Most species are not driven to extinction before genetic factors impact them

Derek Spielman, Barry W. Brook, Richard Frankham*

*Corresponding author for this work

Research output: Contribution to journalArticle

655 Citations (Scopus)


There is controversy concerning the role of genetic factors in species extinctions. Many authors have asserted that species are usually driven to extinction before genetic factors have time to impact them, but few studies have seriously addressed this issue. If this assertion is true, there will be little difference in genetic diversity between threatened and taxonomically related non-threatened species. We compared average heterozygosities in 170 threatened taxa with those in taxonomically related nonthreatened taxa in a comprehensive metaanalysis. Heterozygosity was lower in threatened taxa in 77% of comparisons, a highly significant departure from the predictions of the no genetic impact hypothesis. Heterozygosity was on average 35% lower (median 40%) in threatened taxa than in related nonthreatened ones. These differences in heterozygosity indicate lowered evolutionary potential, compromised reproductive fitness, and elevated extinction risk in the wild. Independent evidence from stochastic computer projections has demonstrated that inbreeding depression elevates extinction risk for threatened species in natural habitats when all other threatening processes are included in the models. Thus, most taxa are not driven to extinction before genetic factors affect them adversely.

Original languageEnglish
Pages (from-to)15261-15264
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number42
Publication statusPublished - 19 Oct 2004

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