The article by R. Frankham examines the genetic variation in island populations compared to mainland populations and its implications for extinction rates. The study analyzes published data on genetic variation in allozymes, nuclear DNA markers, mitochondrial DNA, inversions, and quantitative traits in island and mainland populations. The results show that a significant majority of island populations (165 out of 202 comparisons) have lower genetic variation than their mainland counterparts, with an average reduction of 29%. This trend is more pronounced in island endemic species, which show lower genetic variation than related mainland species in 34 out of 38 cases. The magnitude of differences is related to dispersal ability, with species that cannot fly showing proportionately less reduction in heterozygosity. The study concludes that genetic factors contribute to the higher extinction rates of island populations, as they have reduced evolutionary potential due to lower genetic variation.The article by R. Frankham examines the genetic variation in island populations compared to mainland populations and its implications for extinction rates. The study analyzes published data on genetic variation in allozymes, nuclear DNA markers, mitochondrial DNA, inversions, and quantitative traits in island and mainland populations. The results show that a significant majority of island populations (165 out of 202 comparisons) have lower genetic variation than their mainland counterparts, with an average reduction of 29%. This trend is more pronounced in island endemic species, which show lower genetic variation than related mainland species in 34 out of 38 cases. The magnitude of differences is related to dispersal ability, with species that cannot fly showing proportionately less reduction in heterozygosity. The study concludes that genetic factors contribute to the higher extinction rates of island populations, as they have reduced evolutionary potential due to lower genetic variation.