View Full Version : Taste for meat made humans early weaners

Friday, January 28th, 2005, 10:41 AM
Taste for meat made humans early weaners

19:00 26 January 2005
Exclusive from New Scientist Print Edition
Anna Gosline

A taste for meat prompted early humans to wean their children at a young age. The idea explains why we now wean our infants years earlier than other great apes.

In non-industrialised societies, women breastfeed their children for an average of two and a half years, while chimpanzees feed theirs for five. Anthropologist Gail Kennedy of the University of California, Los Angeles, US, suggests that humans made the transition to early weaning 2.6 million years ago.

That was when a branch of hominids began to eat animal carcasses - a risky activity that would have brought them into contact with other predators and significantly raised mortality rates for the hunters. This would have created a selection pressure to wean infants earlier and earlier, since those no longer dependent on breast milk would have been more likely to survive their mother's death, says Kennedy.

What is more, the nutritional benefit of eating meat at a younger age would have helped children's brains to grow and develop more quickly. Human brains grow three times quicker than those of chimpanzees.

But Barry Bogin of the University of Michigan at Dearborn, US, has a different rationale for early weaning. He believes it allowed hominid mothers to have more offspring. "By weaning at 30 months, we have a great reproductive jump over our closest cousins; we can crank out two babies in the time it takes a chimpanzee to have one," he says.

Journal reference: Journal of Human Evolution (DOI: 10.1016/j.jhevol.2004.09.005)


Friday, January 28th, 2005, 09:53 PM

We've all heard of the "big bang" theory of the origin and evolution of the universe. Now we have what might be called the "big brain" theory to explain the origin and evolution of homo sapiens . Of the large mammals, only the dolphin comes anywhere near the same brain-to-body size as humans. How did we evolve this way? What gave us this apparent advantage over other species?

In The Driving Force: Food, Evolution, and the Future, Michael Crawford, PhD, head of the Department of Nutritional Biochemistry, Nuffield Institute of Comparative Medicine, Institute of Zoology, London, England, and David Marsh have given us a plausible answer. Dr. Crawford is an international authority on the nutrition and diseases of peoples around the world. For many years he did intensive research in Uganda, Africa, where extreme differences in climate, vegetation, and wild life present a microcosm of peoples and animals with correspondingly extreme differences in nutrition and diseases.

"The fact that evolution concerned different ways of getting food is such an obvious statement and the business of eating is of such a commonplace nature, that its central importance has been overlooked."

"East Africa, and particularly Uganda, is a fertile area for research into nutrition. Uganda is a country of great contrasts: here are the snow-capped Mountains of the Moon, the crater lakes of the Queen Elizabeth Nation Park, the Semiliki Plains, moving with the gold of the Uganda kob, and the waters of Lake Albert with its giant Nile perch. Then there are the impenetrable forests of Kabale with dense undergrowth and high canopies out of which the steam clouds rise to moisten the morning air. These contrast with the semi-arid plains of Karamoja, where giraffe and eland thrive on the deep-rooted acacia and balanites trees even in the burnt landscape of the dry season. Around Lake Victoria the vivid greenness, the equatorial rain, sunshine, and soil combine to create what is perhaps the greatest biological productivity in the world."

Based on their research, Crawford and Marsh consider food the driving force in the evolution of living organisms on Earth: "The fact that evolution concerned different ways of getting food is such an obvious statement and the business of eating is of such a commonplace nature, that its central importance has been overlooked." While they agree with Darwin that "survival of the fittest" is important when resources of appropriate food become scarce, they stress Darwin's observation that "conditions" are crucial. In other words, particular organisms must have the appropriate chemicals, i.e., nutrients, in order to develop.

About 500 to 600 million years ago, say the authors, living organisms made a quantum leap into more-complex, multicellular designs--a change fueled by not only oxygen, but also structural lipids (fats needed for membranes in body cells, particularly for the development of the nervous and circulatory systems)--and big-brain evolution was under way.

Since those early years, the basic chemistry of life has remained unchanged.

"The way in which modern plants absorb sunlight, use its energy to promote chemical reactions, and excrete oxygen into their surroundings is the same (as far as we know) as that of the earliest forms of life. Still more curiously . . . the chemistry that transports oxygen in our human bloodstream is the same in all mammalian species. Indeed, the key processing systems in our bodies have not radically changed from those of the first microscopic creatures that drifted in the primeval oceans. . . . Such persistence over millions and even billions of years [would be explained by life changing] according to a programme dictated by the nature of chemistry and the environment. The presence or absence of chemicals like oxygen, or nutrients like vitamin A, make certain directions possible or impossible. When chemical support systems for a particular line of species are exhausted, the biochemical system cannot cope, the line collapses and creates a new discontinuity."

