Questions 22-32 are based on the following passage.
This passage is adapted from Robert Martin How We Dok. 2013 by Robert Martin
Rapid brain growth during the first year of life is connected with an unusual feature of newborn human infants: their striking plumpness. In an
Line average human newborn weighing some seven and a
5 half pounds, fat tissue accounts for over a pound,around 14 percent of body weight. Our babies are among the plumpest found among mammals. Human babies at birth look markedly different from the scrawny newborns of other primates, such as chimpanzees and rhesus monkeys. The proportion of fat tissue in a newborn human matches that in mammals living under arctic conditions and actually exceeds the level found in baby seals. As anthropologist Christopher Kuzawa has shown, a newborn human has about four times as much fat as expected for a standard newborn mammal of the same body size. In fact, the proportion of body fat in
a human baby increases further over the first nine months after birth, building up to about a quarter of body weight. During that period, around 70 percent of the energy allocated to growth is used to deposit fat. In short, healthy babies do not lose their baby fat after birth but consolidate it and maintain it for up to three years. A mother's investment in building up her infant's fat reserves continues long after birth,largely thanks to nursing.
A standard explanation for plump babies has been that natural selection favored an increase in body fat to offset the loss of insulating body hair.It is known that the optimal temperature for a human infant kept in an incubator is about 90 °F,
so cooling could be a problem. Baby fat is distinctively distributed, being mainly located just beneath the skin. In contrast to adult fat stores,
there is relatively little fat in the belly cavity. Anthropologist Boguslaw Pawlowski supported this view, arguing that various feature of human newborn evolved in early humans to counter excessive cooling during nights spent sleeping in open savannah. Those features include relatively large size as well as a greater proportion of subcutaneous fat.
However, Kuzawa's studies yielded only
weak evidence for the role of subcutaneous fat proposed by Pawlowski. Kuzawa went on to explore a more likely explanation for our exceptionally plwnp babies: increased fat reserves as a crucial energy buffer. This would be particularly advantageous during the period of rapid brain growth in the first year of life. It could offset any disruption in the flow of resources to the growing infant. Going a step further, a 2003 paper by two nutritionists, Stephen Cunnane and Michael Crawford, argued that plump babies are the key to the evolution of the large human brain, and not only because of energy supply. About half the brain consists of fat, and a baby's fat reserves contain special fats—long-chain polyunsaturated fatty acids (LCPUFAs)—that are essential for normal brain development. Calculations indicate that LCPUFAs present in baby fat at birth should be enough to fuel three months of brain growth. Deposition of fat in the hwnan fetus takes place only during the last third of pregnancy; almost no fat is present during the first six months. As a result, fat reserves are well below normal in premature babies. A baby born five weeks early has only half the usual amount of fat, and a baby born ten weeks early has less than a sixth. Insufficient fat deposits mean that preemies are not well buffered for the rapid brain growth that takes place after birth. Although normal brain growth can nevertheless occur given adequate nutrition, it is vital to recognized the special needs of premature babies. Cunnane aptly describes stored fat in the newborn hwnan as "insurance.