Human Evolution
Timeline
Somewhere roughly 6 to 12 million years ago, the hominids, ancestors of humans, split off the evolutionary tree from the precursors of modern chimpanzees, our closest genetic relatives. Humans and chimpanzees share between 94% and 98% of our genetic makeup depending on how you measure, and are so similar that we share susceptibility or immunity to almost all diseases. Our hominid ancestors lived in Africa, and continued to evolve through the generations. Many theories conjecture that the loss of body hair and the upright posture of later hominids was an evolutionary response to life on or near the hot savanna of southern Africa. Both changes would serve to keep the hominid cooler, and the posture might also give an advantage in seeing predators or prey.
One of the more successful early hominids, Australopithecus, arrived about 4 million years ago. Roughly 2.5 million years ago, the first hominids known as Homo split off from the Australopithecus group. Their descendants, Homo habilis and Homo rudolfensis, began using stone tools. From the Homo rudolfensis line hominids became progressively smarter, and by about 1 million years ago they started using fire. They spread out geographically from Africa to Europe and Asia. Several groups of hominids coexisted and possibly competed against each other for resources. They continued to evolve, as shown by the extensive fossil record.
Around 195,000 years ago, we find in Africa the first fossils of Homo sapiens, the earliest human beings. The earliest “modern” human beings, or Homo sapiens sapiens, arrived approximately 150,000 to 130,000 years ago, and migrated out of Africa about 100,000 years ago. Homo sapiens sapiens evolved from earlier hominids, but did not eliminate all other evolutionary cousins right away. Populations of other hominids continued to exist for some time, and some of them evolved to give us the squat muscular Homo neanderthalensis (Neanderthal Man) in Europe and the tiny Homo floresiensis (Flores Man) in Indonesia, both intelligent species who survived until Homo sapiens sapiens eventually won out through evolutionary success. By around 50,000 years ago, Homo sapiens sapiens had spread out from Africa and Asia to inhabit Europe and Australia, and 20,000 years later some migrated from Siberia to Alaska, and then down to inhabit North and South America. The last Neanderthals held out until about 27,000 years ago. The last Flores Man died out sometime in the last 20,000 years, possibly as recently as the last several hundred years.
In the last 30,000 or 40,000 years, man began drawing pictures. Around 15,000 to 10,000 years ago, man discovered agriculture and began domesticating animals. With a more plentiful source of food, man had more time to devote to intellectual pursuits, and developed writing, with symbols standing for sounds. Some of the earlier forms of writing (from about 6,000 years ago) in the form of markings called “cuneiform” on clay tablets have been found and studied. With the advent of writing begins the recorded history of mankind.
This is the history of the evolution of man, from the split of hominids from chimpanzees until the beginning of written accounts of historical events. Remember, this chapter is a rough outline of the steps involved in our arrival here at this day and this time. Unlike in a traditional religious tome, the timeline above is based on theories and on interpretations of evidence, which may evolve and change as more evidence to back them up or break them down come to light. But the basic theoretical themes of human evolution have been shown valid again and again, with only adjustments in minor details. Below, we will present some of the major pieces of evidence for the evolution of man from other primates.
Theory & Evidence
Beyond the obvious physical and functional similarities between humans and other primates, there exists substantial evidence for the descent of man from earlier great apes. There are really two primary sources of this evidence: the extensive fossil record, and the biological and genetic similarities between humans and other primates.
Specific Fossil Evidence for the Descent of Man from Apes
Even with the incredible amount of developmental similarity and obvious common structures between man and other primates, some still dispute our lineage. They claim there are gaps in the fossil record, and say, “where’s the missing link?” In the fossil record, there are indeed two spots that are a bit sparser. Between the Australopithecus specimens—advanced but still somewhat “ape-like” precursors to humans that appeared around 4 million years ago—and the earliest fossils of Homo erectus and Homo heidelbergensis there was a gap of about a million years. And before Australopithecus Afarensis (one of the earliest Australopithecus fossil specimens), which dates back to about 4 million years ago, there’s a fossil gap of about 3 million years before we get back to the estimated time when hominids split off from chimpanzees. Where are the missing links?
