The scientists found that there is a direct relationship between the size of the mammalian brain including humans and the amount of feeding time.
Longer time, bigger brain.
The discovery tends to add one more weight to the argument that "breast milk is the best" although researchers say they are not sure whether the energy is supplied by milk or whether the nutrients make up the difference.
"It supports the theory that breastfeeding and brain development are interconnected with each other," said researcher Professor Robert Burton at Durham University, as quoted by the Telegraph (29/03/11).
"What we do not know right now is whether there is something in breast milk that helps the brain to grow.
"The parts have been the subject of warm talk among scientists for some time.
"Currently we can not say for sure that formula milk is not an adequate substitute."
Prof. Barton and his team studied 128 species of mammals including humans, to see if there is a relationship between how much time is "invested" to nurture them and the size of their brains.
They found that longer periods of pregnancy and longer sucking directly affected brain size.
For example, in comparison, a deer that is approximately as heavy as a human, is only seven months pregnant and suckling for up to six months.
This causes a brain size that is six times smaller than the human brain.
"In general terms it does support the notion that 'best breastfeeding' and World Health Organization guidelines suggest that you should breastfeed for 18 months or two years is true," Prof. Drs. Barton.
Three years ago a study involving nearly 14,000 children found that those who sucked scored significantly better on IQ tests.
Another recent study published recently showed that babies were better at reading, writing and math activities at the age of five, seven, 11 and 14.
Breast milk has long been known to strengthen the baby's immune system that helps fight ear infections, abdominal pain and even asthma.
So if a mother really cares about her children's future, then she knows that her milk is already designed in such a way for the good of her children.
The new findings are published in Proceedings of the National Academy of Sciences.