The study of 128 mammal species, including humans, shows that brain growth in babies is determined by the duration of pregnancy and how long they suckle. The Durham University and Queen’s University Belfast research concludes that the longer the pregnancy and breastfeeding period in mammals, the bigger the baby’s brain grows.
The researchers say the findings reinforce the suggestion that breast is best for brain development and add further weight to the World Health Organisation’s advice of six months’ exclusive breastfeeding followed by continuing breastfeeding up to the age of two or beyond supplemented with solid foods.
The study, published in the Proceedings of the National Academy of Sciences, helps to explain why humans, who suckle their babies for up to three years in addition to their nine-month pregnancies, have such a long period of dependency as this is necessary to support the growth of our enormous 1300cc brains.
In comparison, species such as fallow deer, which are about the same body weight as humans, are only pregnant for seven months with a suckling period of up to six months, resulting in brains of only 220cc, six times smaller than the human brain.
The anthropologists, from Queen’s University Belfast and Durham’s Evolutionary Anthropology Research Group analysed statistical evidence on brain and body size, maternal investment, and life history variables in mammals, including species such as gorillas, elephants and whales.
They found that brain size relative to body size was most closely linked to maternal investment – the amount of time a mother spends carrying her offspring in pregnancy and how long she continues to breastfeed. The study shows that length of the pregnancy determines brain size at birth and the period of lactation decides brain growth after birth. It also shows that mothers with higher metabolic rates can afford to fuel faster brain growth in the foetus.
Co-author of the investigation, Dr Isabella Capellini from Queen’s University said: “Our study shows that the slower pace of life and increased lifespan in species with larger brains are a consequence of the greater costs of growing large brains more than the benefits for reduced mortality. These costs are certainly offset by some benefits, and our research suggests that these are more likely related to improvements in specific perceptual and cognitive abilities rather than a more general flexibility on behaviour and cognition as so far suggested.”
“Our findings help us to understand what the implications are of evolutionary changes at different stages, before and after birth, but we now need to do more research to pinpoint exactly how changes to the pre- and postnatal growth phases affect the structure of the brain.”
The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Natural Environment Research Council (NERC).
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