CPSP118G Spring Semester: Earth, Life & Time Colloquium

The Evidence of Evolution

Thomas R. Holtz, Jr.

What is "Evolution?"

Species and Life's Diversity
Naturalists have long noted that there exist units of natural diversity, species, in which the members share certain distinctive features with each other. Following the work of Carl von Linne' (Linnaeus) in the 1700s, species were recognized as one unit within a nested hiearchary of larger clusters of organisms: taxa (singular, taxon; literally, "named thing").

What is a species? That is, what criteria were used to justify whether a population belonged to one or another species.

Linnaeus' "species" were taxa like lions, tigers, black bears, etc. These were assemblages of individuals that share certain attributes:

Later biologists formalized this as "naturally occurring populations that interbreed and produce viable fertile offspring".

Were species fixed: that is, unchanging? Many people thought so:

However, several sets of observations showed that this was not so:

Fixity vs. Transmutation
Traditionally, people accepted the fixity of species just as they accepted that the world today is pretty much the same now as in the past.

Theological argument for fixity under the Biblical concept of the Plenum ("fullness"):

Many early naturalists accepted the Plenum, but evidence of extinction (man-made, as in the dodo, and natural, as in fossils) showed that things could be removed from Creation. What about adding to it?

The discoveries of the early (18th and 19th Century) geologists put paid to the idea that the surface of the Earth was unchanging:


While some thinkers once thought that life as we see it now is the way it has always been, the discovery of the fossil record showed that strange creatures once roamed the Earth that are no longer there. Naturalist John Herschel (in an 1836 letter to Charles Lyell) wrote:

How to explain these observations? Two main possibilities:

Transmutationism, a set of early evolutionary models, accepted by several prominent scientists by the late 1700s. Among them were Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (normally known as Jean Baptiste de Lamarck) and Erasmus Darwin (doctor, scientist, surgeon, abolitionist, and INCREDIBLY rich).

Fossils demonstrated that the living component of the Earth changed through time; shared homologies showed connections between groups; adaptations showed organisms "fit" to their environment. Already accepted the central tenets of Evolutionary Theory:

But what caused the modifications?

Transmutationist models:

Problems with these ideas, however:

Darwin did not discover evolution, nor did its study stop with his work. At least some of the evidence for evolution was long known before his time (although we've added a LOT, even to these lines!)

Initial Evidence for Evolution

Evolution Is:

Last modified: 3 February 2008