If all humans (but no other species) just suddenly disappeared, leaving all of their structures standing, how long would it take for an intelligent species as dominant as the humans to evolve? Would the disappearance of humans change anything?
As sad as it sounds, the safest assumption is never (or forever).
It has been stated in the comments by @ratchetfreak: The dinosaurs roamed world for million years without developing intelligent society. Or they have been so clever to take all technology with them when leaving Earth, or so unlucky, that the Yucatan asteroid wiped out all technology when it fell down to Earth.
But back to reality.
If you need to develop intelligent life again, amongst the best candidates are chimpanzees. So you could plausible repeat human evolution again and let chimps evolve to something close to Homo Sapiens. That according to Wikipedia should take 2.3 million years
You have to ask yourself the most important question:
What defines "intelligent life"?
Is it buildings? You have termites
Is it society? Bees, ants, termites.
Ask yourself what you want to achieve in your world. Then, being you, I would work backwards from that point: What do I need for intelligent rats having society like ours? Is it plausible? If its not, how do I make it sound plausible? (Come on, radioactivity mutation was used so many times that no one is even surprised.)
There is no way of giving a sensibly supported answer. We have a sample size of one, and we don't know what the requisite steps along the way were.
It is quite plausible that many of the steps have already been achieved in species such as chimps which share considerable evolutionary history with humans and thus these species would evolve new forms of intelligent life pretty quickly. Alternatively it may be that the conditions that led to humans are so incredibly unique it will never happen again. We really don't know.
On the subject of dinosaurs; this is rather misleading because the ground conditions for humans carried on evolving over much longer periods. Based on crude measures of brain size there is good reason to believe that the "typical" mammal is a lot more intelligent that the "typical" dinosaur so it may be that dinosaurs simply didn't have the ground conditions for intelligence to take off. Also, remember that while dinosaurs were - at least - 65 million years less evolved than humans this isn't true of today's life.
If I was take a personal guess, I would think that another primate would evolve intelligence within a few tens of million years but there that's little more than a guess.
Evolution happens on time-scales that are of far greater magnitude than the length of time our current mediums can hold information or any other evidence like buildings. Buildings and landfills break down before intelligence really shows up. CDs are an exemplary back-up medium, yet they only last 20 yrs without degradation. Which means you gain no benefit from an intelligent precursor species over an unintelligent one.
Time taken to evolve intelligence is highly variable. Intelligence is not a foregone conclusion. For example, if any of our germ aliens ever end up existing I doubt we would place their evolution to intelligence as anything other than improbable. Humans being gone would only change how the variables in the ecosystem are set. Extinctions from transplanted species probably drops, stable ecosystems have a better shot at staying stable longer, etc.
Given that Humans are exhausting planetwide limited resources, and otherwise fouling their living space, who says intelligence has yet evolved, whether Humans are present or not. If intelligence equates to avoidance of species extinction perhaps sharks have it, as long as they stay away from Humans.
It's impossible to answer this question, as others have suggested the process may take millions of years or may not occur at all!
Having said that I'll have a go! I'm going to assume for the sake of argument that "intelligence" is about a species using teamwork, plans and tools to work together to succeed rather than simply learned behaviour (which all species display when their parents teach them how to hunt/find food).
Evolution does not guarantee intelligence, evolution suggests that the best survivors will flourish but the weaker evolutionary options will be out competed. The only way a species evolves intelligence is if the intelligence gives it an advantage when it comes to survival or reproduction.
At some point in our pre-history our ancestors began to outperform other more powerful species because of their intelligence, this gave them an evolutionary edge and allowed our species to flourish. The ancestor to the crocodile gained that edge by growing a ridiculously strong bite, the shark... well (I'll come back to them later).
We're actually talking about two sorts of evolution here, genetic evolution (the process of the brain growing bigger and mutations working there way into the population), this take millions of years and cultural evolution (learned behaviour, skills, language, behaviour). This cultural evolution is much faster... from a biological perspective we're not that different from Neanderthals, what has changed is our culture and our education. If you draw similarities between apes and our ancestors the process could be significantly quicker. Neanderthals began agriculture about 8000 years ago, it's possible that you could see a rise of another species (most likely some form of ape) in a similar sort of timescale.
