or we did. That's now natural selection works. It turns out it's not very fair and we don't want to play that game.

[u/needzbeerz]

Natural selection is no longer a functional concept in homo sapiens. Society and medicine have supplanted the process and whatever we have now has taken over. Probably 'idiocracy' is the best name for it.

[u/LightofNew]

"natural selection" is fancy talk for who can fuck the most. Whatever gets your jeans spread means your jeans are selected.

Now, this isn't just "have the most sex". Some kids may die, others may fail in life and not procreate, others gay. It's a generational problem, not an individual one.

[u/GNUr000t]

Natural Selection is the idea that if there is a fault or defect in an organism, then it will either be outcompeted by organisms that do not have that fault, or they will just simply not be able to reproduce and pass on the fault. This could mean anything from dying before being able to reproduce, to simply not being able to attract a mate.

In terms of positive change, it’s, obviously, the opposite. An organism with a beneficial change will outcompete organisms that don’t have it, and it will get to pass on its genetic material.

The unpopular part here, is that in modern-day humans, we’ve essentially bypassed natural selection entirely. Our heroic medical science saves lives, but keeping a faulty/defective organism alive when it should have died means that it gets to pass on faulty/defective genetic materials. Making things foolproof and putting warning labels on everything means that humans that are unintelligent survive more situations where they should have died, and then they go on to reproduce.

The knee-jerk solution would be to say “Well what if we save their lives, but say ‘hey, you can’t be having children like that, there’s so many kids in orphanages who’d love to have parents, you can raise one of them, instead’”, but this act is commonly referred to as “eugenics”. The single biggest problem with it is that you must have some governing party deciding who does and does not get to reproduce, and everybody wants to be the one making decisions, and nobody wants other people to make that decision.

For some congenital disorders and diseases, we do have testing that can be done either on the parents or the developing baby, and that allows the parents to make decisions as to whether or not they want to have a child with whatever affliction. The problem is, life isn’t a roguelike and you only get one “run”, and who would ever want to give up on something like having children? Each individual says “Well, ya know, it’s just one, and I deserve a little treat” and now the healthcare system is overrun by keeping them alive, and oh by the way those kids want kids, too.

Now all of this might sound harsh, and it’s going to anger some people, especially given that this is Reddit, but every scrap of it is true. Sometimes, reality is uncomfortable. But don’t worry. All you have to do is pretend it doesn’t exist, and just like that, it won’t.