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The animal I'm particularly focusing on is a cat, for which I'm curious how long it would take for said cat to evolve into a bipedal, intelligent, humanoid being capable of complex language and all other things that an intelligent species can do, if it's even possible.

The world that my story takes place in is where global warming and climate change aren't necessarily something to worry about, and the planet has plenty of time to change.

The cats are mainly domestic, and a lot of them had owners before all humans left the planet to travel space. After that, they all became wild for however long it takes for them to evolve into humanoid creatures and take over the planet.

I'm not sure if continental drift will affect anything, because again, I'm not sure how long this evolution will take.

So how long would it take? Is it even possible for the cats to evolve, or is it something about their species that prevents it?

If there's anything I need to add to this to make it more clear, let me know.

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    $\begingroup$ It is a misunderstanding of evolutionary theory, however, to see this as a necessary process, and an even greater misunderstanding to see it as one directed to a particular outcome. (OK I copied that entire sentence from somewhere) $\endgroup$ – user6760 Dec 17 '19 at 4:17
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    $\begingroup$ Felines are very highly specialized hypercarnivorans. By comparison, primates (including humans) are relatively unspecialized generalists. (Primates are much closer to the primitive mammalian body plan than felines.) I strongly suggest replacing the starting point with rats; at least rats retain the primitive mammalian hands... Then it's basically a matter of re-doing the original evolutionary path; one hundred million years or so. $\endgroup$ – AlexP Dec 17 '19 at 9:42
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    $\begingroup$ Well to quote Red Dwarf, Lister was in cryo stasis for 3 million years during which time his pregnant cat's decedents had evolved into humanoids, developed a civilization and had left Red Dwarf, leaving only Cat's parents behind. So less than 3 million years :) $\endgroup$ – Riddles Dec 17 '19 at 11:21
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    $\begingroup$ You should read the book Red Dwarf amazon.com/Red-Dwarf-Omnibus-Better-Than/dp/0140174664 The character Cat evolves from a pet cat because it's on board a human-constructed space ship without any humans, and everything is designed for humans. $\endgroup$ – puppetsock Dec 17 '19 at 13:31
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    $\begingroup$ 0 years. Because let's face it, once we master genetic engineering someone's going to create a cat girl. $\endgroup$ – Hink Dec 17 '19 at 15:18
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It's highly unlikely that a highly specialized form like a feline develops into another highly specialized form like a humanoid. Too much rebuild to be practical.

Evolution usually works better starting from a general purpose form and ending up in a specialized one, as it is easier to select the advantageous traits.

If a feline is specialized in hunting, losing any of the related character (i.e. the claws) in the transition to humanoid would be disadvantageous and would lead to a dead end.

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100,000 years (or 100,000 generations), give or take, assuming ideal conditions

So, let's get the math out of the way first; the first animals of the human genus appeared on earth around 2.5 million years ago. Assuming that we are relatively new on the scene, and we are estimated to have first appeared around 100,000 years ago, that would mean that it has taken us around 2.4 million years to evolve from our first ancestors. If we make the math easy on ourselves and assume that a human 'generation' is 24 years, that means that we evolved in 100,000 generations. That assumes of course that the early homonids were almost cat-like in their levels of intelligence and interaction with the environment, which is a large assumption to make.

Cats are capable of gestation within 6 months, but (again to make the math easy) let's assume that the average feline generation is 1 year - if so, and if it takes the same number of generations to achieve humanoid intelligence and traits, we're looking at around 100k years for it to happen.

There are some massive gotchas in that estimate though. First, cats can live for 10 to 20x past their first batch of the next generation, and they remain fertile for a lot of that. There would be a massive cross-fertilisation of 'generations' as a result meaning that cats would be unlikely to have generational progression on the same rate as humans.

Additionally, humans have very few children by comparison, live for only around 3x their age at their first generational production and are fertile for a lot less than that. This is important because it means that there is not as much cross-fertilisation across the generations but even more importantly, less competition for resources between generations. Cats are going to live for some time, constantly cranking out offspring, meaning that there is a high chance of a population blowout that could wipe out the species through stripping of all resources if a given generation proves sufficiently prolific.

