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I barely know anything about biology and realize that this might be a stupid question, but I'll ask anyway! I know that species "transform" into other species through the process of evolution. Many species around today still co-exist with the species in which they evolved from, right? Actually, is it correct to say that all species coexist with some common ancestor?

Anyway, my question is; if the monkeys that we evolved from are still around today, then where are all the in-between species. Are there still early humans, like Neanderthal's or Hominids or what have you still roaming around some where?

If all early forms of humans are gone, is it because the more modern humans had a greater evolutionary advantage? But wouldn't these less modernized humans have those same advantages over the less evolved monkeys?

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    $\begingroup$ This 'missing link' question has been posed many times here. I think a reading list is the best response and should be posted in context of closure process. $\endgroup$
    – daniel
    Aug 3, 2014 at 11:55
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    $\begingroup$ I disagree about this question being off topic. The help center specifically states that "general questions about biological concepts" are suitable. This question addresses common misconceptions about the evolutionary process. Of course, I'm new here but I wanted to share my opinion. $\endgroup$
    – Michael S Taylor
    Aug 4, 2014 at 3:09
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    $\begingroup$ I too do not see how this question is off topic. If it is a duplicate, then you could perhaps link it, or perhaps suggest a source in which I could find it? I have found some of the answers here helpful $\endgroup$
    – JonHerman
    Aug 4, 2014 at 4:32

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This is a common misconception about evolution, many skeptics ask something along the lines of "If humans evolved from monkeys, why are there still monkeys?" The answer is that evolution is not a linear process of one species becoming the next species becoming the next. Species branch off much more like a tree. At some point in the past the last common ancestor of humans and monkeys split into two directions, one that became the apes including humans, and one that became modern monkeys. Evolution did not stop for either branch, but only our branch became humans, after several more branchings. Sometimes species adapt and evolve without major changes in morphology, for example modern turtles look a lot like turtles from 100 million years ago, but this doesn't mean they haven't evolved.

The intermediate species are often lost with time as environmental conditions and competition changes. For example, if one early human group found itself competing with a slightly more advanced human group with better tools, the more primitive group would have trouble getting enough food and eventually die off, leaving the more advanced group to pass its genes on.

Now, if those more primitive humans were more suited to a particular niche, they could survive there. Lets say they could climb trees better ( assume REALLY primitive ancestors, barely out of the forest ), they might survive in the forested areas while the more advanced groups become dominant in the grasslands. Something like this is why our ancestors didn't totally displace monkeys, the monkeys were better suited for their forested ecosystem. If those same monkeys had to live on dry savannas we would have eaten them all long ago.

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  • $\begingroup$ Cool, thank you for your answer. I agree completely that it makes perfect sense why there are still monkey's around today. So I think what you're saying is that I can (vaguely!) think of it like this: $\endgroup$
    – JonHerman
    Aug 3, 2014 at 3:12
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    $\begingroup$ At the branching point between the common ancestor of modern monkeys and modern humans, there were sort of two scenarios which evolution acted on, one in which the "to be monkeys" were better suited and the other "to be humans." In the former, the monkeys won and still strive in those areas today. In the later, the "to be humans" won. But in this setting, the modern humans were just evolutionary superior, and so the in between species of human eventually died out? $\endgroup$
    – JonHerman
    Aug 3, 2014 at 3:12
  • $\begingroup$ Worth noting that they took a fairly long time to die out everywhere. The Denisovans(Siberia), the Neanderthals(Europe), and probably some others all stuck around for thousands of years after modern humans evolved and spread out of Africa. As these 'more human' hominids shared ecological niches(bipedal, relatively smart, thumbs) with early humans, we outcompeted them for resources(small game, territory) while we don't compete as much with say, orangutans. They live in trees and eat leaves and fruit, but we need protein and fat for brain-making. $\endgroup$
    – Resonating
    Aug 5, 2014 at 16:44
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I think other answers have explained natural selection, but I think it is also important to note that species boundaries are applied in retrospect. This sounds blindingly obvious, but when presented by skulls from two species, such as Homo erectus and Homo sapiens, many will then ask where the evidence is for the species that came between those two.

