Histone tales: echoes from the past, prospects for the future

It has been 150 years since Charles Darwin described in his seminal work On the Origin of Species how descent with modification and natural selection could explain the diversity of life. When Mendel's theory of inheritance was rediscovered in the early 1900s and verified to be consistent with natural selection, evolutionary biologists adopted genetics as the central pillar of the Modern or Neo-Darwinian Syntheses and committed to genetics as the center of their explanatory paradigm. With Darwinism becoming widespread, the discovery of the DNA double helix structure by Watson and Crick was hailed as finally delivering the long-sought hereditary mechanisms for evolutionary theory.The concentration on genetics has now lasted almost a century and, despite some claims to the contrary, evolutionary genetics established the consistency, though not the sufficiency, of genetics and natural selection to explain evolution. We are now coming to realize that gene-centric theories of evolution are limited in their scope [1,2]. This shortcoming has been addressed by the life history theory, which analyzes the evolution of whole-organism traits (in particular phenotypic variations such as size at birth, growth rates, age and size at maturity, clutch size and reproductive investment, mortality rates and lifespan) on the basis of the criteria that life histories are shaped by the interaction of extrinsic and intrinsic factors. It states that extrinsic factors are ecological impacts on survival and reproduction and that intrinsic factors are tradeoffs among life history traits and lineage-specific constraints on the expression of genetic variation.Although life history theory can offer detailed answers to the question of why phenotypes are different, it does not attempt to understand the mechanisms that mediate and integrate these differences. Three recent studies [3-5] take us, however, an important step forward in this direction. They build on the nematode Caenorhabditis elegans as