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Layman here. So I have never really quite understood this facet of human evolution, (or any other for that matter), in that, I understand the evolutionary process, but I get lost on the 'border' cases.

For example, we, as humans, evolved from monkeys, (to use the colloquial term, I am not a biologist by any measure).

My question is, doesn't this mean that at some, discrete point, there had to have been a human, whose parents were not? If that is true, how does that work, in the sense that we now have species1 giving birth to species2.

If not, then how exactly does this border case work? The only other alternative I see, is that the borders are 'fuzzy', but then that necessarily means that the definition of a species is itself fuzzy, which I understand is not the case.

Thanks!

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Take a bucket of blue-dyed water and start slowly pouring yellow-dyed water into it. Is there a discrete point at which it becomes green? –  Russell Borogove Aug 24 '12 at 18:23
    
@RussellBorogove Interesting - please see my comment/question to Konrad on this matter though. –  Mohammad Aug 24 '12 at 19:10
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6 Answers

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Actually, your last paragraph is more the case than not.

There are currently three common definitions for delineating discrete species:

1) Phenotypically different from related species (looks or acts differently).

2) Produces viable offspring in the wild.

3) Some % of genetic difference.

There are strengths to all three:

1) Very easy to ascertain and measure.

2) Most common conception of a species.

3) Genes control the first two, so genetic divergence gets to the heart of the matter.

There are also weaknesses to all three:

1) Is notorious for mis-labeling and missing species.

2) Some species which can mate and produce fertile offspring under enclosed conditions do not do so in the wild (Tigers and Lions, for instance).

3) The amount of divergence has, thus far, been completely arbitrary. If there is a certain % or patterns of mutation required in the genome, science hasn't yet discovered it.

The fuzzy definition of species, combined in the not-exactly-intuitive generational-type thinking required for understanding evolution, and the answer to your question is (at least to the best of my understanding) the following:

Yes, at some point one of our ancestors gave birth to the first Homo sapien that was somehow genetically different from its parents. However, the magnitude of the difference is probably not as great as you might think.

We've already observed our closest evolutionary cousins, the Bonobos, making basic tools through flint napping: http://www.newscientist.com/article/dn22197-bonobo-genius-makes-stone-tools-like-early-humans-did.html

It's also possible that disputes between male chimpanzees are mediated by an older female: http://www.cpradr.org/Resources/ALLCPRArticles/tabid/265/ID/121/Primates-and-Me-Web.aspx

And that both Chimpanzees and Capuchin monkeys can be taught the concept of currency (which, somewhat comedically, they then used for prostitution): http://www.nytimes.com/2005/06/05/magazine/05FREAK.html?ei=5090&en=af2d9755a2c32ba8&ex=1275624000&partner=rssuserland&emc=rss&adxnnlx=1118160068-1EGJuan4FJH1LooxHYd5/g&pagewanted=all

Then there's the everlasting impact of Koko, the Silverback Gorilla who was taught - and perfectly capable of replying in - sign language: http://en.wikipedia.org/wiki/Koko_%28gorilla%29

The idea that humans jumped onto the scene with unforeseen amounts of intelligence and capability probably isn't what happened. Obviously we are capable of constructing and using the most advanced tools on the planet, but this is after several thousand generations of innovation. The very first human might have been more intelligent (or at least had the capacity to be), but otherwise probably fit in pretty well with its parents and other relatives since the vast majority of what we learn comes from our parents and personal experience.

Then over time the number of individuals with the capacity for higher modes of thinking increased as a result of the genetic inheritance of whatever mutation created the first human. The first human, to put it simply, was successfully able to pass on their mutation which gave them our unique traits, and their offspring were also successful - until you have an entire population of humans living amongst each other. Eventually our innovative capacity lead, step by step, to our dominant position on the planet.

Even now humans are yet evolving. Lactose tolerance (the ability to consume dairy products after childhood) is a very new trait among humans (and unprecedented among all mammals) only a few hundred generations old (roughly 10,000 years) that evolved twice in separate populations of humans (North Africa and Northern Europe). Our jaws are getting progressively smaller (which is why some people have to remove their wisdom teeth to maintain a straight smile - and some people don't have wisdom teeth at all), some muscles are disappearing (the Palmaris Longus is one example - it's present in about 80% of humans), and other subtle changes are occurring.

Just don't make the mistake of equating "evolved" with "superior." Evolution is dictated by the ever-changing demands of the environments we find ourselves in, and what's beneficial today isn't guaranteed to be beneficial forever.

