To abstract the abstract:

2 to 3 million years ago, a gene in early humans was permanently inactivated (perhaps due to a malaria-like outbreak targeting a cell-surface molecule that the protein the gene coded for helped to build). That cell-surface molecule is found in most other mammals (excepting humans, ferrets, platypuses, and New World monkeys) so consumption of certain meats can cause it to be taken up and incorporated into human cell membranes, as the genes that allow for this are still functioning. But the immune system becomes sensitized to it, as a foreign antigen, and produces antibodies that subsequently cause chronic inflammation in the cells that took it up and exposed it on their surfaces.