The paper by Mousseau and Roff examines the heritability of traits closely associated with fitness in wild, outbred animal populations. Using 1120 narrow-sense heritability estimates from 75 species, they find that life history traits generally have lower heritabilities than morphological traits, while behavioral and physiological traits fall in between. These findings support popular interpretations of Fisher's Fundamental Theorem of Natural Selection and Falconer's work, suggesting that high heritabilities are maintained within natural populations even for traits under strong selection. The study also reveals that the heritability of morphological traits is significantly lower in ectotherms compared to endotherms, possibly due to the strong correlation between life history and body size in many ectotherms. The authors conclude that while traits closely associated with fitness tend to have lower heritabilities, significant genetic variance is maintained in natural populations, highlighting the need for further research into the mechanisms behind this phenomenon.The paper by Mousseau and Roff examines the heritability of traits closely associated with fitness in wild, outbred animal populations. Using 1120 narrow-sense heritability estimates from 75 species, they find that life history traits generally have lower heritabilities than morphological traits, while behavioral and physiological traits fall in between. These findings support popular interpretations of Fisher's Fundamental Theorem of Natural Selection and Falconer's work, suggesting that high heritabilities are maintained within natural populations even for traits under strong selection. The study also reveals that the heritability of morphological traits is significantly lower in ectotherms compared to endotherms, possibly due to the strong correlation between life history and body size in many ectotherms. The authors conclude that while traits closely associated with fitness tend to have lower heritabilities, significant genetic variance is maintained in natural populations, highlighting the need for further research into the mechanisms behind this phenomenon.