Crawford and Marsh theorize that our ancestors developed on the shores of oceans and rivers, areas with a great abundance and diversity of food. They suggest that our relatively large brain, which "uses as much as 20 percent of the body's energy although it occupies only 2 percent of the body," could develop in such a seashore area because all the necessary nutrients were available in abundance. Our vascular system that carries oxygen and nutrients to our cells and removes their waste products "evolved together with the brain, [which is] critically dependent on its blood supply; clamp off its supply for five minutes, and the brain dies."

While we have three to six times more omega-6 than omega-3 fatty acids in organs other than our brains, the brain requires a one-to-one balance of these substances. And [i]no animal, including ourselves, can convert an omega-3 fatty acid to an omega-6 or vice versa. For these ratios, then, we are dependent on what we get in our food.

Surprisingly, 60 percent of the building materials of the brain and nervous system is fat. say the authors--not just any kind of fat, but lipid or 'structural' fat. Both our nervous and circulatory systems depend on fats--certain kinds for certain purposes. For example, some saturated fat is needed to give rigidity in the protective sheath around nerves and to "make sure messages do not short-circuit and go to the wrong place." On the other hand, for nerve transmission the brain requires the long-chain, most unsaturated fatty acids, , the "neural" fatty acids, those that are most chemically reactive and most easily destroyed by oxygen. Fortunately, vitamins C and E, which react even more easily with oxygen, can help protect the unsaturated fatty acids.

Vitally important for our food intake are two families of unsaturated fatty acids: omega-3 and omega-6. Both are essential and both must be acquired from food. While we have three to six times more omega-6 than omega-3 fatty acids in organs other than our brains, the brain requires a one-to-one balance of these substances. And no animal, including ourselves, can convert an omega-3 fatty acid to an omega-6 or vice versa. For these ratios, then, we are dependent on what we get in our food.

The brain and vascular system use the most unsaturated fatty acids. "The brain sends and receives many millions of messages every second and is the most membrane-rich system in animals. Blood vessels are also highly dependent on membrane fluidity. The blood vessels of modern animals use polyunsaturated fats to provide the flexibility that allows them to absorb the pressure waves generated by the pumping heart. Without that flexibility we get hardening of the arteries and a fatally inefficient vascular system." The most polyunsaturated fatty acid (docosahexanoic acid, from the omega-3 family) makes up 60 per cent of the structure of the photo receptors in the eye. One part of this structure can send "10,000 signals approximately every 1/25 of a second to the corresponding network of brain cells." (IBM and Apple, take notice!)

Seafood is an excellent source of unsaturated fatty acids, particularly the omega-3s. Crawford and Marsh theorize that our brains developed along with our increased body size because we had the abundant nutrients, including minerals, vitamins, and both families of fatty acids, that are available on the seashores. They point out that all savannah animals that increased in size lost out in relative brain size. They speculate that our ancient relative, Australopithecus, with a large pelvis and small brain, "having become land-locked, became a degenerate side-shoot which, like the savannah species, followed the common path of increasing body size outpacing the growth of the brain." Thus it may be that we humans owe our pre-eminent brainpower to the sea, with its abundance of omega-3 fatty acids. The old notion that fish are brain food may not be far-fetched after all.

Most of the brain's development takes place in the womb. "Inside the womb the foetus 'eats' the food that the mother supplies; this food has previously been processed by the mother's own digestive system, including her liver. Just as a carnivore eats the end-products of another animal's efforts, so a foetus is nourished entirely by the end-products of its mother's work." Actually, it has been found that the human placenta selects "the long-chain neural fatty acids used in the brain from the mother's blood, and passes them on at higher concentration to the foetus. We can see a foetus--even of a vegetarian animal--as a kind of super-carnivore.

The process of biomagnification applies to other nutrients as well, but in the case of the EFAs [essential fatty acids] it specifically selects the neural," thus taking care of the growing brain's important needs. In a study of babies born without any brains (anencephalic) compared with those with normal brains, it was found that "a staggering 60 to 70 per cent of the newborn's energy from food and reserves is used by the brain for growth and maintenance. Indeed, the brain is so rich in lipid that its metabolic rate per unit of cell mass is phenomenal."

Crawford and Marsh theorize that our brains developed along with our increased body size because we had the abundant nutrients, including minerals, vitamins, and both families of fatty acids, that are available on the seashores.

In one experiment, when a rat mother nursed 14 pups rather than 4, the pups in the large group had relatively tiny brains, and no later improvement in nutrition could make up the difference. Another experiment "similarly showed that if lactating rats were fed on a diet deficient in EFAs their pups sucked deficient milk and suffered permanent learning defects, which could not be reversed by giving them a correct diet after weaning."

