A sex skew in life-history research: the problem of missing males

Life-history strategies are diverse. While understanding this diversity is a fundamental aim of evolutionary biology and biodemography, life-history data for some traits-in particular, age-dependent reproductive investment-are biased towards females. While other authors have highlighted this sex skew, the general scale of this bias has not been quantified and its impact on our understanding of evolutionary ecology has not been discussed. This review summarizes why the sexes can evolve different life-history strategies. The scale of the sex skew is then discussed and its magnitude compared between taxonomic groups, laboratory and field studies, and through time. We discuss the consequences of this sex skew for evolutionary and ecological research. In particular, this sex bias means that we cannot test some core evolutionary theory. Additionally, this skew could obscure or drive trends in data and hinder our ability to develop effective conservation strategies. We finally highlight some ways through which this skew could be addressed to help us better understand broad patterns in life-history strategies.

Automated summary

Life-history strategies exhibit diversity, but there is a bias towards females in life-history data, particularly in age-dependent reproductive investment. This bias has not been quantified, and its impact on our understanding of evolutionary ecology has not been extensively discussed. This review examines the reasons why sexes can evolve different life-history strategies, quantifies the scale of the sex skew, and discusses its consequences for evolutionary and ecological research. The bias hinders our ability to test core evolutionary theories and develop effective conservation strategies, and may obscure or drive trends in data.