some of the biggest challenges to our survival.
Anthropocene A new planetary era in which humans have become the dominant force in shaping the earth’s physical make-up and processes
ACTIVITY
Visit your local natural history museum and explore the evidence of early human life. Make a note of the main differences between early humans and humans today. Learn about the ways early human lives are researched.
Where did modern humans originate from?
Despite the success and diversity of our ancestors, coupled with the fact that we still carry genetic information from our ancestors, only one hominin species survived: modern Homo sapiens. Not all scientists agree on the levels of contact or conflict that these early forms of humans had with each other, the extent of interbreeding that occurred, or the factors that influenced the evolution and extinction of other hominin species. However, from the recent discoveries described above, we know that early humans overlapped far more than originally thought. We do know that Homo sapiens evolved in Africa around 200,000 years ago and first migrated in small numbers into Asia, probably between 130,000 and 115,000 years ago, by travelling up the Nile to the Levant. However, the ancestors of all current humans migrated into Europe later, around 60,000 years ago, and it was not until much later still that modern humans populated other parts of the world. For instance, people probably first arrived in Australia within the past 50,000 years and in the Americas within the past 16,000 years or so. By 14,000 years ago, our species had spread to every continent except Antarctica. The beginnings of farming and complex societies occurred within the past 12,000 years. Understanding the success of our species remains a fundamental question for evolutionary anthropologists. This problem brings us back to the question of what differentiates us both from our closest living relatives, the apes, and from extinct hominins.
Similarities and differences between humans and nonhuman primates
So what characteristics do humans still share with other primates, and which are unique? Evolutionary anthropologists attempt to answer this question by comparing genes, morphology, physiology, behaviour and cognition in Homo sapiens and other primates. This section considers some of the main similarities and differences between them.
Humans and African apes share most of their DNA, but important functional differences have accumulated. Scientists have shown how humans continue to manifest striking similarities to the African apes both physically and genetically, especially to the chimpanzees and bonobos. For example, humans have forty-six chromosomes in their cells, while all the great apes have forty-eight. Research on mapping the entire genome of common chimpanzees was completed in 2005 and shows that 99 per cent of DNA sequences and 96 per cent of protein sequences of humans and chimpanzees are the same. This reflects the relatively recent split between the species since their last common ancestor 6 million years ago. However, it was discovered, unsurprisingly, that the genes that differ mostly control speech, smelling, hearing, digesting proteins and the likelihood of catching certain diseases, as well as the growth and efficiency of the brain, reflecting the fact that humans have been evolving separately for the past 6 million years.
ACTIVITY
Go to your local zoo or watch video clips of chimpanzees.
What physical similarities are there between humans and chimpanzees?
How do chimpanzees move?
Make a list of the behaviours that are similar to those of humans and those that are different, thinking, for example, about language, tools, parenting, learning, ways of thinking and social relationships.
All hominins and African apes lack external tails
Humans and the African apes all lack external tails. Monkeys, on the other hand, do have tails, which are useful for gripping trees and objects. Tails disappeared from apes 15–20 million years ago. Apes shin up and down trees rather than walking along branches as monkeys do. The earliest hominins climbed trees and walked on the ground. Fossil evidence shows how early humans made a gradual transition from climbing trees to walking upright on a regular basis.
All humans and African apes have opposable thumbs
Both humans and African apes have hands with a thumb that is sufficiently separate from the other fingers to allow them to be opposable for precision grip. Possession of an opposable thumb means that objects can be carried more easily and manipulated. There is considerable evidence to suggest that, by being able to throw and powerfully grip an object, early humans were better at protecting themselves from animals and other humans (Young 2003). The development of the opposable thumb, however, primarily helped humans to make tools, which was an essential advantage in human cultural evolution. But the mere presence of the opposable thumb does not explain why humans make sophisticated tools: if it did, then chimpanzees would make complex tools too (and they do not).
opposable thumb A thumb that is sufficiently separate from the other fingers of the hand to allow for precision grip
Figure 1.1 Hand of an African ape and of a human. (Denise Morgan for the University of Utah / Wikimedia Commons)
ACTIVITY
Take off your shoes and socks and sit on the floor. Try to open a banana skin with only your feet. What happens? What does this activity tell us about the advantages of having opposable thumbs?
Make a list of things that early humans might have been able to do as a result of having opposable thumbs. How might these activities have helped humans to survive?
Sexual dimorphism
Sexual dimorphism refers to both the internal and the external differences between males and females found in a variety of animals and plants. The earliest fossil evidence to show sexual dimorphism in early primates demonstrates that canine teeth and body shapes were different in males and females (Krishtalka et al. 1990). Hominins have not shown dimorphism in canine size, but there was a significant level of body size dimorphism in early hominins such as australopithecines. However, sexual dimorphism was significantly reduced in the larger-brained Homo erectus and their descendants (including Homo sapiens). This suggests an important development in social organization, with a possible change from polygamy (frequently associated with larger males) to monogamy (often characterized by low sexual dimorphism). Modern humans are sexually dimorphic to some degree. It is estimated that males are 5 to 10 per cent larger on average and have greater upper body muscular development. This is small compared to over 100 per cent body size dimorphism in gorillas and at least 15–20 per cent in chimpanzees and bonobos.
sexual dimorphism This refers to both the internal and the external differences between males and females found in a variety of animals and plants
STOP & THINK
Suggest some reasons
