Synthetic flesh. (Courtesy of King's College London's Materials Library.)
Synthetic flesh. (Courtesy of King's College London's Materials Library.)

Most people are reasonably comfortable with the idea of reducing their air travel, if it is going to save the planet. People are even buoyant about the idea of driving a different kind of car, especially if it is going to be as cool as the DeLorean fueled by rubbish in the film Back To The Future. So it came as a big shock recently when a much more unpleasant fix to global warming was mooted, namely that we all give up eating meat.

Calculations show that not only is the production and distribution of animal flesh for consumption incredibly carbon intensive, but the knock-on effect of having billions of domestic animals farting methane (a potent greenhouse gas) seriously compounds the problem. All of a sudden, eating a steak has become not just an ethical statement, but a moral act: an act with consequences including the melting of ice caps and the demise of civilization as we know it.

Will climate change spell the end of the human love affair with animal flesh? It'll be tough weaning ourselves off it because flesh has played a major role in our development as a species: it is at least as important as stone and metals.

First, there was the production of fur, leather clothes, bags, and sturdy shoes, which even now are hard to beat, even when using oil-derived polymer composites. Animal skin is a remarkable material, tough, elastic, plastic, waterproof, and as anyone who as ever written on their hand will know, it is capable of absorbing dyes and pigments. This not only makes tattoos possible, but more importantly for the history of ideas, it can be made into an incredibly durable writing material called parchment. Here knowledge can be recorded, efficiently stored, and handed down through the generations.

This ancient technology involves the flaying and dehairing of skin into thin sheets made almost entirely of bound collagen. Go into any of the great libraries of the world and you will find most of the ancient books are made of animal flesh. Indeed, parchment is still used: the British do not trust any other material on which to record their Acts of Parliament.

These days parchment has been mostly replaced by paper, leather has been challenged by plastic and rubber technologies, but synthetic replacements for a juicy steak are as yet poor mimics, even if they can make up for the protein we get from meat. The best of these is perhaps the Chinese and Japanese tofu. In general, the hard thing to replicate is not the flavor. Rather it is an olfactory and textural combination, something for which the English language has no word but which translates from the Chinese as ‘mouth-feel’. Despite the demand, no tofu comes really close to the experience of eating animal flesh. It is the macromolecular assemblies at different length scales that gives meat such a complex flavor and texture, a structure-property relationship that we are able to sense, taste, and crave. Indeed, the production of animal flesh to satisfy this craving is extremely big business. In the US, until recently it was second only to the car industry in size.

Oddly enough, the production of synthetic human flesh has made much more progress. This started off as basic silicone and saline implants for breast and buttock enlargement. But tissue engineers are now working to use stem cells to grow three-dimensional, functionally layered, multiscale tissue structures with a working blood supply (the really tough bit). There are many problems to be surmounted before the growing of replacement flesh outside the body becomes a standard clinical approach to organ failure, disease, injury, or vanity. But if we crack it, an obvious question will be whether the technology should be limited to medicine, or could it also be used to produce in vitro flesh for consumption.

Artists are already using bioengineering as a form of self expression. Perhaps it won't be long before experimental chefs like Heston Blumenthal start to take up tissue engineering. This may seem an obvious solution to the ethical and environmental dilemmas raised by killing animals for meat. But then what of the rights of such test-tube steaks? As Portia warns Shylock in Shakespeare's The Merchant of Venice, where there is blood involved, such issues are never as simple as they seem:

Tarry a little, there is something else.

This bond doth give thee here no jot of blood;

The words expressly are “a pound of flesh.”

No doubt we will find some similar small print as we try to flesh out the ethics of tissue engineering in the 21stcentury. What ever happens there may never again be such a thing as a guilt-free steak.

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DOI: 10.1016/S1369-7021(08)70037-3