Q11.
In many animals, the young ones can walk or find food soon after birth but human babies are completely dependent on adults for a long time. What might be some advantages and disadvantages of this for humans as a species?
Answer
The long dependence is the price humans pay for a large, slowly-built brain — and the learning that this makes possible is precisely what has made the species successful.
| Advantages | Disadvantages |
|---|---|
| The brain can keep growing and wiring itself after birth, so it need not be finished before the head passes the birth canal | The child is helpless for years and needs constant care and protection |
| A long childhood is a long period of learning — language, tool use, skills, customs and values are passed on by teaching, not only by inheritance | Enormous cost in food, time and energy to the parents and the family |
| Breastfeeding gives complete nutrition and protection against many diseases, as the chapter notes | Few offspring in a lifetime; the mother's next child is delayed for years |
| The need for care builds strong family and social bonds, and brings grandparents and the community into raising the child | If the parents fall ill or the family lacks support, the child's survival is directly at risk |
| Behaviour can be adapted to a new place or a new problem within one generation, without waiting for inherited change | Population grows slowly, so recovery from a disaster takes a long time |
Why the trade-off is the same one seen throughout this chapter: Table 11.4 shows animals choosing between many offspring with little investment and few offspring with heavy investment. A frog lays 5,000 – 50,000 eggs and leaves them; a bird lays 1 – 15 and feeds them. Humans sit at the far end of that same line — usually one child at a time, cared for over many years, with survival correspondingly high. The helplessness of a human baby is not a flaw in the design; it is what a very heavy investment strategy looks like.
Tip: a horse foal walks within an hour of birth because a foal that cannot run is eaten. A human infant does not walk for a year because it is protected by adults during that year. Each pattern fits the way that species lives, and neither would work for the other.