When Did the First Human Appear on Earth?
like a natural question, right? My parents are human...
and my grandparents are also human... and my grandparents’
parents are human, too... But if we go back in time like
this, when does the chain of our ancestors end? If we
were created, as for example the Bible says, then of
course the chain ends at our creation point. But suppose
for a moment that we were not created at a point in time
as the Bible tells us, but evolved rather gradually, as
science tells us — then what? The chain can’t go
backwards forever, because we know there were no human
beings, for example, 1 million years ago.(1) So?
Doesn’t there have to be a First Human even in the case
of evolution, a pair perhaps — an “Adam” and an “Eve”
— who became the progenitors of our kind? Doesn’t the
biblical story have to be true anyway?
Some readers who have read this other page of mine, on the origins of life, have contacted me asking the above question. In that page I state that there was no first living being, and I try to explain why. Nonetheless, some readers disagree, and argue for the creation of the First Human even under the assumption of evolution, as I just explained in the previous paragraph. They see the conclusion as necessarily following by common sense and pure logic. I would like to show in the present page how it can be logically possible that there was no First Human. The reasoning is simple, but we need an analogy to make it easier to understand.
Let’s think about something related: the evolution of a language instead of the evolution of humans. Let’s use a particular language as an example: the evolution of Greek, from the ancient, to the modern language. (Don’t worry, you don’t need to know a single word of that language to understand this analogy, guaranteed! ) I’ll tell you how Greek evolved from ancient to modern, without ever having a “first modern Greek speaker”. What we’ll learn about Greek is true for every other language that evolved from an older to a later stage (including English, for example), but I prefer Greek because I am more familiar with the evolution facts of that language, and so I will not make false statements. But the point is that, not only it doesn’t matter which language we use as example, but also the analogy carries over to what we are interested at: just as there was no first speaker of a modern language, there was no First Human either. And the analogy is true even in some of its details! Let’s see first what happened to speakers of Greek.
|Look at the figure above. Time runs from left to
right. The green color is the time when
speakers of Greek were speaking the ancient language, and
the blue color is for speakers of the modern language.
Underneath the colored band I drew a large number of very
short vertical lines, each of which is supposed to
represent one individual. A single line is one person,
and the line to its left is one of this person’s
parents, whereas the line to its right is one of this
person’s children. There should be many more lines,
actually, but there is not enough horizontal space to
make the drawing realistic. (Other things are not
realistic either, such as the lengths of the ancient and
modern stages — but realism is not necessary here.)
Now, let’s see what we have. Each person’s “color” corresponds to the particular version of Greek that the person was speaking. The difference between colors shows how different the versions were. For example, “very green” means “typical ancient Greek”, and “very blue” means “typical modern Greek”. Somewhere in-between there is a region where the language changes. The change is smooth, but also somewhat sudden, if we look at the overall picture. Indeed, since around 300 BC, after Alexander’s death (that’s Alexander III the Great, king of Macedon), until around a couple of centuries after Christ, the change was complete. The historical reasons for the change do not concern us here.(2) What concerns us is the color. Notice this property of the color:
But now look what happens if we take an ancestor-descendant pair that do not have an immediate parent-child relationship. How much they could understand each other (if they had lived at the same time) depends on how much they differ in color; not on how distant they were in time. For example, we can take two ancient people, both in the very green area on the left, but differing by several centuries from each other — let’s say 800 years. These two people would understand each other, if they could somehow miraculously be brought together. But if we take a pair where the ancestor is from around 300 BC, and the descendant from around 200 AD (making a difference of 500 years), these two people would not be able to communicate (or, in reality, the communication would be extremely limited).
Is there any point in time that we can single out and say, “There! That’s when the first speaker of modern Greek appeared”? Of course not. There is a smooth change, not an abrupt appearance of the first modern Greek speaker. But even though every parent can communicate with their children (and with their grandchildren, clearly), still, the change within those centuries is such that the ancient speaker would not be able to communicate with the modern one, if they could be brought together in time.
Exactly the same idea can be carried over to the notion of change from our ancestor species Homo erectus (that corresponds to “ancient Greek”) to our own species, Homo sapiens (that corresponds to “modern Greek”). Let’s take a look at the following figure.
|Is anything different between this figure and the previous? Not really. Only the terms have been changed. And the important points in our analogy are the following:|
was previously language, now corresponds to the
DNA of an individual;
|So, if we take any two individuals
from among “our kind”, Homo sapiens, which
is the clear red region, no matter how distant in time,
these two individuals would be able to produce fertile
children after mating (assuming they were a man and a
woman), because their DNA’s would be sufficiently
similar. The same thing would happen if we took two
individuals of our ancestor species, Homo erectus, from
the clear magenta region in the figure. Again, the DNA’s
of these two individuals, no matter how distant in time,
would be sufficiently similar to allow the birth of
fertile children. That’s why we say these two belong to
the same species, H. erectus, and those two
belong to another species, H. sapiens. But if we
take one “purple” and one “red” individual, their
DNA’s would be different enough to not allow
fertile children to be born. It could be that the chances
to succeed in having a healthy child would be nearly zero
(say, one in a million). Or, that sometimes children
would be born, but those children would be unable to have
children of their own, so they would be sterile, “dead
ends” as far as propagation of genes is concerned.
