Ongoing Projects
The HOMINID Project
The Siberian Native Population Project
The Austronesian Societies Project
Past Projects
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Our Research
Over the last decade, my lab has pursued studies of variation on
the Y chromosome as a model system to explore human evolution. Now the lab is
comparing patterns of genetic variation on the Y chromosome, mitochondrial DNA,
X chromosome, and autosomes to distinguish the genomic footprint of natural
selection from the signatures of demographic processes. We are engaged in a
long-term collaborative project with scientists at UCSF to gather new data and design novel analytical methods to answer long-standing questions in human evolution.
One focus of this research is on the evolutionary relationships of "archaic" human groups (such as the Neanderthals in Europe and Homo erectus in Asia) to modern humans. Did archaic forms make any contribution to the contemporary human gene pool, or were Neanderthals and H. erectus completely replaced (without interbreeding) by modern humans as they expanded out of Africa within the last 100 thousand years? Did our ancestors make the transition to modern form in a small, isolated part of Africa , or over a broader geographic range with genetic contributions from divergent populations?
Another focus of this research is on human population growth. Although our current population size is more than 6 billion, the long-term average population size was probably substantially less than 1 million. When did human populations begin to expand dramatically in size? Was this growth associated with a particular event in human history, such as the advent of language or the invention of agriculture? Our study design of 90 loci encompassing ~1.5 Mb on the autosomes and the X chromosome in 90 humans will reveal patterns of linkage disequilibrium and further our understanding of how and why recombination rates vary across the genome.
Members of the Hammer Lab are also interested in identifying regions of the genome that have been shaped by natural selection. One study focuses on the role that natural selection has played in shaping pigmentation variation across the human species. By examining patterns of variation in 11 pigmentation candidate loci sequenced in the Hominid Panel we hope to better understand the roles that purifying and positive selection have played in determining the distribution of pigmentation levels across different UVR environments while at the same time controlling for demographic history. This project is exploring questions relating to the convergent evolution of similar skin pigmentation phenotypes across populations inhabiting comparable UVR environments as well as addressing the timing and strength of selection on favored haplotypes.
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