However if we're waiting for other species to "catch up" genetically, for example for dogs to evolve to have the mental capacity of some other animal species this process could take millions of years - assuming it happens at all!
Which brings us back to the shark, it's commonly believed that the ancestors of the sharks which were around 450 million years ago were very similar to the species of shark we see today. They've had 450 million years where they've never been out evolved and they've never needed to develop intelligence*!
*I like sharks... from a distance!
When I think of this topic, the concept of the Singularity comes to mind, of which we are "on the cusp" so to speak.
Human beings evolved from lesser species, which evolved from single-celled organisms, which evolved, literally, from molecules, energy, and luck. Looking forward, human beings developed technology, which can be thought of as the next epoch in universal evolution. A whole ton of evolution happened in the first few seconds of the universe, and since then things have slowed down a bit and we've settled on matter and energy as we know it. Then life began to evolve (on our planet, and likely many many many others).
Once technology becomes "self sufficient", it really won't matter what happens to human beings. The technology will represent the "level of evolutionary intelligence" that we've achieved. Even today, if human beings became non-existent, some of our technology would continue to operate, and even "advance" to a degree. This will apply even more so as we advance our technology. Similarly to how human beings will continue to "evolve" even if all of the monkeys were to become extinct today (or how we've evolved in the absence of the Dinosaurs). Similarly to how stars and solar systems will still "evolve" if our solar system were to become non-existent today. Similarly to how gravity will still exist regardless of what types of matter our universe consists of...
That all being said, the probability of human beings becoming extinct, and "another" species achieving our level of "intelligence" on this planet are astronomical. Our planet is lucky enough to have evolved our species; it's a lot to ask that our planet be the one to evolve a species like ours again. Although, our planet has an edge, in that it has evolved intelligent life before...
Really it's a philosophical issue: do you believe we are alone in the universe, or not? If you think human beings are the "most intelligent" creation of the universe, then our extinction doesn't bode well for the future of intelligent life. If you think the opposite, then it's almost a given that somewhere else, there is a level of intelligence that rivals our own...even today (although "today" is a relative concept in the scale of the universe).
Actually, the best bet right now to take our place if (or, God forbid--when?) we go extinct would be bonobos, not chimps--they're even more intelligent, more sociable, less aggressive/violent, and yes, a separate species.
It has been posited that, eons ago, a troodon--a (theoretically) highly intelligent therapod dinosaur--might have evolved into an intelligent, humanoid creature, if that big rock hadn't dropped out of the sky and wiped them all out.
No way to know, of course. Earth has a leg up, in that it's already shown capable of sustaining an astounding diversity of creatures, as well as intelligent life. Still, there's no guarantee that anything would happen: it would require a relatively small population of animals with the right genetic potential to become isolated for even the chance that evolution would occur. But if humans disappeared, and an isolated population of bonobos, say, began to evolve into something else, something more--then my best guess is that the process would take about seven million years (about the time it took for the common ancestor of humans and chimps to evolve into us; we're really the only example we have to work with so far).
Around 4300 years ago
From this article on the BBC:
In the rainforests of west Africa, the woodlands of Brazil and the beaches of Thailand, archaeologists have unearthed some truly remarkable stone tools.
It's not the workmanship that makes them special. If anything, a casual observer might struggle to even identify them as ancient tools. It's not their antiquity that's exceptional either: they're only about the same age as the Egyptian pyramids.
What makes these tools noteworthy is that the hands that held them weren't human.
These stone tools were wielded by chimpanzees, capuchins and macaques. The sites where they have been unearthed are the basis of a brand new field of science: primate archaeology.
The tools are crude. A chimpanzee or monkey stone hammer is hardly a work of art to rival the beauty of an ancient human hand axe. But that's not the point. These primates have developed a culture that makes routine use of a stone-based technology. That means they have entered the Stone Age.
More on the article itself.
Maybe if we vanished, apes and monkeys would expand into our territories, gaining enough resources to properly develop tool-using traditions without interference from their long-gone hairless cousins.
