Question: What is a “food web?”
Joel Cohen: A food web is a description of which species living in a place eat which other species. You can think of it like a roadmap with one-way streets. It shows you, if there's an arrow from A to B, it means the energy flows from A to B, or in other words, B eats A, okay? So it's usually drawn with a bunch of circles, you put the name of a species in the circle and then you draw an arrow showing which way the food is flowing. Okay? That's what a food web is.
Now, we have just been talking about a food web. We've been talking about the food web in which people eat ducks, geese, swine, cattle, okay? And, what most people don't realize is, the things that eat us are the infectious diseases, like the viruses and the bacteria and the worms and the other parasites, much more important than the lions and the tigers.
And what I've been studying is how the animals we eat put us at risk of being eaten by the infectious agents that eat those animals. So when we eat the duck, it puts us at risk of being eaten by the virus that eats the duck, the H5N1. But let me give you some other examples, okay? The monkeys that live in the forests of west Africa, have long been infected by a virus called the simian influenza—sorry, simian immunodeficiency virus. Okay? SIV. We now believe that people went hunting for those monkeys and either got the blood in their hands or ate them without cooking them fully, and the simian immunodeficiency virus infected the people who were dealing with the blood from those animals and evolved very slightly, because we can compare the genes, and gave us the human immunodeficiency virus, HIV. So by going into a new habitat, eating the monkeys and getting their blood, the things that were eating the monkeys turned to eating us. That's the current understanding of the origin of HIV. It was going after food in the forest.
Another, okay, do you follow that? We've talked about avian influenza, that's from the expansion into new habitats. Another example is swine flu and trichinosis. We eat the pigs, the worms of trichinosis, if they're not cooked to death and we eat uncooked ham or pork, they start infecting the people. The influenza that swine have infects the people who live with the swine. A last example, mad cow disease. Mad cow disease is a prion that causes bovine spongiform encephalitis, BES. If you eat the flesh of a cow that has been eaten by one of those prions, it will eat you, and then you get Jackob Creutzfeldt disease.
And, so there's a World Health Organization for animals, did you know that? Probably not. It's World Organization for Animal Health, it's called, and they have a long list of what are called zoonotic diseases. And a zoonotic disease is a disease that regularly infects vertebrates and will also infect people if they are exposed to it. And many, many, many of those zoonotic diseases are diseases that arise because we raise domestic animals for meat. So there's a connection with the meat and our health that's very close.