GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
Evolution II: On the Origin of Species by Means of Natural Selection

Jean-Baptiste Lamarck (French: late 1700s-early 1800s) produced predominant theory of evolution prior to Darwin. In fact, "Lamarckian" evolution (as used in most textbooks) is just the theory of inheritence from acquired characters, which wasn't original to him. In general, Lamarck and other early evolutionists believed in:

Flaws with Lamarckian Evolution:


Darwinian evolution differs from Larmarckian ideas in three main aspects:

[NOTE: Remember that "theory" doesn't mean "guess" or "hypothesis", but rather some model of broad explanatory power.]

Although we call the above set of theories "Darwinian Evolution", it was actually independantly discovered to by two different naturalists during the mid-1800s:

Their basic observations which led to the discovery of Natural Selection: Thus, IF some variation gives the individual a slight advantage (bigger, stronger, smaller, smarter, less tasty, whatever) at surviving; and IF that variation is inherited; THEN there is a somewhat better than average chance that organisms with that variation will survive to bear the next generation. Over the long expanse of geologic time, the accumulation of these variations will change the population from one form to another: the origin of species.

This process is analogous to artificial selection (i.e., domestication), and thus called natural selection.

NOTE: Natural Selection is NOT "survival of the fittest", as commonly thought. Or more accurately, "fitness" is NOT a measure of individual strength, speed, intelligence, or so forth, but rather is an index of reproductive success.

NOTE ALSO: Darwin did not use the word "evolution" very often; instead, preferred the phrase "descent with modification".

Darwin pointed out a subset of Natural Selection: Sexual Selection, where the variation is "being more sexy" (and thus have better than average chance of breeding, and thus passing on "sexiness", compared to other members of the population): peacock tails, bird song, etc.

Many similarities to Lamarckism: homology due to common ancestry, for example.

Primary difference: adaptations due to differential survival of variations in a population, not to accumulation of characters acquired in the lifetime of the organisms.

Evolution by natural selection explained a lot:

For those interested in some of the original literature on the subject, click here for the joint Darwin & Wallace paper of 1858 (actually, it was a series of short papers and letters published together) and here for the text of the first edition of The Origin of Species.

To Next Lecture.
To Previous Lecture.
To Syllabus.

Last modified: 14 July 2006