Slime molds were appealing to me and everybody else because of the fact that the cells come together and form a multicellular organism. So normally that's not the way it works. Normally, you have an egg, a fertilized egg, usually and that divides and divides and becomes bigger and bigger, and slowly turns into a toad or a flower or whatever.  Now these organisms do all their eating first so that they seem to be going in reverse, as it were. Because they feed just the way our white blood cells feed, on bacteria that have invaded our body, they feed on bacteria as individual amoebae. In fact, they're about the same size and their appearance is very similar to our white blood cells, only they live in the soil. They are no parasitic ones. But in any event, they really have a totally different way of becoming multicellular. And so as soon as I started working on them, this is the first thing that came to mind was why do they come together? Why do they aggregate to form these maybe one or two million cells with an organism that has a front end and a hind end and produces spores at the top and stalk cells below? What makes it do all that, what are the immediate causes? And I found that in the first place, I settled a question which had been an open question for quite some time. Some of the early work goes back to 1900. And that is the question of what attracts them to the central collection point? They do this when they're satiated, when they're full of food and no more food is available, and they start to starve, then they do this. So that seemed very mysterious. And there were lots of ideas about how they did this, but none were really satisfactory. And so that was my PhD thesis.