Quite a bit of intelligence may develop within a few million years. However, an industrial culture like today may return much slower or not at all, since all easily available resources like copper deposits for early metallurgical experience have been used already. Easily available energy sources are used up as well, and no culture will go from Stone Age to photovoltaics directly. A neo-human population with stone-age culture will not be able to exploit resources that require deep mining the way we do. Domestic animals are another Topic. Some animals like cows have evolved in a way that they may become extinct when mankind would disappear. So the next culture would have no cows to start milk production with. However, other domestic breeds like sheep should most probably remain.
One factor to consider is how many "puzzles" humans have left around. A lot of animals have been co-evolving with us for millenia, and adapting to the challenges we create for them. For example, we hoard food, but we don't just keep it in open piles, we keep it in pots and packets, and animals that live around us have an incentive to solve these "puzzles" to get to this food. So, arguably, a lot of animals are currently on an evolutionary path that rewards intelligence just by virtue of having us around, in a way that wasn't the case when we were coming up. Obviously if we disappear the supply of new puzzles will stop, but there'll still be an advantage for the animals that can figure out how to use some of the simple mechanisms we leave around. For instance, an animal that can work out how to open a door, has the advantage of having a contained or semi-contained habitat to live in; an animal that can work out how to use a water pump can keep themselves watered while their competitors die of thirst, etc. etc.
So, in answer to your question, "how long will it take for a second intelligent species to evolve", my answer would be, probably* not as long as it took for the first.
*Obvious disclaimer being that it is impossible to talk about any sort of concept of probability for a factor that we only have one point of data for...
One of the carnivore / omnivore social predators (apes, bears, wolves, etc.) with pack hunting skills and a substitute organ for the "human hand" (like an elephant with trunk) able to manipulate things and tools and enough evolutionary / environmental pressure to adopt or steady change.
Considering our rise as a great ape, a million year is my earliest guess.
If humans would disapear and other land mamals with large brains will remain. You would need the development of another branch like the one it happen 6 million years ago when genus Apes and genus Homo was diferenciated. The question is that you dont know what trigger this development (tool shaping, social structure, communications). What seems to be a fact is that the different species of genus homo achieved a different level of sofictication in tool development control of fire, hunting strategies which were passed to the next). As each new species of homo developed different sizes of brains (even within the same species across hundreds of thousands of years you can see this development) so arround 3 million years ago you can start to talk about stone age technologies or as they are called industries). We find for the case of our closests relative the neantherthal, even having similar brains to us and similar time spands complex societies were not developed (maybe because the gropus were small in size - it is estimated that no more than 100,000 existed at once) for example that when an interglacial period occurred within their existence (125,000 to 115,000 year) ago), they were not able to create agriculture possibly because for most of their existence earth was within a glacia period (adaptation) and due to their small population. While for example at the time of the invention of agriculture the population of homo sapiens was 4 o 6 million individuals so social complexity also seems to play a role.
So my guess is between 5 and 15 million years from hominids and possibly hundreds of millions if from other mamals.
I highly doubt it, and it's all because of the timing. Some other animals have been considered highly intelligent--elephants, dolphins, corvids and New World monkeys. They've all been around for many millions of years longer than humans, so why that shouldn't make them smarter than we is a legitimate question.
You’ll have to consider the environmental effects that humans vanishing would have as well. No more farming and burning fossil fuels suddenly would end the Anthropocene, but not instantly revert climate change and terraforming. It would take a slightly different path than with us and yes, this may have an effect even on the million-year scale. There would be noone to counter neither erosion nor forestation. Many highways and canals would fade away but some would form the basis for seemingly natural barriers. This, together with preexisting and interdependent geologic and climatic forces (of a much larger scale) would shape the environmental pressures that drive evolution.
We don’t know for sure which conditions were mandatory for the genesis of homo and later homo sapiens, but they happened once (at least) and that means they could happen again, albeit probably in slightly different form, to boost the physical and later psychical limits of another animal within a lot of generations. After the body had evolved and our mind became conscious it didn’t really take us that long to develop society and science.