Also, cats are already well adapted to their function as hunters, there are few threats that would evolutionarily reward the high expenditure of energy in neural enhancement like what humans were adapting to. Cats are already 'intelligent enough' for what they do and it would take a very specific set of circumstances to make intelligence more important than their existing traits in hunting.

What is far more likely is that cats will run out of food and begin to compete with each other if their numbers increase in an uncontested environment. Intelligence may be a desireable trait that is rewarded with survival in such a case, but it is rare enough that I doubt it. That said, cats would have a far better chance of developing intelligence if they had fewer offspring as it would mean that the previous generation can't overwhelm the next one with numbers that make intelligence irrelevant as a survival trait.

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    $\begingroup$ Domestic cats can learn to open some kinds of door, maybe the humans left behind a vast planet-wide store of stasis pods containing meat (or catnip and ping-pong balls...) A cat with a big enough reach to open the older, simpler pods would be at a distinct advantage as long as the pods lasted, then its great^n grand-kittens might use their enlarged dewclaws to set the mouse-traps they found in the last pod... $\endgroup$ – Pastychomper thanks Monica Dec 17 '19 at 13:29
  • $\begingroup$ I don't think there is any way cats ideal conditions to evolve human-like traits, they are hunters, evolving to stand on two legs they would lose too much of their agility $\endgroup$ – BKlassen Dec 17 '19 at 16:42
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There are theories that human intelligence evolved at least in part due to the demands of caring for helpless offspring. Certainly in mammals and birds we tend to see that the brains of altricial species grow larger beyond infancy whereas those of precocial species do not develop hugely beyond infancy. Thus altricial species tend to end up more intelligent than precocial ones. The good news for you is that cats, like humans, are altricial (though not as strongly as humans).

What follows is speculation.

You need some kind of constraint to trigger evolution. Perhaps in your post-human world resources for cats become scarce, or they start to be out-competed. That's a plot detail. Those cats that are cleverer start to do better in terms of obtaining the resources. Suppose the mechanism by which a cat ends up cleverer is linked to its altriciality. Thus cats become more and more altricial, more and more clever, to deal with the resource constraint. At the same time, and maybe for related reasons, cats with more pronounced spur claws are favoured, and in time the dewclaw develops into a thumb-like digit allowing tool use. Some cats are already social animals living in prides or colonies, so again your evolutionary stimulus could encourage greater social reliance, ultimately resulting in more expressive / abstract language. All of the features above could mutually reinforce, providing a positive feedback favouring greater and greater intelligence. For added credibility though, don't expect that they would look highly similar to humanoid. Cats can already sit on their haunches to do things with their front legs (bat at Christmas tree baubles, for example) so perhaps they would just do this to use tools rather than fully standing upright, and maintain a four legged gait. Cat digestion is much more specialised to carnivorousness than human digestion is, so they are perhaps less likely to lose features related to carnivore specialisation (so they probably retain their clawed digits even if those digits become a bit more versatile, and they aren't likely to suddenly become arable farmers, though perhaps they might farm prey animals).

The timescale probably depends on how harsh the evolutionary incentive is: a mild incentive will result in a longer time to evolve or simply other factors driving evolution in a different direction. Too harsh an incentive and the species dies out without being able to evolve. Get it just right and you get your intelligent cats. To an order of magnitude 10 million years seems plausible, maybe longer, maybe a bit less.

Most likely it would never happen at all - human level intelligence has only evolved once so far out of millions and millions of species - but as author you do get to use the anthropic principle (felinthropic principle?) "I can justify that it could theoretically happen, therefore I choose to set my story in the universe where it did happen."

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They would probably never evolve into humanlikes, no matter how much time you give them.

Cats are predators, they don't need bigger brains to survive better. They are not even pack animals - yes, that is important.

For humans bigger brains were an immediate advantage, because it allowed better cooperation. It was not the skill to craft some spear that led to survival, it was the ability to hunt in packs, cooperating, that ensured a steady surplus of food. The ability to remember and identify a bigger variety of edible fruits to collect.

For cats that is no route to go. They hunt alone, they are not social and they only eat what they hunt.

You have way better chances with apes or even wolves than with cats.

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