Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [36]
One may perceive that the bird of the shore, which does not at all like to swim, and which however, needs to draw near to the water to find its prey, will be continually exposed to sinking in the mud. Wishing to avoid immersing its body in the liquid, it acquires the habit of stretching and elongating its legs. The result of this for the generations of these birds that continue to live in this manner is that the individuals will find themselves elevated as on stilts, on long naked legs.
“Wishing” is only a crude translation of what Lamarck had in mind. He pictured a “subtle fluid” coursing through birds and all other living things, animating them and controlling their growth and movements. This subtle fluid was influenced by the habits the animals acquired as they explored the world. As a giraffe stretched for a leaf on a tree, the subtle fluid coursed into its neck. As more and more fluid traveled through it, the neck grew longer. Likewise, a wading bird stretched its legs to extract itself from the mud. It grew longer legs. Giraffes and wading birds alike could pass their altered bodies to their offspring.
Lamarck did not believe he was terribly original on this point. “The law of nature by which new individuals receive all that has been acquired in organization during the lifetime of their parents is so true, so striking, so much attested by the facts, that there is no observer who has been unable to convince himself of its reality,” he wrote.
And yet as common as that perception may have been, today Lamarck alone is linked to it. That’s because he described this change more provocatively than anyone else before him, making it part of an ambitious theory to explain the evolution of all of life’s diversity. Life, Lamarck argued, was forced to change by an inherent drive from simplicity to complexity. That drive has turned microbes into animals and plants. And at each stage of the rise of complexity, species have also acquired traits they need for their particular environment and have passed them down to their offspring.
Lamarck died in 1829, poor, blind, and scorned for his theory. But he raised questions that naturalists could not shake off: how to explain the fossil record, for example, and the distribution of similar species around the world. Thirty years after Lamarck’s death, Charles Darwin offered his own explanation. He argued for evolution, but he dismissed Lamarck’s inexorable drive from simplicity to complexity. Darwin instead argued that life evolved primarily by natural selection.
Each generation of a species contains a vast range of variations. In the case of shorebirds, some individuals have long legs and some have short ones. Some of those variations allow individuals to survive and reproduce more successfully than others. They pass down their traits to their offspring, and generation after generation their traits become more and more common. Over millions of years, natural selection can produce a wide range of bodies. In birds, for example, feet might evolve into the striking talons of eagles, the webbed flippers of ducks, and the slender poles that keep sandpipers from sinking into the mud. Natural selection acts only on the legs the birds are born with, not on any changes the birds might experience during their life.
By the late 1800s most biologists recognized the reality of evolution, but they were divided as to how life evolves. Many accepted natural selection, but others preferred something along the lines of Lamarck. The German biologist August Weismann wanted Lamarck banished from biology. He made his case by rearing mice and cutting off their tails along the way. Over many generations, the mice never grew shorter tails as a result. Neo-Lamarckians dismissed Weismann’s experiments as meaningless. The animals had not needed shorter tails, they argued, so they never produced them. The neo-Lamarckians doubted the power of natural