I read that an artery is a blood vessel that carries blood away from the heart. However, a dead body still has arteries, and they don't carry blood anywhere anymore. Moreover, there may be dead or non functioning arteries within a living body. A friend of mine suggests that an artery is a blood vessel that evolved to carry blood away from the heart, but a creationist wouldn't believe her, and I would prefer a definition of "artery" that could be accepted by anyone. Could you, philosophers, provide such a definition?

Your question relates directly to a central issue in the philosophy of biology, which is how to understand what it means to say that a biological trait has a particular function. The appeal to evolution by natural selection is attractive here because we often seem to explain why a trait is present by appeal to its function, and this practice would otherwise be strange, since functions are effects and we don’t normally take effects to explain their causes. Thus suppose we say ‘We have arteries because they carry blood away from the heart’. Carrying blood away from the heart is an effect of having arteries, so how can it explain why we have them? But in the context of natural selection, we can say that it is because arteries in our ancestors carried blood in the past that we are here now, arteries and all. So the functional explanation ‘We have arteries because they carry blood away from the heart’ is actually not an ‘effectal’ explanation, but a causal explanation. What explains and causes arteries today is blood getting carried in the past and the selection of creatures who could do that sort of thing.

Nevertheless, I take your point that when we simply characterise something in functional terms we do not seem to be committing ourselves to an evolutionary theory. People talked about functions and defined things in functional terms before Darwin. So maybe we can define arteries in terms of their function – carrying away blood – and understand function not in terms of natural selection but rather in terms of the characteristic contribution that arteries make the operation of the organism as a whole. It’s true a dead person still has arteries even though they are no longer carrying blood, but that’s because those tubes are similar to the ones that are doing their job in normal living individuals.

If you want to follow up the philosophy of biological function, a good anthology is Nature’s Purposes, edited by Colin Allen, Marc Bekoff, and George Lauder.

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