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lainchan archive - /sci/ - 122

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I have a question about evolution. I'm not a creationist or anything like that so do keep the bullsoykaf away, it's just a genuine question.

As far as i understand evolution works by trial and error, i have a race of X and after some generations a mutated X is born with a distinct characteristic, this characteristic might allow mutated X to live longer, have more partners and/or just be more successful in living and thriving, thus he reproduces more and perpetuates his mutation in his race.

My question is about the nature of this mutation. If i'm able to see better at night that's a perfectly reasonable and random-looking mutation, but if i'm able to detect the specific characteristics of rotting food, what the fuarrrk is going on? Between all possible evolution paths i could possibly take, i somehow become able to detect the specific type of bacteria living inside rotten food, and not only that but i can also smell rotten food and recognize the fact that what i'm feeling when i eat rotten food is something bad and i should stop. And even if i do eat, my digestive system will say nuh uh bitch boy you throwing that soykaf up. This boggles my mind, food might be a bad example since we so badly need it to survive, but we can use other animals and the strangely synchronized characteristics will show up, that classic example of the moth is one of them, the moth that changed colors to adapt to the urban environment, adapting to the exact color in a change of environment doesn't look very random, specially considering such a low period of time.

So what's going on here? This really feels like one of those incomplete explanations that high school teachers give you do not overload you with unnecessary complexity, however i never got a better explanation for how evolution works and how much of it is just dumb luck.


You pretty much have it right. All of these things come about just fine as the result of random mutation and selection.

>i somehow become able to detect the specific type of bacteria living inside rotten food

Bacteria has always been part of our environment. It's no more unreasonable that you'd evolve to dislike the smell of bacteria that evolving to dislike the smell of anything that's dangerous to us. The bacteria is also evolving in the same way but with us as it's environment (so as we evolved livers bacteria evolved to live in livers etc). We can see the same sort of thing all over. In symbiotic, parasitic and predator-prey relationships, each will have evolved alongside the other. It's because of this that ecosystems can be so fragile.

>the moth that changed colors to adapt to the urban environment

Evolution can suddenly go very quickly in the face of changing environments. Prior to urbanisation there will have been a handful of moths that mutated to be grey every generation then got eaten for standing out so much. Post-urbanisation instead of dying off quickly they became a large portion of the moths that didn't die off. Obviously this will have taken a few generations with a lot of randomness in which moths survived but moths have very short life spans. We can see the same thing happening with bacteria and antibiotics. It doesn't matter if 1 bacteria among the millions in a person mutates a resistance, that bacteria will be the only one to survive.


>you'd evolve to dislike the smell of bacteria that evolving to dislike the smell of anything that's dangerous to us
Or rather people that didn't have that trait were more likely to die from food poisoning and only the ones that did are still around. Talking about evolving as an active effort causes all this confusion.



And to add, each selection per generation weighs the total effectiveness of that existence against it's cohorts. That is to say, all genes are selected or deselected at once as the environment tends to be pass/fail. Either you live & thrive or you don't. The thriving part is of course a part of continuum, but the living part, not so much.

SO any single trait in isolation is pretty difficult to weigh in context, since the organism has a plethora of characteristics that generate an emergent effect. Detection of bacteria is in of itself not a single trait. It is informed by smell, cognitive ability, etc.

Simple phenotypes are easy to see and manipulate, but when we delve into complex behavior, that is a different approach altogether (the analysis of the behavior, that is).


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As other lains have said, you got it mostly right.
One small comment tho, every individual born from race X will be 'mutated', there are always random mutations in a generation's genome. In some ways evolution relies on dumb luck, and as you prolly know there are few things crueler that evolution.
Pic related.


To add to what other lainons have said, it's wrong to believe that every aspect of race X have evolved in race X: most characteristics will have emerged from an ancestor/previous races. Knowing this, it's easier to imagine changes happening in some ancestral species (say a zooplancton-like animal) in which discriminating good from bad food becomes a huge evolutionary advantage because one bad meal would kill you. So from that point on, it just becomes a question of not loosing that capacity and refining it to what it has become today by the fact that it's a evolutionary disadvantage to not have it (like >>142 mentioned).


i guess, from what i can gather from your post, it's all about your curiosity of the nature of evolution and the roll of the die of characteristics. how do you end up being able to avoid something instead of having a different characteristic of building up against it? (i.e. sensing rotten food, rather than the characteristic of developing a stomach that can handle rotten food).

if i understand this correctly, i'll try to explain.

evolution is not goal-oriented in the sense you originally thought. it has no agency. mutations are definitely random. but the process of evolution that acts on those mutations is not really.

natural selection (the mechanism of evolution) is often described as survival of the fittest. another way to think of it (that is perhaps a little more accurate) is elimination of the unfit. (fitness in this sense just means the capacity of an organism to reproduce and pass on its genes to subsequent generations.)

random mutation generates genetic diversity. some traits that result from these mutations are adaptive ("useful"). this will allow individuals with those traits to survive to reproduce at higher rates than organisms without those traits. some random mutations generate maladaptive ("bad") traits that do actually are detrimental to an individual's survival. organisms with maladaptive traits therefore don't survive long enough to reproduce. or if they do, it isn't at the same rate as organisms with more adaptive traits.

to continue this example: the creature of the same race both branch off with two characteristics: one has the stomach to deal with rotten food, the other is able to sense what is rotten and avoids it. while the race that can deal with rotten food doesn't exactly die, its body becomes more and more adaptive to that lifestyle, and begins to turn into another creature entirely from it's former race. it starts to thrive and even need the bacteria of that rotten food, versus the original race itself, continues to avoid and evolve in a different way. it's how different species develop, although species can be so closely related its those really distinctive environmental factors that forced those mutations that separates them.

so what traits appear is random. but what traits persist in a population (what is or is not adaptive) is not really random. it is entirely dependent on the environment.

Tl;dr: mutations are random, but natural selection (the mechanism of evolution) is not.


Y'all guys should go watch some david attenborough documentaries. cosmos also explains this stuff pretty well.