Summary
Uses the steady rate of neutral mutations to estimate when lineages diverged.
In depth
If neutral substitutions accumulate at a roughly constant rate, the number of sequence differences between species indicates time since divergence once calibrated with fossils. Rates differ between genes and lineages, so relaxed clocks are used.
Zuckerkandl and Pauling proposed the clock in the 1960s from haemoglobin differences. Rates vary between genes, lineages and with generation time, so relaxed clocks allow rate variation and need several calibrations. Synonymous sites and non-coding regions are often used because they are less affected by selection.
The clock indicates that humans and chimpanzees diverged about 6 to 7 million years ago, and that the last common ancestor of all animals lived over 600 million years ago, earlier than most fossil evidence. HIV's clock traces its origin to about 1920 in central Africa.
Remember: a molecular clock gives estimates with errors, and calibrations from fossils set minimum ages.
Frequently asked questions
What is Molecular Clock?
Uses the steady rate of neutral mutations to estimate when lineages diverged.
Which area of biology covers Molecular Clock, and how advanced is it?
Molecular Clock is one of the 53 topics in Evolution. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Common Ancestry, Neutral Theory, Cambrian Explosion.
Can you give an example of Molecular Clock?
Molecular clocks suggest humans and chimps diverged about 6 to 7 million years ago.
What should I learn before Molecular Clock?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Molecular Clock. Intermediate topics assume the Beginner vocabulary.
What topics are related to Molecular Clock?
The closest topics to Molecular Clock are Common Ancestry, Neutral Theory, Cambrian Explosion, Divergent Evolution. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Molecular Clock?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Molecular Clock. To practise the whole of Evolution, use the Evolution quiz.
How is Molecular Clock different from Common Ancestry?
Molecular Clock: Uses the steady rate of neutral mutations to estimate when lineages diverged. Common Ancestry: All living things descend from shared ancestors, evidenced by universal DNA and genetic code. Read both side by side and note what each one explains.
How should I study Molecular Clock step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Common Ancestry and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.