Timeline how dating has changed
By applying these methods to the ever-growing database of DNA from diverse populations (both present-day and ancient), geneticists are helping to build a more refined timeline of human evolution.
Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.
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Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor.
Gene flow between divergent populations leads to chromosomes with mosaic ancestry.
These changes accrue like the ticks on a stopwatch, providing a “molecular clock.” By comparing DNA sequences, geneticists can not only reconstruct relationships between different populations or species but also infer evolutionary history over deep timescales.
Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species.When scientists say that modern humans emerged in Africa about 200,000 years ago and began their global spread about 60,000 years ago, how do they come up with those dates?Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating.Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events.Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed.