Timeline of dating
As this happens every generation, segments inherited from a particular individual get broken into smaller and smaller chunks.Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor.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.However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case.Comparison of DNA between you and your sibling would show relatively few mutational differences because you share ancestors – mom and dad – just one generation ago.However, there are millions of differences between humans and chimpanzees; our last common ancestor lived over six million years ago.
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.
In a single human genome, there are about 70 nucleotide changes per generation – minuscule in a genome made up of six billion letters.
But in aggregate, over many generations, these changes lead to substantial evolutionary variation.
Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.
Mutations are changes to the letters of DNA’s genetic code – for instance, a nucleotide Guanine (G) becomes a Thymine (T).
Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes.