Hello everybody, welcome to the Mindscape Podcast. I'm your host Sean Carroll.

Life is complicated. I don't mean your life, my life. Those are also complicated, but as we all know,

biology is complicated. The history of biology is complicated. Here on Mindscape,

you know, I'm interested in very big questions like the origin of life. But we also have the evolution

of life, right? That's interesting all by itself. And so there's a bunch of phase transitions that

we like to talk about that happened over the course of the evolution of life. One such transition

was the origin of eukaryotes, right? Eukaryotes are cells that had nuclei in them. And we think these

days that that came about from two different kinds of cells getting together, joining together,

sharing their DNA, distributing it in the cell in interesting ways. You have mitochondria,

and then you have the nuclear DNA. And it's all a big part of the interesting kinds of life we have

on Earth. I shouldn't say interesting. It's all interesting. The complex kinds of life we have on

Earth. Eukaryotes compared to prokaryotes, which don't have nuclei, have a lot more capacity, a

lot more potential for being complex, such as being multicellular. And once you go from a single

cell to organism to a multicell organism, then the possibilities of complexity grow enormously.

So today's guest, Will Ratcliffe, is a biologist who is one of the world's experts on exactly this

transition from unicellularity to multicellularity in the evolution of life. Not just studying what

happens there in the record of actual life on Earth, but doing artificial evolution, or what some

people call directed evolution, doing an experiment in the lab where he takes the group, take yeast

cells, and they let them evolve. They give a little bit of selection pressure to grow bigger,

and they say, you know, they don't poke in there the DNA, they just let mutations happen and watch

what happens to these initially unicellular yeast organisms. And what happens very quickly is they

become multicellular. You know, in some sense, which we'll hopefully try to make clearer in the

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