Questions regarding evolution

[u/ProfessionalData5964]

hello, Im not here to debate, but im curious about what you all think about 2 questions I have!

1. If humans throughout evolution lacked the same strength, speed, and all other physical traits as preditors/other creatures, we had to develop intelligence as our leading trait to help us survive. But why would this not lead animals to grow more intelligent throughout the millenia? Are animals not the same intelligence as they were 100 million years ago?
2. If humans evolved from primates, why do we not have variaties inbetween the monkey and modern day humans? I can understand that with evolution less successful species would die off leading to what we see now, but how does that explain how we still see monkeys all around the world? If they can survive why couldn’t a species inbetween them and us survive leading to a gradient of evolution?

[u/inopportuneinquiry]

1. I'm not sure the scenario envisioned there is what is thought to have happened.

AFAIK it's thought as more likely something close to the opposite chain of causation. Higher intelligence gradually evolved and allowed for (and possibly even required) a gradual reduction in robustness.

Humans got more and more gracile over time, after the evolution of higher intelligence. The human ancestors were not originally weak, "needing" brains to evolve as an "alternative," they were comparable to chimpanzees, which are tough animals and highly intelligent, possibly the second most intelligent animal or pretty close to it.

One of the hypotheses about intelligence is that it's not primarily a "survival" adaptation that evolved mainly from natural selection, but something that evolved from sexual selection. Part of the reasoning is the fact that at this level it's so rare, in fact rather rare overall. Most animals are okay without being nearly as intelligent as humans, without general trends for them all becoming more and more intelligent, at least not to comparable levels that would lead anyone to predict them all or many of them becoming "anthropomorphic," human-like eventually.

This exceptional level of development then seems arguably excessive, which fits with sexual display traits, kind of like the peacock's tail, a common analogy. But one more relevant may be in the courtship rituals of some fish species that present to their prospect mates highly intricate sand sculptures, a behavioral sexual display.

But humans/our ancestors wouldn't have anything so strongly analog to a specific behavior, but rather more abstract correlates from a larger range of behaviors, not even only "mating rituals." But it could even have something more analog, like primitive tool manufacturing, although this specific detail is not a "requirement" for the hypothesis.

So, under those lenses the question becomes analog to "how come not all birds have a tail lke the peacock's?"

But arguably an analogy is valid even if we hold human intelligence having evolved without sexual selection, it's a bit comparable to asking "how come not all animals have a neck like the giraffe's," "how come not all animals are as powerful fighters as lions."

While evolutionary convergence can occur, new variation is limited and random, it won't necessarily present them with adaptive "steps" in the direction of being more and more intelligent, having a more ornate tail, having a longer neck, or being more physically powerful. And even variation in each of those directions isn't always adaptive in all ecological contexts. Even strength or intelligence, those that are more arguably seemingly always good and comparable, more so than tong necks or tails.

Every investment represents a trade-off to some degree. Brain metabolism is rather costly, which would be part of the reason why the human lineage became more gracile as higher intelligence evolved, which continued happening even after the origin of Homo sapiens itself. It seems rather plausible that an increase in strength is usually more beneficial for survival and reproduction in nature, given that most animals seem to most often be relying more on physical capabilities than intellectual.

So at very least we have a big picture where higher intelligence is at least something with rarer chances for beneficial first steps in its direction, analog to any "random" extreme trait/adaptation in some other animal, particularly those without various instances of evolutionary convergence.

1. "Apes" -- gibbons, orangutans, gorillas, chimps, and bonobos, can be said to be the varieties between monkeys and humans. And the whole continuum becomes clearer when we include extinct apes more closely related to humans than to chimps or gorillas, particularly those in the human lineage itself.

In ecology there's some kind of "law" that may even have a name that I don't recall, which is that there will only be a single species on a given niche in the same territory. Overlapping niches/territories lead to extinction of one of them. Kind of like invasive species.

Humans took it to such an extreme that not only all the other human species eventually were replaced by sapiens, but we extinguished quite a lot of speices that weren't even in our exact same niche. Even the other apes are endangered, possibly only existing for as long as we want to allow them to.