Ongoing debates: the environment as the principle cause?

The second considers particular historical changes in the environment to be an important cause, but still acknowledges the role of chance. Fitness landscapes can help us visualise this option since they allow us to more easily see the shaping role of the environment. In this view natural selection acts merely to drive organisms up hill, but the actual ends of evolution are dictated (caused) by the contours of their environment. Natural selection performs a role analogous to the influence of gravity on objects moving on a physical landscape (albeit a bizarre form of gravity that drives things up hill instead of down). This is essentially Gould’s position. Pointing to the pivotal role of the ‘K - T’ asteroid impact that separated the Cretaceous and the Tertiary period and ushered in a dinosaur free world and allowed the rise of mammals and humans, he says that “in an entirely literal sense, we owe our existence, as large and reasoning mammals, to our lucky stars.” If we were to re-run the ‘tape of life’ there is no guarantee of a K - T impact, so the chances become “vanishingly small that anything like human intelligence would grace the replay.” This accords well with Gould and Eldredge’s theory of ‘punctuated equilibrium.’ An event like the K - T impact would significantly alter the fitness landscape and natural selection would subsequently drive adaptations toward fitness in the new landscape until they reached the top of a peak, i.e. an equilibrium point. While this view considers the environment to be an important causal factor in biological history, in the final analysis the cause of adaptations is still chance, i.e. a random sequence of random environments.

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