Before anyone comes for me, I grew up southern baptist – went to a private christian school & was homeschooled for a few years. The extent of my “science” education when it came to evolution & the origin of the universe was “if we came from monkeys why do monkeys still exist?” and “look at this galaxy that’s shaped like a cross, isn’t god amazing!!” I’m an atheist now and would like to have some sort of understanding of how our world came to be, but trying to figure it out as an adult with no real foundation has been incredibly difficult, and none of it’s making sense. I also know I’m asking a lot as all 3 of those subjects are pretty extensive, so if you know any good videos or books I’d love some recommendations!
In: Biology
Given how each topic could fill in a timeslot or three, I’ll just focus on evolution.
All life^1 is centered around the DNA which acts as a “blueprint” for the organism, and it contains all of the information required for the organism to function. DNA is why identical twins look physically the same because the “nature” side of “nature vs. nurture” is identical.
Bits of DNA can be grouped into units called genes. The layman definition for that is that it’s a part of your DNA that “does one thing,” so a gene might define how hail follicles grow, or how much growth hormone is produced during adolescence, and so forth^(2).
The process of passing these genes on to your offspring is not perfect, so sometimes the genes are damaged. Maybe they’re copied incorrectly, or maybe the father spent too much time in a poorly ventilated basement which led to a stray ray of radiation from radon gas to damage the DNA. Mutations happen entirely at random because of this, and most of them are irrelevant. Not all of your DNA is useful, so damaging a part of it might not change anything at all. Sometimes, something very important breaks, so the clump of cells never even develops into something the mother notices because it’s that unviable. But sometimes a gene mutates in such a way that it can be useful. It’s very rare (after all, it’s much easier to break something than to repair it) but in that case, the mutation provides an advantage. If a trait is harmful or beneficial, that causes **evolutionary pressure**. If the trait is bad, then the offspring is statistically more likely to die out, so the genes spread less. Conversely, if the trait is positive, then the genes are more likely to spread throughout the population.
Dogs are a good example of this. In the wild, a friendly wolf with a muted survival instinct would die off pretty quickly and take those traits with it, but if that happens to, say, an abandoned wolf cub which is picked up by a tribe of humans, it can become an enormously favored trait because humans love to pack bond. Humans can artificially^(3) select for these traits, so over thousands and thousands of years, when humans always bond most with the friendliest and most cooperative wolves, eventually you have something that is so different from a wolf that we call it a dog. A part of it is unintentional (a man might just dislike and reject a dog that is aggressive and bites him, leaving it to find its own food) but we can also selectively breed for specific traits which is how we’ve specialized wolves into everything from lap-dogs to shepherds, service dogs or [turnspit-turners](https://en.wikipedia.org/wiki/Turnspit_dog).
This is how **microevolution** works, i.e. how different traits appear and spread within a species. A dog is born with an abnormally expressive face, and because that makes it easier for humans to communicate with it, it becomes a beloved dog and the trait gets passed on as much as possible.^(4) Because of how strongly humans can influence which genes are passed on and which aren’t (which removes a lot of the randomness from the kind of evolution that happens in nature: even the fastest, smartest, most genius wolf might lose to its mangy brother in a competition on a bad day) the variety of dogs you see is staggering.
**The imporant part here is that it is all, ultimately, just statistics**, and evolution has no overarching goal to it. Humans can use it for their own purposes as mentioned above, but evolution itself is a blind and deaf force. If a canine is born with a mutation that makes its brain smaller and less responsive to danger, it will likely die in the wild, so the trait is unlikely to spread. If that mutation happens to a dog, then it might not matter one whit because humans will keep it alive anyway. Even though to the person reading this, a “smart” dog might seem better than a “dumb” one, evolution neither cares nor prefers: if it works, it works. If it doesn’t, then it doesn’t, and that’s why modern dogs (literally) have smaller brains than wolves and why many overbred dog breeds have debilitating health issues. Subjectively, it is terrible that a dog has such a malformed skull that it can’t breathe properly, but objectively, if breeders see that trait as “pure” and make the dog have a lot of offspring, the trait will live on.
**Macroevolution** (speciation, in this context) is just microevolution over and over again. This is where many religious sects draw the line (largely because microevolution is so blatantly obvious that it’s embarrassing to attempt to refute it) but there is no real reason why small changes over enormous timescales wouldn’t yield a result that was entirely different from what you started with. The rule of thumb^(5) for defining species is if they can produce fertile offspring together, so if you pile a change after change after change in different directions for two separate populations of a species, eventually they will no longer be compatible.
Modern humans showed up about 300 000 years ago, but saying that we came from monkeys is glossing over some details. Chimps and humans share a common ancestor, but that was some ten million years ago, which was effectively just a primitive and weird-looking monkey. Two groups of these creatures got separated at some point just by chance, and because of different environmental pressures, one group drifted towards what would become modern chimps and the other towards what would become modern humans. The “why are there still monkeys around” argument is fundamentally misunderstanding the process, so it’s like asking “If Estonia seceded from the USSR, why are there still Ukrainians around?” which is silly because one of those nations is long gone and the only thing in common between the remaining two is that both of them have a hot-topic border eastward.
It’s important to note that none of what I’ve written is in any way related to **abiogenesis** or how life was formed. The theory of evolution doesn’t concern itself with where life came from, whether it was from a meteor, a brackish puddle or the Gnostic demiurge going against the emanations to bring forth life. Where life came from is very much an open question, and a very difficult one to answer at that because on Earth it happened over four _billion_ years ago.
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^(1) How you define “life” is subjective, so I’m just focusing on anything that looks like bacteria or bigger.
^(2) How genes actually express themselves is horribly complicated even without getting into epigenetics. It’s rare for one gene to be solely responsible for any one trait, so whether you’re tall or smart or any other thing is usually the result of a complex web of related genes.
^(3) “Artificial” is a loaded term here, really. Any selective pressure is just as valid as another, so friendly pets getting all the care and attention from humans is no different from taller-necked giraffes eating better or faster gazelles outrunning predators.
^(4) Dogs have significantly more expressive facial muscles than wolves do. It’s even in the whites of their eyes: eye contact is important for humans, so dogs which can indicate which way they’re looking work better with humans.
^(5) Again, real life is complicated and doesn’t fall into neat buckets, so you always have edge cases which buck the trend, but unless you’re a specialized biologist, the rule of thumb is just fine.
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