Human evolution has been associated with drastic changes in environment and lifestyle over time, with each of these changes resulting in selective pressures (Voight et al., 2006). Natural selection is the differential reproductive success of genetically distinct individuals or genotypes within a population. Strongly deleterious mutations will rapidly be eliminated from populations, whereas strongly positive mutations will quickly rise to fixation leading to changes in allele frequency over time. This process leaves signatures on the genome which can then be detected (Sabeti et al., 2006).

Epigenetics refers to heritable changes outside of the DNA sequence itself and provides a potential mechanism by which environmental and lifestyle exposures can impact gene expression over the course of a lifetime. Epigenetic mechanisms can include DNA methylation and histone modifications. DNA methylation is the most widely studied epigenetic change and involves the addition of methyl groups to nucleotide bases (Vocht et al., 2018).

Natural selection is a long term, multigenerational response to environmental factors that can influence the role of genes in human traits (Bamshed and Wooding, 2003) whereas epigenetic inheritance allows stable changes in DNA methylation to be passed from one generation to the next (Feil and Fraga, 2012). Both selection and methylation act in response to environmental exposures but over different timescales. This project will aim to unravel the interplay between selection and methylation to assess whether DNA methylation offers a mechanism to respond to exposures in the short term which may eventually lead to changes in allele frequency.

References
1. Bamshad, M. & Wooding, S.P. Signatures of natural selection in the human genome. Nature Reviews Genetics 4, 99-111A (2003).
2. de Vocht, F. et al. DNA methylation from birth to late adolescence and development of multiple-risk behaviours. Journal of Affective Disorders227, 588-594 (2018).
3. Feil, R. & Fraga, M.F. Epigenetics and the environment: emerging patterns and implications. Nature Reviews Genetics 13, 97-109 (2012).
4. Sabeti, P.C. et al. Positive natural selection in the human lineage. Science 312, 1614-1620 (2006).
5. Stearns, S.C., Byars, S.G., Govindaraju, D.R. & Ewbank, D. Measuring selection in contemporary human populations (vol 11, pg 611, 2010). Nature Reviews Genetics 12, 1 (2011).
6. Voight, B.F., Kudaravalli, S., Wen, X.Q. & Pritchard, J.K. A map of recent positive selection in the human genome (vol 4, pg 154, 2006). Plos Biology 4, 659-659 (2006).