The essential fatty acids are far from the only essential nutrients, however. Crawford and Marsh describe the widespread blindness in India due to lack of vitamin A in the diet. "The exclusion of green foods, liver and other sources rich in beta-carotene and vitamin A resulted in blindness. Today much of the world's nutritional blindness is in India."

They also point out how animal husbandry and agriculture have changed our food, resulting in particular diseases from particular deficiencies and excesses. All year round, for maximum weight-gain, we feed our cattle and other animals the energy-rich food they would only find naturally in the springtime. Then, we restrict their exercise so that they are essentially obese with even their muscles infiltrated with saturated (storage) fat. Themselves unhealthy, they provide us with unhealthy food.

Nutrition, say Crawford and Marsh, is not just

"a set of individual drug-like vitamins: it is multifactorial. Food is several things but different foods provide different groups or clusters of nutrients. It is not just the single nutrient that matters: the relationship between them matters too. Different animal species have different requirements and in the mammals this truth is reflected in the composition of their milks, which are rich in protein on the one hand for fast body growth or rich in essential fatty acids on the other, when the postnatal focus is on brain growth."

Concerned about the future of our species, the authors warn: "We would not want to deliberately decrease brain capacity but this could happen if we are not careful." Scientific experiments have demonstrated many of the nutrients needed for excellent brain and body development. However, our food industry has worked to supply food cheaply to the huge numbers of people that now live in urban areas. Pursuing this goal, they have eliminated the easily destroyed "neural" fatty acids both by hydrogenation (forming margarines) and also by choosing naturally-less-unsaturated as well as saturated sources of fat.

Crawford and Marsh conclude:

"In the human species the highest specialization, which stands out head and shoulders above other species, is the brain and it is built in the womb of the mother. . . . The challenge we face is clear: it is to stop the degenerative diseases and, instead, to continue the evolution and development of the human brain and intelligence. . . . To respond to this challenge requires knowledge, particularly on the part of women, whose bodies and minds hold the responsibility for the next generation . Yet in our present day world, two-thirds of women are illiterate and only 1 percent own property. One highly placed World Health Organization worker commented that if he had a choice, he would give education to the girls in preference to the boys. . . . Standing at the moment of intersection between the vast gulf of the past and the dangers and promises of the future there stands a figure whose importance overwhelms all others: the figure of a human mother and child."


"Women in developing countries are shortchanged by some pervasive cultural norms. They not only work harder, studies have shown, but they often get proportionately less to eat than men in Third World Nations."--Dartmouth Medicine , Spring 1991, p. 25.


Here, from NOHA NEWS of Fall l987(slightly modified), are some important fatty acids and some of their food sources:

Omega-3 fatty acids

alpha-linolenic acid (18:3)

high in linseed (flaxseed) oil
moderate in soybean and walnut oils

eicosapentaenoic acid (20:5)

high in the fat of cold ocean fish

docosahexaenoic acid (22:6)

high in the fat of cold ocean fish

Omega-6 fatty acids

linoleic acid (18;2)

high in corn, safflower, and sunflower oils
moderate in soybean and walnut oils

gamma linolenic acid (18:3)

high in evening primrose oil

arachidonic acid (20:4)

high in peanut oil and meat

The first number in the parentheses is the number of carbon atoms in the fatty-acid chain; the second number is the number of unsaturated centers in the chain. Thus docosahexanoic acid is the longest and most unsaturated of these examples of fatty acids.

Modern pollution reaches even the distant, cold oceans.

At this point some of you will be saying to yourselves, "But pesticides and other contaminants end up in fatty tissues. Why should we be eating the fat of cold ocean fish to get our omega-3s?" You have a point: modern pollution reaches even the distant, cold oceans.

For this dilemma there is no good answer--only a trade-off until society, as a whole or as its more responsible members, decides to modify its overuse of toxic chemicals. In the words of Crawford and Marsh:

"We need above all to understand that the care of our environment is not an optional extra, a harmless pastime for the well-fed middle classes, but the central task for our age. If we fail in that we fail in everything, for we are a part of that environment."

Article from NOHA NEWS, Vol. XVI, No. 4, Fall 1991, pages 1-3,6.


Dr. Solar Wolff
Saturday, January 29th, 2005, 02:57 AM
Neandertals had big brains yet no fish or shellfish are found in their habitation sites. Their diet was about 87% animal products so this was surely meat and marrow. I wonder about the Omega 3 and 6 content of marrow. If it is high, it would explain alot.