SPEAKER: A useful model that paleoanthropologists use to show the relationship between fossils is called the phylogenetic tree. How do you construct a phylogenetic tree? In looking at fossil material, one of the most obvious features are morphological differences, not just body size but also changes in the structures of the skull and also of the bones below the skull, the postcranial skeleton. So morphology is a very important key.
But today we're moving into some new and exciting areas which assist in our phylogeny. And that is looking at biochemical variables between the living apes and monkeys and seeing the degrees of difference between them, which allow us to construct another type of phylogenetic tree. And also DNA analysis is just coming on the horizon, which will certainly be very useful in helping us understand degrees of genetic relationship.
Charles Darwin was probably right in his hypothesis that the ancestors of humans came out of Africa. And that was because the chimpanzee and the gorilla were there. And he knew about them. And he realized that they showed more characteristics of a human nature than the Southeast Asian orangutan and the gibbon. However, we must remember that our ancestors are not chimpanzees and gorillas. They too have their fossil record. They too have fossils that are yet to be discovered and will probably go back into that period of the middle Pliocene when a separation occurred between humans and apes.
Phylogenetic trees are drawn by different people in different ways because of their interpretations of the fossil record. But there are broad features of the phylogenetic tree upon which there's general agreement. One of these is that ardipithecus, at the moment, is the earliest known fossil of the human family, dating to 4.4 million years ago. This was in the Pliocene Epoch.
And from that period into the early Pleistocene Epoch, we see the emergence of a number of hominids that we assign to the general category Australopithecus or australopithecines. We did not know anything about these early hominids until 1924 when a discovery was made in South Africa. In the 1930s, adult forms and many more forms of australopithecines were found also in South Africa and then at later times in East Africa and North Africa as well.
What's interesting about the australopithecines is that they don't fit into the meiocene ape patterns at all but show some very unusual characteristics. But we recognize them as nonetheless within the human family. For example, they're bipedal. They move on their hind legs. They may have spent some time in the trees using hind legs for movement, particularly for escaping predators and also for foraging in the forest, but they were able to walk on their hind legs rather than walking on their forelimbs as quadrupeds are wont to do, as horses, cows, kitty cats, and dogs, as you can see, all use forelimbs. We have evolved two limbs. And like the other apes, we do not have tails.
Also, by evolving lower limbs adapted to movement, to locomotion, the feet have lost most of their grasping qualities or prehensile qualities. And grasping with the hands and the feet is very characteristic of the other primates. It is not a characteristic for ourselves except for manual prehension. We have essentially lost our prehension for the feet. Another character is that the brain is larger, again, in relationship to the total size of the body.
The canine teeth have decreased in size. And if you look at the canine teeth of, say, a baboon or a rhesus monkey, you'll notice that not only is it large but it's also projecting beyond the level of the other teeth. But you look in the mirror at your own teeth, and unless there's something remarkable going on, you'll notice that your canine teeth are at the same level as the other teeth adjacent to them. We have lost the projecting canine tooth.
We also have developed a more complex social relationship. We can't reconstruct social hierarchies in the past in the same way that we can with living primates. But the success of these early hominids in survival certainly must have depended to a large extent upon their ability to work in groups and bands.
How did they live? Well, I think they spent a lot of time in the trees, far more than we expect, even though we can call them bipedal two footed creatures. I think too that they were meat eaters. But in the earlier days of their evolution, their meat eating was based mainly upon what they could scavenge rather than what they could hunt. But hunting of small game may have occurred. And we know that chimpanzees and rhesus monkeys today do undergo hunting patterns. So it's not surprising that some hunting may have occurred. But meat eating certainly becomes a more frequent pattern in this group of australopithecines.
Another thing that I would like to tell you about this group of early Pleistocene hominids is that they came in many different varieties and kinds. They were not all alike. Some were rather gracile, not very tall, probably not reaching more than 3 and 1/2 and 4 feet. Others were quite large, within the range of modern gorillas.
Because of these size differences, changes in the cusp patterns of the teeth, morphological features of the skull, degrees of robusticity, and a number of other anatomical variables, we have organized these australopithecines into several different species. The first one that was found in 1924 has been assigned to the species africanus so we call it Australopithecus africanus. But by the '30s, it was recognized that there were larger species more robust so they were called Australopithecus robustus.
And then in East Africa, found in the 1960s or late 1950s, was a hyper-robust form that has been called Australopithecus boisei. And this is not the end of the story. There are other forms that have been given different species names. So when we're talking about australopithecines, we can say, yes, they're all coming from Africa. The major finds have been made in South Africa and East Africa. Nonetheless, they were adapted to different environments and probably having very different dietary practices, as represented in changes in their dentition.
Are these australopithecines our direct ancestors? Well, yes and no. They certainly fill the temporal and spatial hiatus between the Meiocene apes and ardipithecus and later hominids. On the other hand, they do not show some of the features that we find in a specimen that was discovered in 1960, which was recognized as the first fossil example of a member of our own genus, not Australopithecus but the genus Homo.
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Since the time of separation of the evolutionary lines of apes and humans about 5 million years ago, some fossil specimens of the skeletal remains of our earliest ancestors have been preserved and discovered. Putting together the pieces of the puzzle of human biological history is the task of paleontologists, geologists and anthropologists.
In this room we explore how these scientists can reconstruct the past from their studies of the geological contexts in which fossils are found, the dating of the specimens, their comparative anatomy with extinct and living species of our taxonomic order, the Primates, and the lifeways and behavior patterns of the first members of the human family within the Primates.
By looking at reproductions and pictures of this fossil record, including representations of pre-human Primate species, we learn about our prehistoric beginnings among those populations of first two million years of our evolution, as identified as Ardipithecus, Australopithecus and the earliest members assigned to our own genus- Homo habilis and Homo rudolfensis.
This video is part 12 of 13 in the Human Paleontology series.