The contemporary evolution of fitness

The rate of evolution of population mean fitness informs how selection acting in contemporary populations can counteract environmental change and genetic degradation (mutation, gene flow, drift, recombination). This rate will influence population increases (e.g., range expansion), population stability (e.g., “cryptic” eco-evolutionary dynamics), and population recovery (i.e., evolutionary rescue). We review approaches for estimating such rates, especially in wild populations. We then review empirical estimates derived from two approaches: mutation accumulation (MA) and additive genetic variance in fitness (IA). MA studies inform how selection counters genetic degradation arising from deleterious mutations; typically generating estimates of <1% per generation. IA studies provide an integrated prediction of proportional change per generation; nearly always generating estimates of <20% and, more typically, <10%. Thus, considerable, but not unlimited, evolutionary potential exists in populations facing detrimental environmental or genetic change. However, further studies with diverse methods and species are required for more robust and general insights.