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Science 1 November 2002:
Vol. 298. no. 5595, p. 919
DOI: 10.1126/science.298.5595.919i
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This Week in Science

The evolution of complex organs such as eyes or placentas presents a dilemma because they demand a large number of individual adaptations to function property, so it can be difficult to envision how they could all fall into place. The live-bearing fish genus Poeciliopsis displays a continuum of placental development, which ranges from little or no provisioning (yolk feeding) to more extensive maternal provisioning, that allows evolution of this organ to be studied. Reznick et al. (p. 1018; see the news story by Morrell) show that there have been three independent origins of extensive maternal provisioning in the genus. The upper estimates for the evolution of extensive postfertilization provisioning range from 0.75 to 2.34 million years. Such relatively rapid evolution has been predicted in theoretical models.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)