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Thank you, but let me understand you. You are saying that yes, there had to be a discrete point in history, where the first homo-sapien, was literally, born to parents who were not homo-sapiens? 1) What species were those pre-homo-sapien parents? 2) Was there just one instance of this first-homo-sapien being born? A figurative 'Adam'? Or were there multiple first-homo-sapiens being born at around the same time to different parents throughout the tribes/groups etc? 3) If (2) is true, why/how the sudden convergence of many homo-sapiens being born at the same time? –  Mohammad Aug 24 '12 at 15:30
    
4) Are you also saying that even though those first-homo-sapien(s) were in face human and their parents were not, they most likely didnt act that different from their parents? In that, they had the capacity for everything we take humans for granted today, but this capacity was never used? 5) Silly question but I have to know, if they were humans and their parents were not, how did they look relative to their parents? If their parents were not human, but the offspring was... wouldnt their parents be hairy apes and the offspring not so hairy humans? Not being facetious, serious question! :-) –  Mohammad Aug 24 '12 at 15:33
    
Don't want to be pedantic but Homo Sapiens is singular, no need to take off the s when talking about one (also because that is not the way plurals work in Latin). On a separate note, you may want to have a look at the Wikipedia pages for Mithochondrial Eve and Y-chromosomal Adam –  nico Aug 24 '12 at 15:34
    
1) It's hard to know for sure. It doesn't help early humans interbred with other close cousins, like Denisovans. The species prior to Homo sapiens (thanks Nico) may have only existed for a very short time and may not have left any records. 2) Probably, as genetic mutations are passed linearly from parent to child. However, the mutations could occur twice, though it is unlikely. As Nico points out, we have, indeed, found a "Mitochondrial Eve". 3) They weren't born all at once. The population most likely gained numbers steadily over generations. Humans generally follow exponential growth. –  MCM Aug 24 '12 at 17:09
    
4) They probably acted like their parents because that's all they knew how to do. The capacity for creative problem solving probably came in handy, which is why they lived long enough to reproduce. However, it was probably later humans which really got the ball rolling is what I meant. 5) Probably pretty close, again. You're assuming, however, the parents were more ape-like than human-like, which wasn't the case. You would probably mistake them for humans if they were alive today! While apes are our closest living cousins, there's still MILLIONS of years of divergence. Lots of time for change! –  MCM Aug 24 '12 at 17:16
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but I get lost on the 'border' cases.

Not surprisingly, since there are no borders, and this is probably the greatest misunderstanding: Evolution is gradual. It’s not generally possible to say where a complex feature (or a species) starts and another one ends. We could in theory say, for individual mutations on the genetic level, in which generation they first occurred, or when they became fixed in the population. But we cannot infer from these atomic changes where our ancestors started becoming humans. So the whole concept of “first human” is not biologically meaningful.

The best analogy remains a gradient between two colours. Going from the left, where does blue end and red start?

Colour gradient

By the way, you spotted this very well by yourself:

[if there is no first human] then that necessarily means that the definition of a species is itself fuzzy

Exactly, that’s the case. For more details on definitions of species, refer to MCM’s answer. But it’s indeed crucial to note that the definition of species (or any other biological classification) is an ever-changing approximation which tries to fit a definitive yes/no answer onto a gradually changing scale.

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Hmm, interesting... but then let me pose the question in a different way... what distance between any two colors on this scale, when mated together, cannot give an offspring that can then reproduce?...Do you see what I am asking? What is this minimal distance? Perhaps this is then the true measure of 'specieness'. –  Mohammad Aug 24 '12 at 19:08
    
There's no hard-line rule for that either. There are a large number of genetic and developmental factors that influence reproductive viability. You can have two closely related "species" that actually can interbreed successfully one in a thousand times. You can also have two members of a single species population that can't successfully interbreed. How many species are represented by a lion, a tiger, and a fertile female liger? (en.wikipedia.org/wiki/Liger) –  Russell Borogove Aug 24 '12 at 19:22
    
