The article reviews the phenomenon of transgressive segregation in hybrid populations, where offspring exhibit extreme phenotypes that deviate significantly from both parental traits. The authors analyze 171 studies reporting phenotypic variation in segregating hybrid populations, finding that transgression is common, occurring in 91% of studies and 44% of traits examined. Transgression is more frequent in intraspecific crosses involving inbred, domesticated plant populations compared to interspecific crosses between outbred, wild animal species. Quantitative genetic studies suggest that complementary genes are the primary cause of transgression, although overdominance and epistasis also contribute. The authors discuss the implications of transgressive segregation for adaptive evolution and speciation, arguing that it may provide the raw material for rapid adaptation and niche divergence in hybrid lineages. They also explore predictions about the factors influencing transgressive segregation and highlight the need for further research to understand the genetic basis and evolutionary role of this phenomenon.The article reviews the phenomenon of transgressive segregation in hybrid populations, where offspring exhibit extreme phenotypes that deviate significantly from both parental traits. The authors analyze 171 studies reporting phenotypic variation in segregating hybrid populations, finding that transgression is common, occurring in 91% of studies and 44% of traits examined. Transgression is more frequent in intraspecific crosses involving inbred, domesticated plant populations compared to interspecific crosses between outbred, wild animal species. Quantitative genetic studies suggest that complementary genes are the primary cause of transgression, although overdominance and epistasis also contribute. The authors discuss the implications of transgressive segregation for adaptive evolution and speciation, arguing that it may provide the raw material for rapid adaptation and niche divergence in hybrid lineages. They also explore predictions about the factors influencing transgressive segregation and highlight the need for further research to understand the genetic basis and evolutionary role of this phenomenon.