I performed a broad survey of the genomes of animals and their single-celled close relatives, searching for genes encoding proteins or protein domains that in animals play a part in regulated cell death. I found that the major elements of the best-known regulated cell death pathways, apoptosis, emerged at the onset of animals; but that some accessory proteins that are now involved in regulated cell death were already present before the origin of animals, in their single-celled ancestors. These include downstream effectors of apoptosis, inhibitors of apoptosis, and elements of caspase-independent regulated cell death pathways. It is possible that these genes had a different function in the single-celled ancestors of animals, and that they underwent a change of function ('functional cooption') as animals arose. Alternatively, it's possible that single-celled ancestors of animals already had simple forms of regulated cell death, perhaps protecting against the spread of infection through a population. Using cutting-edge genetic tools developed in the Multicellgenome lab, I am studying how some key genes behave when they are manipulated in single-celled relatives of animals, to understand what their original functions may have been in the single-celled ancestors of animals, and what changes they may have undergone as animals evolved.