Wouldn’t the simplest answer be, “Because the monkeys you see today aren’t the monkeys we evolved from?”
No, because it fails to challenge the unspoken premise in the original question–namely, that humans are better than monkeys, so much so that it’s impossible to imagine that humans and monkeys could co-exist.
Humans aren’t better. They may be bigger and smarter, but in a lot of environments, those attributes don’t count for anything.
I’d answer by asking the questioner how well he thinks he or she would do at living on grubs and berries (or whatever it is that the 100 surviving species of monkeys eat) in a tropical jungle. If he hesitates, maybe he’ll grasp the concept that, in many environments, monkeys are “better” than humans.
Kinda. Those are not the monkeys you are looking for. 
But people often think of evolution as being directed towards some goal, so why weren’t those other monkeys not directed along the same course towards the same goal. I think you need to explain more than just what you suggest to a lot of people, even if your proposal might work in some instances.
It would be simple, but it would also be incomplete. As I noted, if one’s perception of evolution is that populations are alleged to simply change over time, then we should have replaced any “monkeys” that we may have evolved from. Which, of course, we did.
The missing piece is that populations fracture as well as change, thus creating more and more populations of more and more divergent organisms over time. So not only are the monkeys and/or apes we see today not the ones we evolved from, they aren’t the ones they evolved from, either. We all share a common ancestor way back when which has gone extinct, as expected. And the subsequent species which that ancestor split into are also extinct, as expected. And so on and so on, until we get to the latest generations of each of those respective lineages – the apes we see today.
My interpretation of the question is that they think that either monkeys woke up one day as men, transforming, or that monkeys had human children. Remember how often creationists say things like evolution can’t be true since a cat never turns into a dog and other such nonsense. I think we’re overestimating their understanding of the process.
I don’t think we can presuppose what lack of knowledge the questioner possess, because you’ll hear this from a variety of people. Often, it’s just an attempt to set up a strawman but a Creationist, and the best thing you can do is simply correct the mistake before he throws up another strawman. If someone is accepting of the idea of evolution, but is just not well educated on the subject, it would behoove the person answering the question to probe deeper to find out what particular assumptions the person has that are incorect. In the US, at least, we do a terrible job of teaching evolution in public school. I don’t think that has much to with anti-evolution, but just the poor overal quality of US public education. I am often surprised how many misconceptions my otherwise well-educated friends have about teh subject of evolution. What we typically get-- maybe 2 weeks of coverage in a HS biology class?
I don’t think it’s a stupid question. What it is is a classic example of begging the question: it assumes we did “descend from monkeys,” whatever that means to the questioner, and poses the query based on that assumption. It’s the kind of logical trap that is easy to fall into, whether one is smart or stupid.
Actually there is not (if you consider fossils to be “cryogenically-frozen”). Its a pretty common in problem Paleontology to decide if two fossils from difference period are part of the same species.
Fossils have this distressing tendancy to not mate with anything, though, which makes it a bit hard to apply the Biological Species Concept. You can still make guesses about whether they’re the same species, of course, but you can’t be sure.
If people and monkeys evolved from single-cell organisms, how come there are still single-cell organisms?
And how could all this happen in just 6000 years? 
Same thing everyone has been saying-- not all the single-celled organisms evloved the same way.
This is GQ, not witnessing. Try 3.5 billion years.
Well, I’m a little intimidated questioning someone with your user name about evolution, but is it really true that the common ancestor (let’s say for example between chimps and humans) went extinct? To me, that implies that the population of that critter reached a dead end, no longer had offspring, and died out.
The way I thought it happened is that a population of apes split, some maybe ended up in geographic areas where there were more trees, the other part of the population ended up where there were fewer trees. The population in trees continued evolving to get to modern chimps, the population on the plains continued evolving into modern humans. And in this scenario, the most recent common ancestor population never went extinct, it just split and changed in two different ways.
I think you missed glee’s humor. I think he’s British, so maybe that explains it. His post was poking fun of the young-Earth creationists.
