PORT TOWNSEND — Seismologist and author Rob Wesson will delve into the history of Charles Darwin at 4 p.m. Saturday.

The lecture will be at Quimper Unitarian Universalist Fellowship, 2333 San Juan Ave. Although it is free to the public, a $5 donation would be appreciated to defray the speaker’s travel expenses.

Wesson will go beyond the obvious.

Darwin is known as the father of the theory of evolution and the man who altered humanity’s view of man’s place in the world.

What many don’t know is that Darwin was onboard the HMS Beagle as a geologist — on a mission to examine the land, not flora and fauna. He had a seminal role in exploring and explaining the ups and downs of Earth’s crust.

This story, detailed in Wesson’s new book, “Darwin’s First Theory,” is the one he will share with the audience.

Retracing Darwin’s footsteps, Wesson trekked across the Andes, cruised waters charted by the Beagle, hunted for fossils in Uruguay and Argentina, and explored sites of long-vanished glaciers in Scotland and Wales.

Upon Darwin’s return from his five-year journey aboard the Beagle — and after examining the effects of earthquakes, tsunamis and volcanic eruptions — he conceived his theory of subsidence and uplift — his first theory.

Growing up in the Pacific Northwest, Wesson became fascinated by mountains and glaciers, an interest that led to an undergraduate degree in earth science from MIT, and master’s and doctorate in geophysics from Stanford University.

His career in earthquake research with the U.S. Geological Survey spans four decades.

In retirement, his research has focused on Chile, where he is collaborating with a team exploring large earthquakes, tsunamis and associated tectonic questions, work supported in part by grants from the National Science Foundation.

When not traveling in South America or elsewhere, Wesson divides his time between his home in Evergreen, Colo., and the rustic cabin he built near McCarthy, Alaska.