The evolution of animal cell motility.

Eukaryotic cells use a number of diverse mechanisms to swim through liquid or crawl across solid surfaces. The two most prevalent forms of eukaryotic cell motility are flagellar-dependent swimming and actin-dependent cell migration, both of which are used by animal cells and unicellular eukaryotes alike. Evolutionary cell biologists have used morphological and molecular phenotypes to trace the evolution of flagellar-based swimming. These efforts have resulted in a large body of evidence supporting a single evolutionary origin of the eukaryotic flagellum, an origin that dates back to before the diversification of modern eukaryotes. Actin-dependent crawling, in contrast, involves mutiple distinct molecular mechanisms, the evolution of which is just beginning to be explored.