There are several reasons why you can't see all of these in-between forms:

  1. The fossil record is imperfect. Although there are no longer any "missing links" in the fossil record for the evolution of humans from our most recent common ancestor with chimpanzees, not every change in skeleton shape has been preserved for us to look at.
  2. Species boundaries are applied retrospectively. This means that when we find a new set of bones that seem to be in-between two species, we give these bones a new species name, because they clearly don't belong to the other species we've already identified. The bones actually represent one of the "in-between" forms that people are asking about, but we can't just label it "intermediate" or "missing link". It has to be categorised as a new species or sub-species.
  3. You're not technically looking for an "intermediate". It's not that chimpanzees are an "intermediate" between humans and some ancestral species. It's that humans and chimpanzees share a common ancestor. When you see a pictures of a neanderthal, they might superficially look like an intermediate between humans and chimpanzees, a sort of hybrid between the two, but that's not quite right. It's not that chimpanzees eventually became neanderthals, which eventually became modern humans. It's actually that humans and neanderthals share a common ancestor and that ancestor is no longer around for reasons given in other answers. Similarly, neanderthals and chimpanzees share a common ancestor that is now extinct. My point is that if you're looking for something like a "crocatoo" that's a hybrid between a crocodile and cockatoo, you won't find it. Yes, crocodiles and cockatoos share a common ancestor somewhere in their family trees, but there's no reason that it will look half like one species and half like the other! It might look nothing like either of them!

If you're looking for more information on evolution, I'd highly recommend "The Greatest Show on Earth" by Richard Dawkins. If you want citations for the points I make, you'll find all of it in there. It explains this stuff quite clearly, with ample evidence to back it up (assuming you can put up with his occasional rants about young earth creationists...)

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If all early forms of humans are gone, is it because the more modern humans had a greater evolutionary advantage?

If you take an environment where species dwell, three things could have happened:

  • The population got smaller and smaller, in a given environment, and then bam the last ones disappeared without producing any offspring. This is because population as a whole wasn't reproducing as fast as they disappeared, for a variety of reasons. By disappeared I mean: went away to other environment or died out.
  • In another environment, so much changes had spread through the population that at one time the new offspring was born with their genotype now "too much" different and thus incompatible. By "too much" I mean this: they could still mate with both partners from their population and with "less changed" neighboring populations, but they could only produce a fertile offspring with former but not with the latter. We nowadays refer to such situation as "they became new species". From this point they obviously couldn't spread "their" genetic changes anymore to other environments via reproduction (spreading parts of genotypes). Their offspring would be infertile. They only could spread "their" genetic changes by sending whole groups of folks (complete genotypes) to other environment to try and cope there. And sometimes to kill others interfering, because, hey, that's what living creatures sometimes just do.
  • The population lived without "too much" change in the genotype and still exists today in the given environment. Without "too much" change means they were unchanged or rather changed slow enough that at any given time they could leak their changes to other populated environments via reproduction (they kept being the same species as their neighbors).
    • I have written about genetic "changes". You call these "advantages" and even "modernizations", but for the sake of argument it just doesn't matter (and only blurs the picture with the unnecessary concept of "superiority"). Advantages in one environment are disadvantages in another.
    • I use "environment" here for simplicity, but a more proper term would be a "habitat".

We don't observe any early humans today. It seems that all their populations have met one of these two former fates.

Also, you tend to overuse high-level abstract terms that distract you from thinking what have actually happened at low level. "Evolution" does not "act" on any "scenario". This is just a bit too much of anthropomorphism.

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  • $\begingroup$ It would be fantastic if you included some references in your response! $\endgroup$
    – Behzad Rowshanravan
    Aug 3, 2014 at 12:28
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I know that species "transform" into other species through the process of evolution.

I don't think you are thinking about that right.

We have a population of organisms that are breeding together. We humans label that a 'species'. That population has descendants, and over time, the population changes, and when we humans think that the new population look sufficiently different from the old, we label them a new species.

Many species around today still co-exist with the species in which they evolved from, right?

You might have founder situations, where a small sub population breaks off and inhabits a new environment, and changes a great deal more over time than the original population does, such that we continue to label the original population the same species, while we label the offshoot a different species. But I think what happens more often is that the alleles that cause humans to label a population a distinct 'species' dwindle to nothing in the descendants, and then we say that the original species is extinct, replaced by the new one. but that's a matter of labels: there is continuity in that the new 'species' is just the descendants of the older one.

Actually, is it correct to say that all species coexist with some common ancestor?

No. Can you even name any examples where you think this is true?

if the monkeys that we evolved from are still around today,

What on earth makes you think that's remotely true? For one thing we aren't descended from monkeys. We are descended from primates that were more like apes, not monkeys. There is no living population of primates that we would categorize as being the same species as that non-homo sapiens ancestor population.

Are there still early humans, like Neanderthal's or Hominids or what have you still roaming around some where?

I'm confused how you think an organism or a population existing in the 21st century could be "early". All the hominids walking around today are members of homo sapiens sapiens.

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