Darwin (unit)

The darwin (d) is a unit of evolutionary change, defined by J.B.S. Haldane in 1949. One darwin is defined to be an e-fold (about 2.718) change in a trait over one million years. Haldane named the unit after Charles Darwin.

The equation for calculating evolutionary change in darwins (${\displaystyle r}$) is:

where ${\displaystyle X_{1}}$ and ${\displaystyle X_{2}}$ are the initial and final values of the trait and ${\displaystyle \Delta t}$ is the change in time in millions of years. An alternative form of this equation is:

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