The evolutionary ecology of stem cells and their niches – the time is now

During the second set of clinical trials of penicillin in 1942, Howard Florey and his team administered the drug to 15 patients who were considered to be terminally ill with bacterial infections. Fourteen of those patients survived; the one who did not died because the microbe {Streptococcus viridans) causing bacterial endocarditis was thought to have become resistant to penicillin during the course of treatment (Florey and Florey 1943). From in vitro studies, Florey's team were aware that a range of microbes could be resistant to penicillin (Abraham et al. 1941). Alexander Fleming, the discoverer of penicillin, also knew from the use of other drugs how adaptable bacteria were and warned about the development of resistance during his Nobel Lecture in 1945 (Brown 2005, p. 223). To be sure, curing 14 of 15 previous hopeless cases is a great medical achievement. However, as evolutionary ecologists, our responsibility is to think about both short term and long term consequences of our interventions in natural systems. Neither Fleming nor Florey had an evolutionary biologist in their group, but we can imagine that had there been one, the 15th case in which resistance developed would have been of considerable interest. At that time, the observation of Theodosius Dobzhansky that "nothing in biology makes sense except in the light of evolution" was 30 years in the future. But had an evolutionary biologist been there, the history of the last 60 years of development of resistance to antibiotics, herbicides and insecticides might have been very different (Bud 2007). The current enthusiasm for regenerative medicine and associated interest in stem cells both adult and embryonic is based on the assumption that we can remove stem cells from their natural habitat, propagate them in culture, transplant them into a foreign env ronment and assume that the transplanted cells will do as we wish or that we can manipulate them in vivo with desired results (Fuchs et al. 2004). However, there may be enormous differences between what stem cells o in their original niche and what they can do whe put into culture or when transplanted to a new location (Anderson 2001). Raff (2003, p. 16) noted that "perhaps the greatest challenge in stem cell biology is to uncover the ... mechanisms that determine