For several reasons, some to do with health, others with moral convictions, Western society has moved away during the past decade from eating meat towards a vegetarian diet.
Historians, who are privileged to view societies from the high ground of the future, one day will probably view our consumption of meat from animals as one of the last vestiges of barbarism, just as an enlightened 21st-century society now views the evil centuries of the slave trade with abhorrence.
Most Westerners remain unaware that the majority of humans on the planet eat meat sparingly or not at all.
Several billion people exist on a staple diet based on cereals like rice, wheat, maize or millet, pulses such as beans and peas, or root crops such as cassava or potatoes; meat is either unavailable, forbidden by religion, or an unaffordable luxury.
But there is also a sound scientific reason for eating plant foods instead of meat, which has to do with the energetics of the food chain that links plants, animals, and humans.
Plants are the ultimate source of food for almost all terrestrial organisms, using photosynthesis to transmute solar energy into chemical energy – carbohydrates, proteins, and lipids (fats).
A cow or sheep grazing on grass, or waxing fat on grain in some feedlot, transforms only about 10 percent of the food energy in plants into meat, bone, and other tissues.
While the remaining 90-odd percent is not wasted – much of it goes into stoking the biochemical fires that keep the animal alive, warm and functioning – it is unavailable to the next link in the food chain.
When humans eat meat or any other food, the energy losses are of a similar order, so that the amount of energy that passes from the original plant to us by way of animal tissues is just 1 percent. Put another way, it takes 100 kilograms of plant material to make 10 kilograms of cow, and 10 kilograms of a cow to make one kilogram of human.
As omnivores, humans can substitute for herbivores as the second link in the food chain.
If we eat plant foods, it takes only 10 kilograms of plant food to make a kilogram of human, so that 10 human vegetarians can be fed off the same area of land that formerly fed only one human meat-eater.
These calculations are only approximations, but even allowing a considerable margin for error, they make a strong case for humans reverting to the essentially vegetarian diet of their primate ancestors. But there are some complications.
Humans require a diet with an appropriate balance between about 20 amino acids, the building blocks for proteins.
Most amino acids are synthesized naturally in the body, but some, like vitamin C, can only be obtained, through the diet.
People who eat a balanced diet of meat, dairy products, cereals, fruit, and vegetables, should not suffer amino acid deficiencies or imbalances.
But vegetarians have to be more careful because the main proteins in certain cereals and legume seeds have a less than ideal amino-acid imbalance.
But in the foreseeable future, humans may be able to forgo their steak and eat it too.
From eating textured vegetable proteins masquerading as meat, we may move to eating plant-derived foods containing proteins borrowed from the animal kingdom, without any exploitation of the animals themselves.
CSIRO scientists have experimentally spliced a chicken gene, coding for the egg white protein ovalbumin, into lucerne plants. Ovalbumin is rich in sulfur-containing amino acids, and the objective is to stimulate wool growth in sheep grazing on transgenic lucerne.
The same research team has isolated most of the genes for the various proteins in legume seeds, and plant genetic engineers may have developed their technology to the point where, by splicing the appropriate genes into crop plants, they will be able to mix-and-match these proteins with the genes of selected proteins from other plants or animals to improve the nutritional qualities of legumes like peas and soybeans.
The seed proteins in legumes like peas and soybeans tend to be deficient in the sulfur-rich amino acids cysteine and methionine, while other legumes like lupins have anti-nutritional factors such as alkaloids that make them unsuitable for human or animal consumption.
Using conventional breeding techniques, breeders in Western Australia have already bred low-alkaloid lupin varieties suitable for animal consumption, in the process turning a pretty garden plant into a profitable new export crop.
Genetic engineering should augment and speed up conventional plant breeding. Apart from introducing new genes into plants, it will make possible precise genetic surgery to remove or silence unwanted genes in existing varieties.
Broad beans, for example, contain an amino acid that causes a disease called favism in many people from the Mediterranean region who carry a gene that protects them from malaria.
Chickling pea, a legume that forms the staple diet of people in some regions of India, contains a toxic amino acid that can cause brain damage and paralysis in susceptible individuals. Selective DNA surgery could remove the unwanted protein.
Legumes are an obvious target for genetic surgery to improve their nutritional properties – the world would jump at baked beans that had been edited to excise the well-known “Blazing Saddles” factor, while the soybean market might welcome products that contained no hint of the “beany” flavor that some people find unpleasant.
But most of the world’s vegetarians have a staple diet of cereals, rather than legumes. Cereals present special problems, both to the conventional plant breeder and the genetic engineer.
Wheat, corn, rice, barley, oats, and millet are all members of the grass family (monocots). Monocots offer a double challenge to genetic engineers – they are difficult to regenerate from single cells in tissue culture and are not susceptible to infection by the plant genetic engineer’s little helper, a special strain of bacterium called Agrobacterium tumefaciens, which is used to insert new genes into plant cells.
Japanese researchers several years ago solved the problem of regenerating rice cells in tissue culture, but nobody has been able to put new genes into tissue-cultured rice cells, regenerate fertile plants, and grow from their seeds the second generation of plants in which the new gene is stably integrated.
Very recently, a team from the plant sciences section of the Swiss Federal Institute for Technology in Zurich achieved this second milestone. Dr. Swapan Datta, Dr. Alex Peterhans, Dr. Karabi Datta, Dr. Ingo Potrykus have established a laboratory protocol for producing transgenic rice plants that will now be taken up by rice breeders around the world.
About two billion people eat rice as their main source of food every day, in countries where animal protein is typically scarce or costly.
Swapan Datta’s team has brought within sight a day when the animal or other important proteins might be introduced into rice by genetic engineering.
There are rumors that plant genetic engineers have done the same with corn. Zein, the main protein in corn kernels, is deficient in tryptophan and lysine.
No such progress can be reported for wheat, Australia’s most important crop, which is deficient in lysine.
But there is more than one way to skin a wheat cell, and more than one way to introduce new genes. Watch this space.