How do we know the age of the last common ancestor shared by two species?

Verified step by step guidance

1. Understand that the age of the last common ancestor (LCA) shared by two species is estimated using molecular data and fossil records, which provide information about evolutionary divergence times.
2. Collect genetic sequence data (such as DNA, RNA, or protein sequences) from both species to compare their similarities and differences.
3. Calculate the genetic distance between the two species by determining the number of molecular changes or mutations that have accumulated since their divergence.
4. Use a molecular clock model, which assumes a relatively constant rate of genetic mutations over time, to convert the genetic distance into an estimate of divergence time. The basic formula is: \[\text{Divergence Time} = \frac{\text{Genetic Distance}}{2 \times \text{Mutation Rate}}\] where the factor 2 accounts for mutations accumulating independently in both lineages.
5. Calibrate the molecular clock using fossil evidence or known geological events to improve the accuracy of the estimated age of the last common ancestor.

Key Concepts

Molecular Clock

The molecular clock is a method that estimates the time of divergence between species by measuring the number of genetic mutations accumulated over time. It assumes mutations occur at a relatively constant rate, allowing scientists to infer the age of the last common ancestor based on genetic differences.

Phylogenetic Trees

Phylogenetic trees are diagrams that depict evolutionary relationships among species based on genetic or morphological data. By analyzing branching patterns and genetic distances, researchers can identify common ancestors and estimate when species diverged from one another.

Fossil Record and Calibration

The fossil record provides physical evidence of past organisms and helps calibrate molecular clocks by offering minimum age estimates for divergence events. Combining fossil data with genetic information improves accuracy in dating the last common ancestor of species.