Accumulation of deleterious mutations and fitness in a pre-industrial human population Adam D. Hayward, Virpi Lummaa, Georgii A. Bazykin Many of the mutations are detrimental to fitness, and each individual carries a burden of deleterious mutations that were accumulated over many generations. In humans, the number of de novo point mutations passed on to an offspring is strongly dependent on the father's age. Here, we use extensive pedigree data on a pre-industrial Finnish population to get, for each individual, the ages of his or her male ascendants for up to three generations, and use this data as a proxy for the number of acquired mutations. Individuals whose fathers, grandfathers and great-grandfathers fathered their lineage at age of 20 were 9% more likely to survive to adulthood than those with 40-year-old male ancestors. Among survivors to adulthood, older male ascendants were also associated with a reduced probability of getting married. These observations suggest that the deleterious mutations acquired from recent ancestors may be a substantial burden to fitness in humans.