@Mohammad Excellent question. Unfortunately, Russel’s answer is spot-on. For instance, some species of dogs cannot inter-breed simply because of size differences, not due to other genetic incompatibility. Some species of crickets could inter-breed but aren’t sexually attracted to each other due to different mating calls. Some species, such as the Larus gulls (technically, all one species) can both inter-breed with a third, but not with each other. –  Konrad Rudolph Aug 25 '12 at 10:14
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@Mohammad I had understood the question but the answer remains that 1. we do not know, and 2. it varies. Concerning your specific example, it’s not even known whether humans and chimpanzees (not ancestors, but closely related species) could produce viable offsprings. Many biologists are convinced that they could, even though their chromosome numbers are different. Of course, this is an impossible, because unethical, experiment. Mating modern humans with 250kya ancestors would almost certainly work. –  Konrad Rudolph Aug 25 '12 at 13:47
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@shigeta I’m uncertain – a single individual with a mutation does not a species make. That said, speciation can be fairly abrupt simply because (separated) subpopulations have to respond to sudden changes in environment. –  Konrad Rudolph Jan 28 '13 at 12:57
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While the definition of species certainly is fuzzy, the process of species generation is easily defined: migration of a population part leads to two geographically isolated gene pools which do not communicate genetic information. Both pools will, through genetic drift (mutations/inserts/deletions), develop away from each other to the point that, if they were to meet again, they could no longer produce offspring with each other. Voilà, a new species.

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The process of species generation, speciation, is most certainly not easily defined. It is still the subject of many a PhD thesis. The definition you offer is only relevant to sexual species. Most species on the planet do not have sexual reproduction. Also, many of those that do can interbreed with other species. Quite a few examples of this have already been mentioned in previous answers. –  terdon Aug 26 '12 at 15:29
    
Just one point: if species can interbreed with species, contrary to definitions of the speciation process, then it is plausible to hypothesize they weren't species to begin with. –  rwst Aug 26 '12 at 16:54
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I'd just like to expand on Konrad and MCM's answers. If I understand you correctly, your main question is "what were the 1st human's parents". You cannot really get an answer to that because the question itself is wrong.

The idea that evolution moves in discrete bounds, that is that speciation occurs suddenly, from one generation to the next (also known as Lamarckian evolution) has been abandoned years ago. That is simply not how evolution works (our modern knowledge of epigenetics notwithstanding). The color analogy given by Konrad is indeed a good one.

So, there was never an individual 'proto human'. This is also the case for all other species. What you do get, usually, is that a change in a species' environment (e.g. temperature, atmospheric pH, the introduction of a new predator etc) causes a particular mutation, or set of mutations, to become advantageous.

One has to remember that a genome (an organism's genetic material, their DNA) is not stable. It is in fact extremely dynamic and constantly undergoing mutational changes. Most of these mutations are neutral, they do not affect the organism in any way. However, when an external change such as I mentioned before occurs, some of these mutations may become advantageous.

Imagine a random mutation that causes an individual of a species to be more resistant to cold. If this occurs at the beginning of an ice age, that individual is more likely to reproduce, passing the mutation to its offspring. Over time, since the mutation-carriers are likelier to survive and reproduce, this mutation will spread across the population and become "fixed".

At some point these changes accumulate past a certain indefinable point and we call a speciation event. This does not occur at the individual but at the species level. A good analogy here is the sorites paradox. How many stones does it take to make a pile?

So, to sum up, humans did not evolve from monkeys. Humans and monkeys at some point shared a common ancestor. Then, over a long time period, successive changes caused the two species to diverge. That is not the same thing. The linear concept of evolution that has one species morphing into the next is one of the greatest misrepresentations of a scientific concept ever perpetrated by the media and inflicted upon the unsuspecting public.

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"[H]umans did not evolve from monkeys" - I strongly dislike this claim. There is no doubt in my mind that the common ancestor of humans and currently extant monkeys would be classified as a monkey so I think a more correct statement would be "humans did not evolve from any current living species of monkey". –  Jack Aidley Jan 28 '13 at 11:18
    
@jackaidley The point is that the hypothetical ancestor does not exist. Whether it would have been classified as a monkey or not is moot. Humans did not evolve from the animals we know today as monkeys. In any case, it is the construction that really bothers me. Species do not really evolve from one another. They evolve. The "from" implies a sense of linear progress that is simply wrong as explained by the various answers on this page. –  terdon Jan 29 '13 at 13:07
    
The hypothetical ancestor most certainly does exist. It's just not extant. Your point about "from" is a good one, but yet I don't see any sensible way to discuss the evolutionary history of species without without using it or a similar construct. –  Jack Aidley Jan 29 '13 at 13:48
    
@JackAidley I just tend to avoid using a preposition to get around it. And no, it does not exist. It has existed, but it does not exist today. Both exist (in the present tense) and extant mean that something is in existence at the moment. –  terdon Jan 29 '13 at 14:03
    
There seems little point arguing over the exact meaning of the words exist and extant, so I'll merely note my disagreement and leave it at that. As to the rest, how then do you convey the evolutionary history which is concisely described as "humans evolve from monkeys"? –  Jack Aidley Jan 29 '13 at 14:06
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There are a lot of good answers here, but let me try to streamline things a bit: @Konrad's analogy to the color spectrum is spot on - where does red begin in that spectrum? This is essentially your question - where in the continuum of generations does the Homo sapiens species begin?

