The Place of Nourishing Milk in Raising Offspring

"I was expecting something completely off the wall and different. But there are frightening, fascinating overlaps with mammalian milk in the kinds of proteins we see."
"Most female [tsetse] flies take a low-rent approach to parenthood, depositing scores of seed-sized eggs in the trash or on pet scat to hatch, leaving the larvae to fend for themselves. Not so the female tsetse fly. She gestates her young internally, one at a time, and gives birth to them live. When each extravagantly pampered offspring pulls free of her uterus after nine days, fly mother and child are pretty much the same size."
“It's the equivalent of giving birth to an 18-year-old.”
Geoffrey Attardo, professor of entomology, Department of Entomology, University of California, Davis

"The likely first function of milk was to hydrate parchment-shelled eggs laid on dry ground."
Amy Skibiel, mammalian lactation expert, University of Idaho

"Our ability to use animals in lots of different ways is one of the reasons we're successful, but it was a huge shock to the system."
"Our brain made our milk, not the other way around. The protein was through the roof, way above anything else in the milk."
"What does an armadillo build? A bony shell. So there's going to be a lot of calcium and phosphorus going into this baby."
"They'd [calcium and phosphorus minerals] get stuck in the mammary gland and never reach the baby. [The solution? Throw in extra doses of casein proteins to bind the minerals into compact, usable nano-clusters.]"
"If I'm going to have a high-calcium, high-phosphorus milk, I have to have a high-protein milk, because a lot of that protein is a calcium-phosphorus delivery device."
Michael Power, lactation researcher, Smithsonian National Zoological Park, Washington

As scientists learn more about milk’s evolution and compositional variations, they are redefining what used to be a signature characteristic of mammals. (The New York Times/Marcos Chin)

Entomologist Attardo discovered while analyzing tsetse fly milk that it was in fact a nutritional biochemical and immunological fluid designed and spun by the mother fly from blood meals, then pumped to her developing young. A fattened tsetse fly larva burrows underground to pupate for 30 days, then emerges as an adult. A chemical and genetic analysis of the fly's milk yielded the discovery of its similarity to milk extracted from mammary glands.

The research serves as an example of discovering the equivalent of mother's milk in a range of breast-free spieces such as spiders, cockroaches and burying beetles; and in great white sharks, male emperor penguins and flamingos (both male and female). Scientists have succeeded in tracing the evolution of mammalian lactation to conclude that the milk developed in aid of egg-laying creatures to solve the dilemma of dehydration on dry land. Other researchers set out to understand the compositional variances in milks from a broad sampling of the world's 5,500 mammals.

Lactation is expensive in terms of energy, demanding evolutionary justification. As an example, flamingos represent the few bird species that produce milk for their young, the effort draining their physical resources. A male and female flamingo build a nest together, incubate a single large egg and when the egg hatches begin to churn out milk to feed the chick for a nine-month period. The parents' brain is stimulated to production when from the hungry chick are heard and the hormone implicated is the very same one underlying human lactation.

Cells lining the crop at the base of the parental throat are prompted to swell and secrete the milk formula designed for the feeding of the young. It bursts with protein and the flamingo milk has more fat than that produced by mammals, as it "has the consistency of cottage cheese", according to Paul Rose, a researcher of flamingos at the University of Exeter in Britain. The milk is bright pink, spiked by the parents with the same carotenoid pigments that tinge a flamingo's feathers -- which happen to be antioxidants.

Zoltán Vörös/Flickr/CC by 2.0

As time passes in the nine-month period it takes to raise a chick, the parents must increase milk production to meet the growing demands of a growing chick, so that by the time the young flamingo approaches full-growth status, robust and pink-hued, the parents appear considerably thinner and utterly depleted, their feathers once fuchsia, turned wan white with the effort of feeding their chick. Pre-mammals were thought to dribble fluid onto their eggs through pores on their chest, the fore-running biological design of nipples which would much later evolve.

Genetic studies point to egg hydration solutions fortified with anti-pathogen components in response to the vulnerability of parchment eggs at risk of microbial infiltration. Natural selection stepped in to make use of the watering post-hatch to integrate food for babies with the anti-pathogen components. Milks diversified, their content dictated by need, diet and genetic diversity. An example of that can be seen in the amount and variety of sugars in human milk, far outstripping the content in any other great ape, according to Michael Power.

This lactation researcher propounds a theory that humans require sugar's antimicrobial power to aid in coping with all the pathogens encountered while historically living in close proximity with other animals; not the theory extended by other researchers that the nutritional compounds were designed to build our larger brains.