ENHS Nature Trails October 99 Article 2

Natural History and You - The President's Forum
by Nathan Tublitz

Evolution comes full circle: The resurrection of Lamarck

Evolution, as taught in high school biology classes, generally begins and ends with Darwin's theory of natural selection. Darwin postulated that better adapted organisms are more likely to survive and reproduce, thereby increasing their proportion in the population over time. Darwin's natural selection theory, attacked repeatedly since first presented in 1859, has stood the test of time for over 100 years and remains the only well-accepted mechanism of evolution (except in modern day Kansas).

Interestingly, Darwin's theory was initially not widely accepted because it conflicted with the accepted view about evolution at that time. In 1809 the French naturalist Jean Baptiste de Lamarck proposed that organisms could pass on traits acquired during their lifetime to their offspring. His classic example was the long neck of the giraffe. Lamarck suggested that the ancestral giraffe reached for food from higher and branches and in so doing, stretched and elongated its neck. This longer neck was inherited by the giraffe's offspring who proceeded to stretch their necks even further. This process continued across subsequent generations, supposedly resulting in the modern long necked giraffe.

Although there was considerable support for Lamarck's theory from his colleagues, there was precious little hard data in its favor and much anecdotal information against it. For example, any farmer could tell you that cutting the tail off a sheep did not mean that the sheep's offspring would have a smaller tail.

After Darwin's published his ideas on natural selection, Lamarck's theory soon dropped from favor and was seriously discredited when the actual basis of heredity was discovered and analyzed. That work showed that genetic information was transferred from parent to child through genes found in eggs and sperm. Differences in the traits of offspring could be explained by random alterations in the DNA of sperm or eggs, which caused the offspring to be better or less well adapted. This mechanism fit nicely with Darwin's theory of natural selection and allowed it to be tested and confirmed in many subsequent experiments. As Darwin's ideas soared, Lamarck's theory fell off the radar screens of most evolutionary biologists, primarily because of a lack of direct evidence.

Yet like so many good ideas that get shoved into the bottom drawer of the intellectual desk, Lamarck's theory has been recently brought back to the desk top by several intriguing and unexpected experimental results. In 1988, John Cairns starved bacteria and found that they mutated in a non-random way. These adaptive mutations not only allowed the bacteria to survive, they were passed on to the offspring of the survivors. This result provoked much controversy among biologists since it seemed to support Lamarck's much maligned ideas about evolution.

Cairns' results have been subsequently confirmed and extended by other researchers studying other organisms. A recent study of water fleas (Daphnia) shows that the size and shape of their head capsules or "helmets" vary according to the experience of the parents. If the parents are exposed to a specific chemical substance secreted by a predator, they grow longer helmets. So do their offspring, even if the offspring themselves were never exposed to the chemical. The same scientists have also showed that radish plants attacked by caterpillar predators respond in several ways, all of which are passed on to subsequent generations.

The demonstration that both plants and animals can transmit newly acquired defensive traits to their offspring hints that this phenomena might be widespread. Many biologists are now keen to find out if other environmentally-induced effects are similarly transmitted from parent to offspring and to identify the genetic mechanism responsible for these inter-generational effects. For example, the plague locusts of Africa exhibit striking behavioral and physiological changes when forming large swarms. Swarms often last for several generations and the changes observed in the initial swarming phase appear to be passed on to all subsequent offspring. Understanding how these and other environmentally induced changes carried across generations may be the first step in developing a new twist on the theory about evolution, one that forces a revisiting of Lamarck's intriguing ideas.

Nathan Tublitz
Professor of Biology
Institute of Neuroscience
University of Oregon
Eugene OR 97403
Phone: 1-541-346-4510 FAX: 1-541-346-4548

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