The Discovery of Evolution and Evolutionary Processes

Background: The Plenum. The geologists first embraced the idea of geological time and of a world that gradually came to assume its current form. Biologists were aware of their work and its implications for their field, but were constrained by theological doctrine.

Whereas Bishop Ussher actually had to perform research and make logical inferences in order to draw his conclusions about the age of the Earth, anyone who wondered about the mutability of living things, had only to read Ecclesiastes 3:14 to be set straight:

"3:14 I know that, whatsoever God doeth, it shall be for ever: nothing can be put to it, nor any thing taken from it...."

"3:15 That which hath been is now; and that which is to be hath already been; and God requireth that which is past. "

From this emerged the notion of the Plenum [Latin "fullness"], maintaining that:

Thusorganismal extinction was contrary to the Bible. Indeed, many early paleontologists such as Thomas Jefferson assumed that living specimens of the animals whose remains they were finding must exist somewhere.

Extinctons: The concept of the plenum received a one-two punch.

The notion of the plenum was refuted. To this refutation was added the discovery of Geologic Time around the turn of the 19th century. At this point, biologists openly contemplated the idea of organismal evolution.

Evolution: Definition: Before proceeding, evolution = "Descent with modification". The central tenet of the theory of evolution is, "The diversity of living things is the product of descent with modification." Note that this definition says nothing about how evolution occurs. Evolution is foremost a pattern. Before we discuss it, let's mention...

The reality of the pattern of evolution.

Prior to the discovery of geological time, it was reasonable to assume that all organisms had appeared recently. Since there had not, it was thought, been enough time for organisms to accumulate a serious history, the idea that their form reflected their history was meaningless.

Imagine US history compressed into one week.

The discovery of geological time, however, added an extra dimension to the organization of organismal form. Specifically, when fossil and living organisms were organized according to their similarity of form and their occurance in time, it began to seem as if lineages had slowly been modified through time, and even as if different lineages had branched from the same ancestor. Indeed, as soon as geological was discovered, biologists began speculating that species had evolved, ie, has been modified during their descent. Even biologists like Louis Agassiz, who openly rejected evolution couldn't help but organize the history of organisms in a suggestive way.

The pattern of evolution was readily visible to many investigators by the early 19th cent. All it took was the recognition of geological time, and some familiarity with the fossil record. The problem was that no one could propose a convincing mechanism by which this might happen. Several people tried, but were unable to propose anything that did not at some point resort to unfalsifiable propositions.

Jean Baptiste Lamarck, who proposed that "driving forces of nature" impelled organisms toward "improvement".

Problem: the driving force was unmeasurable (indeed, there was no physical evidence to suggest that it existed) , and the definition of "improvement" was subjective, so Lamarck's ideas didn't make much headway. Nevertheless, people were searching, and the stage was set for a major intellectual revolution. It was a matter of time before someone put it all together.

How it happened: Charles Darwin (1809-1882)

Darwin received a strong religious upbringing and was slated for a church career, however his poor study habits and lack of focus caused his father to diagnose him as a young man who needed time to think things over. In 1839 he obtained an unusual job: "Captain's companion" for the captain of the naval research vessel HMS Beagle. (Not a standard position. Capt. Robert FitzRoy, himself a capable naturalist, had a tendency toward severe depression which was made worse by the isolation of life at sea. To make life more pleasant, he hired Darwin to simply be his confidante) Darwin took advantage of the opportunity to become a proper naturalist. His three year voyage around the world changed his life and set the stage for his later career. (cf. The Voyage of the Beagle, Charles Darwin for a highly readable account).

Before departure, Darwin purchased a copy of The Principles of Geology by Charles Lyell (a student of James Hutton). This book advanced Hutton's idea of uniformitarianism, i.e. that the geological processes that we observe today are the same ones that have been active in the past ("The present is key to the past") . Darwin read it on the way to South America. There, he encountered the fossils of ancient unknown mammals. By the time the Beagle reached the Galápagos Islands, Darwin seems to have been thinking about uniformitarianism in a biological context. On the Galápagos, (Geologically young volcanic islands) he noted paradoxes:

Back in England, Darwin encountered the ideas of Thomas Malthus on reproductive excess. Malthus noted that generally human populations left unchecked increased exponentially while the resource base on which they depended increased linearly.

What resulted was not a stable situation and one had only to look at human history to see how cruelly these two accounts were balanced. Of course, what was true for humans might also be true in nature.

No one knows when the lightbulb appeared above Darwin's head, but by 1842, he had begun a notebook on the "transmutation of species". And yet, for 24 years after the voyage, he kept the idea to himself.

He was not idle during this time. Note also that Darwin wasn't an intellectual lightweight. Had he never published on evolution, he would have made it into the history books on the basis of his work on marine biology and the geology of coral atolls.

Darwin, seems to have wanted to publish a large work on evolution late in life, to be his "crowning achievement". Problem: I said before that the evolutionary intellectual revolution was waiting for someone to connect the dots. If Darwin wouldn't do it, someone else would.

In fact, in 1858, Alfred Russell Wallace, a naturalist stationed in Indonesia, wrote to Darwin, asking his opinion of some new ideas that he had. Darwin was alarmed to see that Wallace had independently reached the same conclusions he had about evolution. The two agreed to co-author a small paper in 1858.

In 1859, Darwin hastily published The Origin of Species by Means of Natural Selection, or the Preservation of favored Races in the Struggle for Survival. (AKA The Origin of Species). First edition sold out first day.

In the Origin, Darwin advanced two concepts.

These were illuminated by a large volume of observations.

By the time of his death (1882), the academic community had largely been won over.


What evolution is not: