St. George Jackson Mivart and the Archaeopteryx

This is St. George Jackson Mivart, and he ruffled the feathers of proponents of every side of the evolution debates of the 19th century. The second slide is a fossil of a ancient species called Archaeopteryx, and its ruffled feathers were at the center of evolutionary debates of the 19th century.

Mivart was raised Anglican but converted to Catholicism (offending group #1). Then he became enamoured of theories of evolution, engaging with some of the most important names in the field — before he decided Darwinian ideas were bunk and published _On the Genisis of Species_ to refute them (offending group #2). Later in life he published documents denounced by the Catholic Church (group #3). The guy couldn’t win. And even though his ideas were taken seriously by Darwin, he was ultimately incorrect.

Mivart’s big complaint against evolution was that the function of certain organs can’t develop half-baked — how can you have no eyesight and then have some naturally selected proficiency with vision? Or lungs? Or feathers? How can you go from flightless to slightly feathered without an external force driving for the step of flight?

Enter Archaeopteryx, discovered in 1861. As you can see, it looks reptilian (it is actually closer to a dinosaur), but has feathers. Darwin et al.’s excitement at this fossil can be understood– it seemed to be a “transitional species” halfway between dinosaur and bird. Mivart’s question still needed better answering, though. And the answer came from Darwin himself, who wrote that “a change of function” accompanies the incipient organs of species who later evolve more complex expressions. That means that feathers first developed not for flight, but perhaps warmth. Eyes came from primitive light-sensors. Lungs from air-sacs that promote buoyancy.

The idea that organs develop for one purpose but evolve a radically different function has been a linchpin in understanding how evolution works.