Here’s a fascinating article on the ways in which groups of cells compete with each other, in a manner somewhat analogous to selection, within multicellular organisms.
https://www.nature.com/articles/d41586-019-03060-y
In the past two decades, an explosion of similar discoveries has revealed squabbles, fights and all-out wars playing out on the cellular level. Known as cell competition, it works a bit like natural selection between species, in that fitter cells win out over their less-fit neighbours. The phenomenon can act as quality control during an organism’s development, as a defence against precancerous cells and as a key part of maintaining organs such as the skin, intestine and heart. Cells use a variety of ways to eliminate their rivals, from kicking them out of a tissue to inducing cell suicide or even engulfing them and cannibalizing their components. The observations reveal that the development and maintenance of tissues are much more chaotic processes than previously thought. “This is a radical departure from development as a preprogrammed set of rules that run like clockwork,” says Thomas Zwaka, a stem-cell biologist at the Icahn School of Medicine at Mount Sinai in New York City.