List of Headings
- i A puzzling development in early humans
- ii A number of disadvantages relating to human posture
- iii Evidence of problem-solving skills in other mammals
- iv Statistics concerning the relative volume of human brains
- v The role of competition in human evolution
- vi The positive and negative effects for humans of infant dependency
- vii A common assumption which lacks validity
- viii Manual dexterity as a defining characteristic
- ix The costs involved in maintaining a very heavy brain
Questions 1-7
Drag a heading to each paragraph.
1. The earliest men and women 2.5 million years ago had brains of about 600 cubic centimetres. Modern men and women sport a brain averaging 1,200–1,400 cubic centimetres.
2. That evolution should select for larger brains may seem obvious to us. We are so proud of our high intelligence that we take for granted that when it comes to cerebral power, more must be better. But if evolution worked in this way, the feline family would also now have produced cats that could do advanced mathematics, and frogs would, by now, have launched their own space programme. Why are giant brains so rare in the animal kingdom?
3. In modern humans, the brain accounts for about 2–3 percent of total body weight, but it consumes 25 percent of the body's energy when the body is at rest. By comparison, the brains of other apes require only 8 percent of rest-time energy.
4. But cars and guns are a recent phenomenon. For more than 2 million years, human neural networks kept growing and growing, but apart from some flint knives and pointed sticks, humans had very little to show for it. What then drove forward the evolution of the massive human brain during those 2 million years? Frankly, we don't know.
5. The first evidence of tools being produced dates from about 2.5 million years ago, and their manufacture and use are the criteria by which archaeologists identify ancient humans.
6. Yet walking upright has its downside. Humankind paid for its lofty vision and industrious hands with backaches and stiff necks. Women paid extra—an upright gait required narrower hips, constricting the birth canal—and this just when babies' heads were getting bigger and bigger. Death in childbirth became a major hazard for ancient human females.
7. Raising children required constant help from other family members and neighbours. It takes a tribe to raise a human. Evolution thus favoured those capable of forming social ties.