Nonetheless, the magenta region does not change sharply to red, but gradually. There is never any “First Red” individual. If we take any two opposite-sex individuals that belong to succesive generations (but not to the same family obviously, avoiding incest), these two individuals (one from the parent’s generation and the other from the child’s generation) would be able to mate and produce fertile children. They would belong to the “same kind”, even if they were taken from the transitional time of around 200,000 to 150,000 years ago, because their DNA’s would be sufficiently close.
How do we know all this? How sure are scientists that the above is true? Have we ever examined the DNA of a H. erectus, and compared it with the DNA of a modern human?
No, no one has retrieved DNA from fossil bones as old as those of H. erectus. The oldest DNA that has been retrieved at the time this text was written (ca. 2005) is a few tens of thousand years old. But paleoanthropologists (scientists who study the origins of the human kind) examine fossils, and are experienced enough to tell with some confidence when a skeleton should belong to one species, and when to another. In reality, we will be nearly 100% certain only when we obtain the DNA of a H. erectus individual, and this will take time, because the older the fossil the more improbable it is that the DNA has been preserved somewhere. But it is not impossible to find it, somewhere on this planet. Perhaps deep frozen under the vast unexplored ice sheets of Siberia (if H. erectus ever reached there).
But suppose that we find such a DNA molecule, and after we compare it with a modern DNA molecule we realize — to our surprise — that in fact the two DNA’s are similar enough to qualify as “same species”: the two individuals would in principle be able to have fertile children after mating. Would this discovery demolish the explanation presented in the previous paragraphs, about the nonexistence of a “First Human”?
Not at all. Such a discovery would simply push the species-distinction era further back in time. All right, so it would not be what we call H. erectus the species of which we would have the honor to be the descendants. We would be the same species with them, in that case. So? There would be another species, further back in time, that would have sufficiently different DNA to disallow mating and production of offspring with “us”. But still the change between that species and the erectus-sapiens species would be gradual-and-yet-abrupt, as the figure with the magenta and red colors depicts it. And so, still there would be no “First Human”.
This notion of “gradual-and-yet-abrupt” change, by the way, is a hard one to grasp, because the words sound self-contradictory: is it gradual, or is it abrupt? But I think the colored figures, above, depict in a nice way how the change can be both gradual and abrupt, without any contradiction:
Naturally, the previous discussion is true for any two species that have an immediate ancestor-descendant relationship; it is not confined to the human ancestry case.
|Though not relevant to the “First
Human” question, for the benefit of some readers who
objected to the above, I feel I should also mention the
following related issues.
Some people feel uncomfortable when reading these things. One (unfortunately still common) reaction is: “But does that mean we evolved from the chimpanzees?”
In truth, there is something special between us and chimps. It is that of all living beings on Earth, chimps have a DNA structure which is most similar to ours. This is a hard fact, like “the Earth is round”; it cannot be disputed: you take the chimp-DNA molecule in the lab (an average of some living individuals), and the modern human DNA (again, an average), you compare them, and find some differences. If you do this with any other living being on Earth, you’ll find that the chimp DNA has the fewest differences from our DNA. That’s all that there is to it. And that’s why we look more similar to chimps than to rhinos.
And if you continue your DNA-explorations, you’ll find that the next-most-similar DNA to ours after the chimp (the two species of chimps, actually: the common and the bonobo), is the one of the gorilla. And after the gorilla follows the orangutan. And then the gibbon, the “lesser ape”. And then, more distant, are the DNA’s of monkeys and other primates. But still, all these DNA’s are closer to our DNA than, say, the elephant’s DNA.
All these are indisputable facts. And the theory of evolution explains these facts. It says, for example, that our common ancestor with the chimps lived more recently than our common ancestor with the gorilla. It is as if we are first cousins with the chimps, but second cousins with the gorillas (and third cousins with the orangutans, and so on). If some readers feel shame that we have such relatives, I would say, I feel more proud of being related to the peaceful bonobo chimps, rather than to some people such as Hitler and Pol Pot. What about you?
|Opinions expressed by
readers after reading this page
A reader from a discussion group wrote the following (in their forum, the full text can be found here):
The above reader’s view is wrong on a couple of counts:
1. I don’t attempt to “prove” anything with this analogy. Firstly, real proofs do not exist in any domain other than mathematics. Every use of the word “proof” elsewhere is sloppy. But setting sloppy language aside, and replacing “he proves” (in the first quoted paragraph, above) by “he brings evidence for”, even this idea is wrong: I don’t attempt to bring evidence for anything. An analogy does not bring evidence; it simply invites the mind to remove its blinders and expand its horizon by making a mapping between an unfamiliar idea or situation, and a hopefully more familiar one. An analogy is a thinking aid, not a proving tool.