There are certain properties of human body and society that made us so successful. They need not repeat in the same way, but for some species, especially apes or monkey and other mammals, it’s likely that they are beneficial as well and some of them have a head-start. This includes free hands to make and wield tools (incl. clothes to counter otherwise unsustainable climates later on) which requires upright gait if no other flexible, sensible, strong limb was available (like trunk, tail or tongue, but preferably two or more), which like increasing brain/head size makes birth more complicated, dangerous and painful and hence requires strong social groups wherein language can develop (maybe again first gestured/signed, then voiced) to coordinate actions and easily pass on knowledge; also a flexible digestive system allowing for a variety of diets and thus adapt to many different or changing environments.
I don’t think carnivores, e.g. cats and dogs, will ever be pressured enough to evolve that much. It’s more likely omnivores or perhaps herbivores, who can eat fruit not just grass or leaves, will succeed after several hundred-thousand to few million years. Unless the climate changes dramatically, mammals are probably a safer bet than e.g. reptiles, birds or even fish (incl. whales and dolphins), but I wouldn’t rule them out either. Hatching eggs, for instance, could be an advantage – the ability to fly or swim less so.
Keep in mind that during recorded history which slowly approaches ten thousand years there have not been observed any significant lapses in freely evolving animals or plants, but those bred and curated by humans have changed a lot. The quickest path to conscious, sentient beings besides us is one paved by us, be it by genetic modification or through advanced technology. That could happen in just hundreds to thousands of years, maybe even in tens, which is several magnitudes less than with undirected evolution.
And then there is also the hive mind that maybe also could develop sufficient intelligence to become self-aware. That would take much longer to happen than a second coming of the mammal.
By the way, as cities crumbled they slowly became the possible sites of future mines since we already moved and concentrated lots of natural resources there. Some other remnants could also last long enough to be beneficial for a future civilization, even cultural ones.
To expect just like another humanoid being it may be won't occur at all.
But if dominant is the keyword here, maybe in just few years a population of rats would be exploded. While there will be small to none chance of them evolve to be just like us, they would likely will advance and dominate. Right now they are already everywhere, lurking in the dark side of man made structures globally. When there wasn't any human, leaving our live stock and food unguarded, they would stepped out and claimed it for themselves. When there wasn't any of our processed food left, their rapid breeding would sustain themselves a bit longer, made them cannibalistic before they expanded to rural areas and eat anything they could. Imagine a cannibalistic enormous half bald sewer rats that roam on post apocalyptic cities, it would cause a mess more than zombies can ever did.
As others have pointed out, it might take a long time -- or never happen at all. We don't have good data.
If humans suddenly and silently vanished, leaving everything else as is, then we'd have a situation markedly different than evolution to date.
Short term, there'd be buildings, relatively non-perishable food, water -- and all sorts of human artifacts, just waiting for a similar species to make use of them. What species are likely to do so?
- Somewhat intelligent species (primates, some cetaceans)
- Animals that can manipulate human artifacts and especially tools (primates, elephants)
- Animals that have seen humans and their artifacts in use -- especially tools and simple weapons -- so any pet species or lab animal, but especially monkeys and chimps.
With the humans out of the way, I suspect that a few lucky monkeys and chimps in urban areas would soon be living large on what we'd left for them. Those animal's offspring would have a distinct survival advantage.... Personally, I think that there'd be visible evolution toward man-like intelligence in a hundred generations, so ballpark a thousand years.
Like the comments have stated, What kind of intelligence are you looking for?
But, From my knowledge (as no expert in anything whatsoever), Humans have extremly good cumulative intelligence: as in what is learnt in one generation is passed down onto the next allowing for innovation and improvement over relatively few generations. This is due to the fact that humans only need to see something happen once or twice before they learn how to do it themselves (unlike chimps whom every generation have to learn an ability from scratch all over again).
Another factor to consider is what animal they are evolving from. For example, Humans could create and use the tools they did because their evolutionary ancestors had paws (hands) made for gripping. Dolphins on the other hand, whilst they are intelligent and do use tools, have only their mouth to grip onto objects. Therefore if you wish to create a species similar to humans they must not only have the right type of intelligence, but also the means of which to use that intelligence in a manner similar to a human.
