Pluripotent stem cells give hydras impressive regenerative properties.WIKIMEDIA, KRUCZY89The parasitic worm Schistosoma mansoni, which infects millions of people each year, causing diarrhea, malnutrition, and enlarged liver and spleen, relies on stem cells to fuel its long life inside human hosts, according to a study published earlier this year (February 20) in Nature. Parasitic tapeworms also have stem cells, as do the free-living planarian relatives of schistosomes. Indeed, self-renewing cells that can differentiate into the various other tissues of the body have been found in a dizzying array of animals, from primitive sponges and ever-regenerating flatworms to amphibians and mammals.
“[Stem cells] are an invention of multicellular animals,” explained Thomas Bosch, an evolutionary biologist at the University of Kiel in Germany. These cells are integral to reproduction and development, as well as to repairing and renewing tissues over an organism’s lifetime. Furthermore, new research suggests that stem cells may also help some animals adopt radical changes in lifestyle. In the case of planarian flatworms, for example, scientists have recently uncovered evidence that stem cells may have supported the leap from free-living organisms to parasites, and sea squirts appear to have coalesced into colonies and adopted a new style of reproduction thanks to the sharing of somatic stem cells through a shared circulatory system.
Stem cells evolve to meet different organisms’ needs, noted Bosch. Simpler organisms, ...