Just like our definition of color is imprecise (we usually can identify bright red and deep blue, but we cannot be sure about the shades in between), our definition of species is imprecise. We can identify a modern human and we could identify a far ancestor as such, but if we were presented with somebody from an intermediate generation, we could not confidently say if they are Homo sapiens or not.

We could, arbitrarily, point to a particular individual and say it was the first human, but it would not have any scientific meaning.

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Lucas, thanks for your answer. Yes, I am trying to figure out, where the biological scientific community draws a discrete like in the sand and says anything less than this is not human, anything more is human. (I understand that it can be somewhat arbitrary, but surely there is an agreed upon threshold, if only so that not everyone makes their own arbitrary thresholds in the literature?). And what exactly do you call them? Humanish? 64%human? 12%human? How does it work in the literature? –  Mohammad Aug 25 '12 at 14:40
    
@Mohammad, I don't think this issue comes up for humans that often - after all our nearest species relative that is not extinct, is easy to tell apart from human, except maybe in a dark room :). As far as classifying prehistoric "missing links", giving them a percentage of "humanness" does not make any sense, since that would imply that we could accurately describe what a 100% human was and relate it to them. I suppose, if we suddenly discovered a remote populated island, whose inhabitants cannot reproduce with the rest of humanity, we might need to deal with that issue :) –  Lubo Antonov Aug 25 '12 at 14:49
    
Lucas, in other words, the actual physical lack of evidence from swaths of the spectrum (by virtue of extinction) has nicely delineated in a clear way what is a human, and what is not, and hasn't forced the issue onto the biological community. Fair enough, I suppose I can reluctantly accept that. :-) –  Mohammad Aug 25 '12 at 14:53
    
@Mohammad, yes, I think you make a good point. To use the color analogy again, if all we could see was blue, red and purple, we could point to purple and say "this is not red". –  Lubo Antonov Aug 25 '12 at 15:00
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Ernst Mayr, distinguished elder statesman of twentieth-century evolution, has blamed the delusion of discontinuity — under its philosophical name of Essentialism — as the main reason why evolutionary understanding came so late in human history. Plato, whose philosophy can be seen as the inspiration for Essentialism, believed that actual things are imperfect versions of an ideal archetype of their kind. Hanging somewhere in ideal space is an essential, perfect rabbit, which bears the same relation to a real rabbit as a mathematician’s perfect circle bears to a circle drawn in the dust. To this day many people are deeply imbued with the idea that sheep are sheep and goats are goats, and no species can ever give rise to another because to do so they’d have to change their ‘essence’. There is no such thing as essence.

enter image description here

The barrier would not come suddenly. There would never be a generation in which it made sense to say of an individual that he is Homo sapiens but his parents are Homo erectus. You can think of it as a paradox if you like, but there is no reason to think that any child was ever a member of a different species from its parents, even though the daisy chain of parents and children stretches back from humans to fish and beyond. Actually it isn’t paradoxical to anybody but a dyed-in-the-wool essentialist. It is no more paradoxical than the statement that there is never a moment when a growing child ceases to be short and becomes tall. Or a kettle ceases to be cold and becomes hot. The legal mind may find it necessary to impose a barrier between childhood and majority — the stroke of midnight on the eighteenth birthday, or whenever it is. But anyone can see that it is a (necessary for some purposes) fiction. If only more people could see that the same applies to when, say, a developing embryo becomes ‘human’.

The Ancestor’s Tale Richard Dawkins,

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This is quite fantastic! If only because images convey so easily what is so hard to convey in words! Thanks for this, it is clearer now. I will say however, that a legitimate aspect of confusion comes from the use of 'species' as a term. We cannot be told that there exist giraffes and men, and that we are of different species, only to then simultaneously be told that there is no border defining this difference of species we were originally informed about to begin with. –  Mohammad Aug 26 '12 at 14:22
    
"The ‘gap’ comes from hindsight. There was nothing resembling a gap at the time, and the ‘classes’ that we now recognise were no more separate, in those days, than two species. As we shall see again, jumping gaps is not what evolution does." –  apoz Aug 26 '12 at 15:35
    
Hi @apoz - this answer is considered useful by the community but still needs to consist of more than direct quotes. –  Rory M Nov 20 '12 at 0:48
    
@apoz great picture, perhaps it should read "this is how creationists think evolutionists think it happens" - creationists would have no arrows! –  GriffinEvo Feb 13 '13 at 16:57
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