Species Problem

 

 

Species on Darwin's tree of life

Species and natural selection are the two most common key terms Charles Darwin uses throughout his book entitled The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Surprisingly, however, neither “species” nor “natural selection,” the key terms of the book, are defined in the Glossary, a symptom of evolution’s ongoing “Species Problem.”

Defining “species” became one of Darwin’s great challenges. Darwin recognized that among naturalists of the day, the term “species” did not have a consistent definition. Darwin acknowledged what was accepted at the time –

“No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally, the term includes the unknown element of a distinct act of creation.”

 

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Evolution of Molecular Clocks

 

Michael Ruse, author of the book Defining Darwin, Essays of the History and Philosophy of Evolutionary Biology, concluded that “Indeed, the truth is that there is virtually nothing today in evolutionary studies that correspond exactly to the facts of the Origin.” Molecular clocks are one example.

In the mid-nineteenth century, the idea of molecular clocks was not even remotely considered, not to mention cellular biology or DNA. The scientific revolution had yet to reach into the realm of molecular biology. Case-in-point, Darwin thought “gemmules” learned by parents were passed on to the next generation through a process of “blending inheritance.”

Today, we know that “gemmules,” whatever they were thought to be, do not learn; it was a fabricated idea. And ironically, blending inheritance was soon recognized as an argument against Charles Darwin’s theory. Without a mechanism of inheritance, interest in Darwin’s theory by the end of the nineteenth century nearly vanished.

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