Lamarck’s Theory

In the eighteenth century the French naturalist Jean Baptiste de Lamarck believed that an animal’s use or disuse of an organ affected that organ’s development in the animal’s offspring. Lamarck claimed that the giraffe’s long neck, for example, resulted from its ancestors stretching to reach distant leaves. But because biologists could find characteristics never occurs. Yet new research has uncovered numerous examples of the phenomenon.

In bacteria, for instance, enzymes synthesize and break down rigid cell walls as necessary to accommodate the bacteria’s growth. But if an experimenter completely removes the cell wall from a bacterium, the process of wall synthesis and breakdown is disrupted, and the bacterium continues to grow—and multiply indefinitely—without walls. This inherited absence interactions among genes, without any attendant changes in the genes themselves.

A fundamentally different kind of environmentally induced heritable characteristic occurs when specific genes are added to or eliminated from an organism. For example, a certain virus introduces a gene into fruit flies that causes the flies to be vulnerable to carbon dioxide poisoning, and fruit flies infected with the virus will pass an ability that normally would have taken eons to develop through random mutation and natural selection.

The new evidence suggests that genes can be divided into two groups. Most are inherited “vertically,” from ancestors. Some however, seem to have been acquired “horizontally,” from viruses, plasmids, bacteria, or other environmental agents. The evidence even appears to show that genes can be transmitted horizontally between organisms that are considered to has long eluded biologists, and that may eventually prove Lamarck’s hypothesis to be correct.