As mentioned in earlier sections, much about human lineage is unknown; even more is the subject of intense debate among anthropologists. Much of the disagreement is due to an incomplete fossil record; only new discoveries will answer those questions. Another significant factor is the lack of accurate dating methodology; the best methods have only been recently developed. Finally, the study of human evolution did not really begin in earnest until the mid 1950s, when australopithecus Africanus was accepted--it is a very young discipline. Time may well be the determining factor as advances in methodology and technology yield more and more answers.
Whatever the reason, many of the questions are being answered as you read this by anthropologists, paleontologists, and other researchers in the field. It could take decades to find the answers. Who knows, maybe you will find the key to unlock the secrets of human evolution!
The Australopithecine Quandary
We have taken a look at four species of australopithecus, but, upon closer inspection we can see as many questions as answers. For example: afarensis is the oldest; it has a primitive, ape-like face and modern, human-like legs. Africanus is the youngest (and presumed to be most evolved of the species) and it has a modern, human-like face, but primitive, ape-like legs. Modern legs denote bipedal movement and are considered and important evolutionary step, yet the more "modern" of the species has one of the more primitive leg structures. Determining how physical characteristics evolved would shed a great deal of light on our past; australopithecus seems to contradict current presumptions.
And then there is garhi. With an ape-like face and modern, human-like legs and teeth, garhi seems to share characteristics with both afarensis and early forms of homo. EARLY FORMS OF HOMO???? Yes. Garhi has almost as much in common with modern humans as does Africanus. Does this mean that garhi is really our direct ancestor? Does Africanus represent a line that eventually went extinct?
These questions are important as they could indicate which australopithecine (if any) led to modern humans. A recent re-examination of the Sterkfontein (South Africa) fossils suggests that africanus is as young as 2-2.5 million years old--a far cry from the previous estimate of 2.5-3.5 million years old. If true, it could place garhi as the immediate predecessor to africanus.
One Big Happy Family?
Swartkrans (South Africa) provided the first evidence that two early hominids (homo erectus and paranthropus robustus) lived in the same region at or around the same time. Since then, several sites have yielded fossils indicating that more than one of our ancestors existed at the same time in the same place. While this may not be a surprise to the layperson (it seemed logical to the author: if you have many breeds of dogs, why not many breeds of hominids?), to the scientific community, this is revolutionary.
Scientists were of the belief that hominids developed in a relatively linear fashion--one species evolving into another with little overlap. The discovery of multiple, contemporaneous species suggests a "shot-gun" approach to evolution: throw several species into the mix and add some anatomical differences; some will hit (survive), some will miss (become extinct). To quote a popular expression: "you have to break a few eggs to make an omelet."
This discovery also begs the question: if multiple species lived simultaneously, how did they interact? Virtually every theory has been advanced--from peaceful co-existence, to interbreeding, to open warfare. There is still no general agreement. Understanding this is crucial to our understanding of early hominid behavior.
Out of Africa...
Where did modern humans first appear and how did we populate the globe? Early evidence suggested Asia or Europe. Recent discoveries in Africa, however, have changed everything. Now there are two leading theories.
The first, or "Out of Africa" holds that small groups of modern humans migrated from Africa into the rest of world. The migrations may have been instigated by environmental changes (natural or man-made) and occurred in various waves between 50,000 and 125,000 years ago. Proponents of this theory point out that DNA evidence suggests a common ancestor for all humans that lived anywhere from 120,000 to 220,000 years ago. In addition, the oldest known modern human fossil (130,000 years) was discovered in South Africa.
Makapan's Valley (South Africa)
australopithecus africanus fossil site
...or Out of Time?
This theory, popularly called the "Multi-regional Theory", argues that evolution is an inevitable result of time. Small populations of early hominids naturally evolved into modern humans at multiple locations around the planet.
Supporters of this theory point to anatomical evidence showing physical similarities between modern humans and early humans found in the same region. There may be some truth in both theories, but this will continue to be a controversial topic for quite some time.