Abstract: The problem of inferring history from genetic data is complex and underdetermined; there are many possible scenarios that would explain the same data. It can be made more tractable by making reasonable simplifications to the model, but it is continually important to remember what has been demonstrated and what is merely a parsimonious working assumption. In this paper we have chosen to model the demographic ancestry of humanity using the simplest of assumptions, with a homogeneous population whose size can vary over time. All other assumptions such as the mutation rates were standard, and no natural selection was in operation. Using a previously published backwards simulation method and some newly developed and faster algorithms, we run our single-couple origin Read More ›
If you asked pretty much any population geneticist about human origins they would say, “All the evidence says the effective population size has never been below several thousand.” That’s certainly what Dennis Venema thought, and said most emphatically. Read More ›
by Justin Taylor on October 28, 2019 at The Gospel Coalition A significant new study has just been published, showing that it is scientifically possible—contrary to what is often claimed—that human beings descend from a single human couple: Ola Hössjer and Ann Gauger, “A Single-Couple Human Origin Is Possible,” BIO-Complexity 2019 (1):1– 20. Here are the authors of the piece: Ola Hössjer is professor of mathematical statistics at Stockholm University, Sweden. He has done research in statistics and probability theory with applications in population genetics, epidemiology, and insurance mathematics. Hössjer is the author of 85 peer-reviewed papers, has supervised 13 PhD students, and in 2009 he received the Gustafsson prize in mathematics. Ann Gauger is a senior research scientist at Biologic Institute. Her Read More ›
The publication of our new BIO-Complexity paper, “A Single-Couple Human Origin Is Possible,” announced here on Monday, is actually the culmination and continuation of the work of several people. I do not want to leave the impression that the work by my co-author Ola Hössjer and myself was done in isolation. Far from it! We began the modeling project in earnest in 2014 and published the first model in 2016, but in 2017 some very interesting events took place, described below. What follows is an updated version of a post I wrote on March 5, 2018. Read More ›
Haplo has a large number of parameters. Two of those describe how the population reproduces. There is one parameter, alpha, a which controls variablility of fertility, and another, beta, which controls rates of monogamy. One interesting concept in population genetics is that these two parameters can be fudged together with the real population size, into an effective population size. Here is an intuitive / visual example of why that works.
All mutations start as single copy-errors but some of them increase in the population by random processes. Random differences in reproductive success cause some lineages to branch, and others to go extinct. Mutations are presumed to happen randomly at a more-or-less constant rate and accumulate as they are inherited by descendants. See the figure below. Each row represents a generation, with the present at the bottom, and each ball is a chromosome. The colored dots are different mutations or Single Nucleotide Polymorphisms (SNPs) the chromosome carries. The links from generation to generation show the ancestral lineage of each chromosome going back in time. Mutation and Genetic Drift Usually people think of generations as growing forward in time, with twigs coming Read More ›