A founder effect happens when a small group splits off from a larger population and carries only a small portion of the original genetic diversity. Over time, rare alleles in the founders can become common simply because they were present in that small group. A population bottleneck works in the opposite direction. When a large population suddenly shrinks, for example due to disease, climate change, or migration, its genetic diversity collapses. Ancient DNA studies have documented both patterns. Research on early farming communities in Europe, for example, has shown repeated bottlenecks as small groups moved into new regions carrying limited genetic variation. These events left signatures such as reduced heterozygosity and shifts in allele frequency that are still detectable thousands of years later.
Seeing Evolution Through Time
Ancient DNA makes evolution feel less abstract. Human genomes reveal slow shifts across many generations. Microbial genomes show rapid changes across a few years or decades. By comparing ancient and modern DNA, both human and pathogen, we can watch natural selection operate on different timescales and see how these interactions influenced real historical events, from epidemics to migrations. Each of these small pieces of the puzzle can inform archaeologists and historians about what was happening in the past, and how all of these factors come together to make history.
