“…Several lines of evidence suggest heritability of and natural selection on yolk hormone concentrations. Field and laboratory studies with wild birds showed that yolk androgen concentrations are heritable and under natural selection (Ruuskanen et al, ; Tschirren, Sendecka, Groothuis, Gustafsson, & Doligez, ); directional selection for high or low yolk androgen concentrations in domesticated Japanese quail ( Coturnix japonica ) yielded rapid divergence of titers within a few generations (Okuliarova, Groothuis, Škrobánek, & Zeman, ) and indicates matrilineal inheritance (Tschirren et al, ) ; and artificial selection for behavioral traits such as bold and shy personalities in Great tits ( Parus major ) resulted in increasing, respectively, decreasing yolk androgen concentrations over the laying sequence (Groothuis, Carere, Lipar, Drent, & Schwabl, ). These results prompt us to propose that differential environments operating in urban versus rural populations lead to coupled changes in yolk androgen concentrations and behavior, the mechanistic link being the wide‐spread and well‐established organizational actions of steroid hormones on brain function during development of vertebrates (Adkins‐Regan, ; Fowden & Forhead, ; McCarthy, ; O'Connor & Barrett, ).…”