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About Deby L. Cassill

Darwin’s “applied to the family” hypothesis spawned a number of models that attempted to explain the evolution of altruistic offspring including kin selection, reproductive skew and bet-hedging models. The unspoken assumption central to these models was that offspring were initially created equal; differences in the fertility of adults emerge from transactions such as altruistic “giving,” or coercive “taking” Dr. Cassill has developed a maternal investment model that departs from an assumption of offspring equality and instead proceeds with an assumption of offspring inequality. In short, right from the beginning, “Moms don’t pack their kids’ lunch boxes equally,” (M. Ghiselin, personal communication). An assumption of inequality alters the solution to the enigma of Darwin’s altruistic “neuters” from a moral question, “Why do some offspring give up their reproductive rights?” to a risk- management question, “In risky environments, how many disposable spares must a matriarch invest in to ensure the survival of two sexually mature heirs, one to replace her and one to replace her mate?”  Currently, Dr. Cassill’s research is focused on gathering field data to test the assumptions and predictions of her maternal risk-management model on the evolution of diversity “within” species from bacteria to mammals.


Present Associate Professor, Associate Chair, University of South Florida St. Petersburg


  • ZOO 4513C (Animal Behavior)
  • ZOO 4512 (Sociobiology)
  • BSC 3402L Experimental Biology Lab (Research Methods)
  • BSC 4910 (Undergraduate Research)


Ph.D., Florida State University ‐ Biology
M.S., Florida State University ‐ Biology
M.P.A., University of West Florida
B.S., Florida State University ‐ Biology
B.A., University of Iowa

Contact Information

Phone: (727) 873-4064 (O), or (727) 873-4832 (Lab)


Peer Reviewed Articles (36)