So to conclude, There are plenty of animals with intelligence near or on par with humanity but overall to create what i think you're looking for you need: A social species (in which social intelligence can grow), cumulative intelligence (where ideas can be spread and improved upon quickly), an environmental pressure which encourages forethought and creativity (such as rapid climate change), and a species with the physical abilities necessary to use, interact and create in a manner similar to humanity.
Society is more important than intelligence in the evolution of technological adept beings.
Everything you know about how the world works is learnt. You might think yourself incredibly clever, but the fact is that what you're thinking at any point is built upon thousands of generations of learning and lost learning.
Without an appropriate societal backdrop, learning is lost. If a solitary creature learns something, of what use is that to it's species? None. If it passes it on to it's children and they die [or otherwise fail to engender use] before passing it on in turn, what use is that to the species? None.
Learning requires more than just invention.
Intelligence is not linear. A human brain is not evolved to nor used to simply think from A to B, a human brain performs multiple simultaneous tasks some of which interfere with or aid the 'A to B' thinking process.
We can assume that non-human intelligence will have to operate in a similar fashion, given our experience of various types of system architecture, superior hardware is not the only requirement for a superior system.
I bring this up because it's entirely plausible to have a brain with inferior (apparent) hardware to a human that actually can think logically, that could streamline it's own cogitative proces, that cerebral functions were separated more clearly from emotional responses or bodily demands etc etc and thus offer superior results (in at least one sense.)
We can hardly say any aspect of our behavior is 'bad' when we are capable of doing anything any animal can do..and better..and what we can do would not have reached this point were it not for some character traits that might seem suboptimal in retrospect.. but..
Imagine an organism that through some quirk of evolution never lied or bore false witness? The time saving! I wouldn't need to check fifteen different scientific papers and still wonder "yeah, but their dept is mostly funded by x or y"
Granted it's true that humans to the best of our knowledge are unique in the universe, but it's possible intelligent societies could evolve within just a few thousand years, because as I say it's not about pure native intelligence, but the ability of a species as a whole[or at least in significant groups] to benefit from technology, which in turn then allows the selection process to favor intelligence and better ability to manipulate tools over sheer native survivability.
It's a mistake to think one thing happens then another with any kind of finality, evolution is concurrent with life, society evolves with technology, one generation might actually not be as capable as the last, despite the most intelligent reproducing more...etc
Look at societies today, there's nothing about flooding, rising sea levels, etc that humanity can't cope with as a species, but local interests and local resources and local planning often simply aren't up to the task, one group ignoring warnings from other localities that they need to work on their irrigation and drainage systems is not a sign that the whole species is flawed..just as if one bee attacks a camper isn't a sign that all bees ought be poisoned.
For remnants of human civilization: a dog with a little experience knows the difference between a bush and a fence even if it doesn't watch it being built/growing. People tend to make gates, let's look for a gate. In a society capable of basic tool making this would [clearly] be a massive influence, the differentiation between synthetic & natural allows us to infer purpose, that inference allows us to imagine of what use that construct and it's purpose might be to us. No different to seeing another human using a tool we've never seen before. Granted ofc the purpose might be beyond divination, or billions of man hours might be sunk into talking about how "we do/n't know why the gods built this" but people have shown the ability to do this about storms, particularly big trees, cherry blossoms, etc etc, so it can hardly be called a handicap..
Speaking of dogs..if mankind (and mankind alone) vanished, dogs would obviously spread like wildfire. I'd give them the best chance of dominating every landmass..and given hundreds of millions of them each having their own go at 'society' you might get an intelligent society out of them sometime within say..50k yrs. Ofc I say that coz more bipeds would be boring.
Case in point, the intelligence of turtles has been steadily increasing for about 210MY, despite setbacks like the K-T event. Its possible that in the absence of humans or a postulated parallel Universe where for whatever reason the Neanderthal/AM human crossbreeding introduced a fatal genetic defect, parasite or virus resulting in extinction in about 61.3MY turtles would have reached the intelligence of dogs.
Of course, corvids and small mammals would have reached their zenith long before but its entirely possible that progress could stagnate due to brain size limitations. The brain is more complex than mere size and African Grey parrots seem to be the upper limit (2.3yr old child)