Molecular Clock

“Sequences accumulate changes, but the biological clock does not tick at one speed on every branch.”

01 / PLAINLY

What it means, plainly

Molecular clocks estimate divergence times from genetic changes calibrated against other evidence.

02 / CONTEXT

A little more

A clock combines sequence differences, an evolutionary model, and calibrations such as fossils or geological events. Rates vary across genes, lineages, and eras, so dates carry intervals.

03 / WHY IT MATTERS

Why it matters

It helps date splits not preserved directly as fossils and requires independent evidence to work together.

04 / EXAMPLE

A familiar example

Differences among genes with estimated rates let a model calculate when two lineages shared an ancestor.

05 / LIMIT

What it does not mean

Differences cannot simply be divided by one universal rate; a strict clock biases dates when rates vary.

06 / NOTICE

Notice it in your day

Imagine two clocks that gain time differently. List the calibration points needed to reconstruct an earlier hour.

FINAL NOTE

The idea worth keeping

Inspect sequences, model, calibrations, and interval width before repeating an evolutionary date.

QUESTIONS / 02

Questions people still have

Do genes change at a constant speed?

No. Some rates are roughly stable in limited contexts, but they vary among genes, species, and periods.

Do molecular clocks make fossils unnecessary?

No. Fossils and other dated events calibrate clocks and help test whether their estimates are plausible.