This open access paper uses historical data to argue that differences in human mitochondrial DNA (mtDNA) lead to differing health and longevity benefits in response to calorie restriction: "We chose to focus on haplogroup H, which is one of the more recent haplogroups, but also now the most prevalent European mtDNA haplogroup, and compare historical longevity in closely related haplogroup U individuals under extremes of caloric intake. ... The human population has undergone dramatic shifts in caloric intake during different time periods throughout the last 200 years. ... We see an expected general increase in longevity during the 20th century in both haplogroups. Before 1920 there is no significant difference between the longevity of individuals in haplogroup H and U. During the caloric restriction of the Great Depression, 1920-1940, haplogroup H shows significant increase in longevity compared to haplogroup U [with a] mean difference [of] 2.6 years." A very clever analysis; the researchers go on to use computer modeling to theorize on how a specific single nucleotide polymorphism difference between the haplogroups produces this longevity difference.