Evidence for human variation and adaptation

Lachance et al. (2012)

BIOL 1510 Group B23:Sara EndresYoon Sik Lee

Mathew MartiniNathaniel Robinson

IntroductionObjective: To find the evolutionary history of

the hunter-gathers by analyzing five males of each population including Pygmies from Cameroon, Khoesan-speaking Hadza and Sandawe from Tanzania for understanding the genetic diversity of humans, the allelic spectrum of genetic variation, and the origin of modern humans.

Whole Genome Sequencing & Functional Classification of VariantsEvolutionary process:

• Deletions > insertions• Benign > damaging alleles• Bottlenecks from migration: influence on

Europeans (Lohmueller 2008)[1]

• Supports ancient divergence of tribesResearch Methods:

• Operational definition: novel variants• Technology - quality control• Compared published results• Whole genome sequencing - global context

Marginal error

Population Genetics of Functionally Important Regions of the Human Genome

An increase in the frequency of rare alleles in genetic regions occured for the populations (can be explained by selective sweeps and purifying selection)

Demographic History of African Hunter-GatherersPopulation sizes•Pygmies- 11,300–25,700•Hadza- 9,200–20,900 •Sandawe- 10,600–24,000Proportion of polymorphic sites•Highest for Pygmies•Lowest for Hadza•Low frequency alleles are present in higher than expected proportions for Pygmies and

Sandawe but are lower for Hadza. => Had traits that were not expected.

"The 5 Pygmies sequenced share a set of 44 gene variants on chromosone 3 that are very rare in other African populations and are absent in asians and europeans." (Callaway 2012)[3]

This shows how unique the pygmy populations became.

Ancestry Informative Markers (AIMs)• Variant allele frequencies are greater

than 50% in 1 group, but nonexistent in the other 2 groups

• Result of population-specific adaptation• AIMs are the cause of short stature in

the Pygmies (Mendizabal 2012)[2]

ConclusionAccording to the results, some traits hold

a significant role in defining hunter-gatherer populations' immunity, reproduction, metabolism, and height. This study has greatly expanded and deepened the knowledge of human genome variations and shows that the isolation of African native tribes has produced significant evolutionary changes.

References[3]Callaway, Erin. "Hunter-gatherer Genomes a Trove of Genetic

Diversity." Nature.com. Nature Publishing Group, 26 July 2012. Web. 11 Sept. 2012. <http://www.nature.com/news/hunter-gatherer-genomes-a-trove-of-genetic-diversity-1.11076>.

Lachance, et al., Evolutionary History and Adaptation from High-Coverage Whole-Genome Sequences of Diverse African Hunter-Gatherers, Cell, Volume 150, Issue 3, 3 August 2012, Pages 457-469.

[1]Lohmueller, K. E. (2008). Proportionally more deleterious genetic variation in european than in african populations. Nature, 451(7181), 994-997.

[2]Mendizabal, Isbel, Marigorta M. Urko, Oscar Lao, and David Comas. "Adaptive evolution of loci covarying with the human African Pygmy phenotype." Human Genetics. 131.8 (2012): 1305-1317. Web. 11 Sep. 2012.