Yes indeed.
I apologise to anyone misled. :o
I was trying to rephrase the original question to promote understanding by including single-cell organisms, which I understand still co-exist with their various descendants.
For the record I am a male Brit atheist who believes in evolution.
It’s pretty easy to understand if you ask yourself where they are today. Can you point to the population that didn’t go extinct? If you can’t, then they are extinct.
We do expect that common ancestor of humans and chimps looked more chimp-like than human-like, that doesn’t make it a chimp, and doesn’t mean that it wasn’t substantially different from a chimp, both morphologically and genetically.
Think of it like language. Latin is extinct, but it left (at least) 5 descendants: Portuguese, Spanish, French, Italian and Romanian. We don’t even call Italian “Latin” although those speakers reside in the same general geographic area as the native Latin speakers.
If you’ve ever been in an evolution debate in GD, there are several posters who would have posted something just like you did, and they’d be serious about. I didn’t recognize you from any of those debates, so it wasn’ clear. So, as you Brits like to say-- Carry on!
But I can point to the population (or their descendants) who didn’t go extinct - I would point to both chimps and humans. Nothing here went extinct (in the big-picture, simple sense - you can always have small offshoots that died out such as the Neanderthals).
Let’s take the simpler case of evolution of a population without a branching (speciation) event. For example, suppose that humans never branched off that line four million years ago. That creature was as it was, and supposedly chimps would now be identical to what they are. The population evolved, but you wouldn’t say that the four-million-years-ago pre-chimp creature went extinct, would you? You could also make the exact same argument by supposing that the chimp line never branched off, and that creature evolved into only modern humans. In either case, it didn’t go extinct, it just evolved.
Why would it be otherwise if the only change to that scenario is a speciation event? The pre-human-chimp creature never went extinct, it evolved. Extinction means that the population produced no more offspring. It’s an evolutionary dead-end, at least the way I understand the term is used.
Until we get a sample of a 50,000 year-old proto-human, prancing around in a bikini trying to seduce us, we won’t know if we’re the same species — therefore I believe “extinct” is a dicey sort of word to use. It’s safe to say that it doesn’t exist now in the same form as it had 50,000 years ago, because it’s safe to say that very few large animals exist in exactly the same form now as from that time period.
And it could’ve split three ways, or five: different kinds of trees, same trees in different climates, varying degrees of forest density. We don’t need to suppose a mass migration to a vastly different environment, because evolution takes place constantly. All we need to suppose is time over which it can occur.
Not so much reached a dead end, but was gradually replaced. Think of one large, parent population. This is the ancestral population. Part of it fractures off, and becomes separated, by whatever means, from the main body. The two now-separate populations evolve independently. Over time, the main population continues to change and adapt. Subsequent generations are, per the theory of natural selection, generally more adapted than prior ones, so will tend to outcompete their older conspecifics. The gene pool comprised of the genes of the ancestral stock will tend to decline, and the newer genes will tend to be favored. This is what I was referring to above by “anagenesis” - the population gradually transforms over time, with occasional splits occurring and creating new branches. The old, original stock is eventually replaced by a newer, better adapted population.
Now, whether or not you wish to claim the new population is a new species or not is a matter of debate. Per the phylogenetic species concept, it would not be. Per the morphological or biological species concepts, they probably would be. In the latter cases, then, it could be argued that the ancestral stock is therefore extinct, even though the transition to the current state was one of gradual change, rather than the population meeting an abrupt end (as “extinction” is commonly interpreted).
It is this latter view that I was using as I’m not of the opinion that the phylogenetic species concept is suitable for application over large stretches of geologic time. Otherwise, as all current species are of lineages continuous with the original life form, all must therefore be of the same species as that original form, and that way madness lies. The PSC seems better suited for shorter time ranges and a clear, unbroken succesion being available to examine. Since we are essentially operating from the fossil record, the populations we do see are typically determined to be distinct species (based on various other species concepts), and we can thus say that the earlier forms are thereby extinct.