Where did we come from? Paleoanthropologists claim that the modern humans called Homo Sapiens branched out about 2.5 million years ago from australopithecus. By tracing mother-side mitochondrial gene, they also claim that the modern humans came out of Africa (Out Of Africa (OOA) theory) about 100,000 years ago. Did we really come from apes? Anatomically, there exist big differences between the modern humans and other hominins such as craniodental features, skeletal morphology, and especially the brain size. In the previous section, we saw that a major change for the Galapagos finches during 2 million years is just the shape of beak. So, it's hard to believe that the australopithecus was so much evolved to become human during such a short period of time of just 2.5 million years.
Figure 9. Did we evolved from apes?
This problem can be investigated further if we compare DNA sequences between the human and australopithecus. The mapping of human DNA was completed in 2003, but we do not have DNA information for the australopithecus. Let's assume that the DNA of the australopithecus is similar to humans closest relative chimpanzee. Scientists found that the difference of DNA between the human and chimpanzee is about 1.2%.
A new study found that when parents pass their genes down to their children, an average of 60 errors are introduced to the genetic code in the process. Sixty mutations may sound like a lot, but it is only one new mutation in every 100 million letters of human DNA. If we assume a single generation of australopithecus is 25 years, then it will be 100 thousands of generations of evolution from australopithecus to human during 2.5 million years. During this period, the total number of mutation in DNA during is only 0.1% (100 thousands of generations x 100 millionth). This number is just the same as average difference in DNA between individual humans today and less than 10% of DNA mutations required to evolve from australopithecus to human. In the calculation, we have assumed that the DNA mutations occur beneficially to the subsequent generation, but if they occur harmfully, it will never be possible to evolve from australopithecus to human in 2.5 million years.