2. The above reader’s main point is that mine is a “false analogy”, because there is a barrier (I adopt his terminology) between species (e.g., a cat cannot become a dog, and vice versa), whereas there is no such barrier between speakers of languages such as ancient and modern Greek. This idea is wrong for two reasons:
2a. It is not true that speakers can switch between languages such as ancient and modern Greek. I am talking about native speakers.(3) Ancient Greek, as we all know, is a dead language, meaning that there is no native speaker of it alive today. A dead language cannot be revived: we cannot have native speakers of ancient Greek today, no matter which way we try. For to have a native speaker a community of other native speakers is required, and an individual must grow up in that community from a very early age. (There is a “window of opportunity”, well-known in developmental linguistics, available to every mentally normal child, that appears from birth to the early teenage years; a child who is not exposed to a given language during this window of opportunity cannot become a native speaker of that language.) Given that there is no community of speakers speaking ancient Greek, it follows that we cannot have a native speaker of ancient Greek in our times.(4)
2b.Even if the above point (2a) were not true, i.e., even if there were really no barrier between ancient and modern Greek, one must have a sense of which features of an analogy are essential, and which are irrelevant. An analogy is not an isomorphism, forcing every detail to be identical between the two mapped structures. For example, the DNA is propagated by sexual reproduction (at least in the cases of species concerning us here), so a female and a male individual are required; but there is nothing analogous to sexual reproduction in language. On the other hand, a language has a mandatory spoken form and an optional written one, but there is nothing analogous to this in the DNA case. Also, language speakers can be bilinguals or even trilinguals, etc., i.e., native speakers of more than one language, if they grow up in suitable multi-language-speaking environments; but living beings cannot belong to more than one species. All these differences (as well as the purported one suggested by the reader) are irrelevant for the analogy, the essence of which is that just as one does not need to postulate a single initial speaker of a language, so one does not need to postulate a single (or a couple of, male and female) initial ancestor(s) of a species. (Again, this is not a “proof”, or evidence for anything; it is simply a suggestion that it is logically possible to not have a single individual, or couple, as the progenitor of an entire species.)
Other opinions, expressed either in public or in private (by email to me) will be answered here, if in my view they raise some interesting point. The privacy of the opinion holder is guaranteed upon request.
Footnotes (clicking on the number brings back to the text)
1. How do we know this? Because no fossil skeleton or single bone of our kind, Homo sapiens, has been found that is older than around 200,000 years ago.
2. But in case you do happen to be interested in the historical reasons, they are related to Alexander’s conquests. In the centuries after his death, a lot of people in Asia and N. Africa learned to speak Greek. So did the educated among the Romans. Thus, Greek became a “lingua franca”, the international language of those times. However, because it started being spoken not only by native Greeks, but also by “barbarians” (as the Greeks were calling all non-Greeks, but not in the modern derogatory sense), the Greek language was “eroded”. This phenomenon has been repeated many times in history — take, for instance, English and its difference between its modern varieties and the English of Chaucer’s time (1340?-1400). Also, contrary to the modern era, in the ancient times there was no television or radio so as to standardize Greek and let one dialect prevail (e.g., the Attic dialect). Today the so-called “common American” is heard and understood throughout the English-speaking world, thanks to Hollywood and TV series. Back then, however, neither Athens nor any other Greek city had such privileges, so the rest of the Greek speakers eventually brought about the changes that led to the Greek language of the Byzantine times, which are easily understood by modern speakers of Greek.
3. Why the analogy works with native speakers only? Because languages are determined largely by the utterances produced by their native speakers. Non-native speakers can induce changes in a language and cause it to evolve in a catalyst-like fashion, as footnote 2 explains, but they do not determine what the language is. If we include, for example, my ungrammatical Italian as part of the Italian language (because I happen to know a few Italian words and can surmise about how to put them together), and we do this for every non-native speaker of Italian, then the Italian language will lose its character; it will cease to be what it is — it will hardly be recognized as Italian.
4. The following thought experiment is possible, however: a number of ancient Greek aficionados gather in a place and form a community. They all know ancient Greek as a second language, i.e., they are not native speakers of it. But they all live in the same locality, marry only with members of their community, and raise their children by speaking to them whatever ancient Greek they know. Modern linguistic theory then predicts that the children raised in this way will become native speakers of ancient Greek (or a close approximation thereof), automatically correcting the non-native errors of their parents. (We have to assume that the parents are very good non-native speakers, otherwise the children might converge to a language that differs substantially from true ancient Greek.) Examples of such a situation come from communities speaking pidgin languages, where children raised within such communities became native speakers of creolized languages.
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