How do molecular clocks help in studying evolution?

Molecular clocks help in studying evolution by estimating the time of divergence between different species based on genetic mutations.

Molecular clocks are a key tool in the field of evolutionary biology. They are based on the concept that genetic mutations occur at a relatively constant rate over time. By comparing the genetic sequences of different species, scientists can estimate the number of mutations that have occurred since they last shared a common ancestor. This allows them to estimate the time of divergence, or when the species began to evolve separately.

The concept of the molecular clock was first proposed in the 1960s by Emile Zuckerkandl and Linus Pauling. They observed that the number of differences in the amino acid sequences of a specific protein between different species was proportional to the time since they diverged from a common ancestor. This suggested that mutations in the genetic code occur at a relatively constant rate, like the ticking of a clock.

Molecular clocks are particularly useful in studying the evolution of species for which there is little or no fossil record. They can also help to resolve disagreements between different methods of dating evolutionary events. For example, if the fossil record suggests that two species diverged at a certain time, but the molecular clock suggests a different time, this can prompt further investigation to resolve the discrepancy.

However, it's important to note that molecular clocks are not perfect. The rate of mutation can vary between different species, and even between different parts of the genome within a single species. Environmental factors can also influence the rate of mutation. Therefore, molecular clock estimates are usually given with a range of uncertainty.

Despite these limitations, molecular clocks have greatly enhanced our understanding of evolutionary history. They have been used to estimate the time of divergence of major groups of organisms, such as the separation of birds and mammals, and the emergence of humans as a distinct species.