Again, we’re being misled by arguments that are nearly a hundred years old. Since the 1960s, we have found fossil evidence for Homo rudolfensis and Homo habilis, two of the earliest groups to split off from Australopithecus. The first of those is closer to a direct ancestor of modern humans, while the second is likely a cousin on the family tree. (There is also some fossil evidence in the much-shorter gap between those two and Australopithecus, although scientists are still debating the analysis.) And after Homo rudolfensis, we now have fossil specimens of Homo ergaster and Homo antecessor, both likely near the ancestor line to Homo heidelbergensis (a later hominid) and Homo sapiens, human beings. There isn’t one individual specimen in the more recent “missing-link” gap, there’s over forty.
Even more recently, since the 1990s we have found ancient, more ape-like hominid ancestors in the gap between chimpanzees and Australopithecus. Ardipithecus ramidus, also called Australopithecus ramidus, was first described in 1994. The species, which lived approximately 4.5 million years ago, in many ways resembled chimpanzees. More recently, since 1997 there have been discoveries of older fossils in the gap between Ardipithecus ramidus and our common ancestor with chimpanzees, including four distinct species near our likely ancestor line, plus another older specimen near the point where humans and chimpanzees split from the other great apes.
So let’s give a timeline of some of the fossil evidence for human evolution from a common ancestor with chimpanzees. Again, there is still some debate over whether specific fossils are along the ancestor line or are merely cousins on the family tree. There is also debate as to where to draw the exact line between various species, since such lines by nature are quite fuzzy, and within any population there is a significant amount of variability between individuals. But we will show below the most common scientific namings for the various fossils, along with the discovery dates and the numbers of specimens found. For clarity regarding the old “missing link” arguments, we will show where the old gaps were as of 1925, the year of the famous Scopes Monkey Trial in Tennessee.
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Specimens found by 2006 |
Specimens found by 1925 |
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Older specimens
Pierolapithecus catalaunicus – 13 mya (million years ago) |
Older specimens
*None found - early gap |
|
Samburupithecus – 9.5 mya |
*None found - early gap |
|
Sahelanthropus tchadensis – 7 to 6 mya |
*None found - early gap |
|
Orrorin tugenensis – 6 mya |
*None found - early gap |
|
Genus Ardipithecus
Ardipithecus kadabba – 5.8 to 5.2 mya |
Genus Ardipithecus *None found - early gap |
|
Ardipithecus ramidus – 4.4 mya |
*None found - early gap |
|
Genus Australopithecus
Australopithecus anamensis – 4.2 to 3.9 mya |
Genus Australopithecus *None found - early gap |
|
Australopithecus afarensis – 3.9 to 3.0 mya |
*None found - early gap |
|
Australopithecus africanus – 3.3 to 2.3 mya |
Australopithecus africanus |
|
Genus Homo
Homo rudolfensis – 2.5 to 1.8 mya |
Genus Homo
*None found - later gap |
|
Homo habilis – 2.4 to 1.5 mya |
*None found - later gap |
|
Homo ergaster – 2.4 to 1.5 mya |
*None found - later gap |
|
Homo erectus – 1.8 to 0.3 mya |
Homo erectus |
|
Homo antecessor – 780,000 ya |
*None found |
|
Homo heidelbergensis – 700,000 to 400,000 ya |
Homo heidelbergensis |
|
Homo neanderthalensis – 230,000 to 30,000 ya |
Homo neanderthalensis |
|
Homo floresiensis – 18,000 ya |
*None found |
|
Homo sapiens – 195,000 ya to present |
Homo sapiens |
So the biggest gaps in the fossil record have been filled. The record itself is a full history of the evolution of man from earlier primates, much more than creationists would have you believe. Although the exact details of human evolution are still under review, the overall theory is valid and may be regarded as scientific “fact.” Again, you have to go where the evidence leads you, and we have hundreds of fossils showing the evolution of man.
Biological and Genetic Evidence for the Descent of Man from Apes
Beyond fossil evidence, there is significant evidence that humans are related to other great apes in their biology and genetic makeup, more than even the evidence we previously covered in the Book of Biogenesis. Humans and the other 3 great ape species (chimpanzees, gorillas, and orangutans) have almost identical ability or inability to eat various foods—all need vitamin C (unlike most mammals), though humans and our closest relative the chimpanzee have a further enhancement allowing them to be much more carnivorous—and are susceptible to almost the exact same set of diseases. Both types of hemoglobin in humans, the substance that allows our blood to carry oxygen, are identical to that of our closest relative, the chimpanzees. Our next closest relative, gorillas, differ by only one amino acid on each of the two types of hemoglobin.
And our chromosomes show our common descent, too. Humans carry 23 chromosomal pairs, while the other three great ape species all carry 24. If we evolved from a common ancestor, we should find evidence that two of the ape chromosomes fused together to form one of our human chromosomes. That exact evidence is found on human chromosome number 2. We can find there markings from leftover “ends” from the old great ape chromosomes where the two connected. We can also find markings from the leftover centromere (the bend in the middle) from the one chromosome that had to lose the centromere when the two joined together. These are clear-as-day evidence of evolution in action, marked in every cell in our body!
Note that mismatched chromosome numbers in and of themselves do not directly prevent fertility, as some creationists might argue when presented with the impressive evidence found in human and ape chromosomes. There are present day cross-breeding species with different chromosome numbers. As always, we must grade our hypotheses against the evidence at hand.
Conclusion
The data supporting man’s descent from the apes is overwhelming and irrefutable. The biological and genetic evidence supporting evolution from a common ancestor with chimpanzees is so strong that denial of it is tantamount to an outright falsehood. The fossil record is quite extensive, and all supposed “gaps” have been filled in with recent discoveries. We have the proverbial “mountain” of evidence that turns a hypothesis into a theory so strong that it is a scientific fact. We can trace our evolution from apes to humans quite clearly, and see the steps in our development, era by era.
But remember, these steps in the evolution from more primitive hominids to modern man were usually not large, discrete steps. Yes, along the way there was the occasional highly beneficial mutation, but for the most part evolution, even along the line to modern man, is a great sliding continuum. Has there been human evolution in the last 10,000 years? Absolutely. The size or thickness of the jaw and teeth of humans from 10,000 years ago were approximately 10% larger than now. But a person from 10,000 years ago is certainly a member of our species, and would for the most part be indistinguishable from a modern human.
What about a human from 50,000 or 100,000 years ago? The genetic differences and surface differences and possibly behavioral differences would be much more pronounced, but such a person would still be Homo sapiens sapiens. How about 150,000 years ago? Now we’re reaching that fuzzy border of our specific species. If we raised an infant from that time in modern culture, there would likely be significant noticeable differences in features, behavior, and intelligence, although such a person could probably breed with a modern human. Such an effect is seen with the differences between dogs and wolves. But as we travel farther back, at some point we will reach an ancestor with which we would only likely breed sterile offspring (similar to how horses and donkeys breed only mules), and even farther back we would reach a level where crossbreeding is not possible. Once again, we emphasize that human evolution—indeed all evolution—is a long continuum of intermediate steps.
Much more detailed evidence on human evolution can be found in some of the titles offered in the Book of Books; we encourage those interested to read further from those highly-credentialed authors. And once again, we also list the Talk.Origins website (www.talkorigins.org/indexcc/) as a great source for tearing apart the false claims of creationists, and EvoWiki (www.evowiki.org) as an excellent source for detailed information on evolution in general, and specifically the history of the evolution of Homo sapiens sapiens. The descent of man from the apes is a fact, and not one we should shy away from. The wonders of evolution have fortunately brought the light of intelligence to humanity, so that today we can think and can write, and can even read books such as this one!
The Big Bang, evolution, and the descent of man from apes are all facts, proven again and again by a vast encyclopedia full of evidence. We have given just the tip of the iceberg of evidence here in this book; the actual details are far too many to be contained here, or in any single volume. To those who say “evolution is just a theory,” we must respond “creation is just a fairy tale.” As rational, reasoning adults, it is incumbent upon us to teach our children facts—and that includes undeniably proven, robust scientific theories—not myths and fairy tales.
