|
Three billion years ago, life on Earth consisted of single-celled organisms, but now there is a tremendous variety of complex multi-celled creatures. It may seem obvious that there is progress in evolution, but the topic has inspired much controversy. Ruse (1997) argues that many evolutionary theorists have implicitly or explicitly supported the notion of progress in evolution. Gould (1997) argues that there is no progress in evolution.
History of the idea of evolutionary progress Prominent historical figures who have championed some form of evolutionary progress include Alfred Russel Wallace, Herbert Spencer, Pierre Teilhard de Chardin, and Henri Bergson. Even Charles Darwin seems to have believed in some form of progress (Darwin, 1859):
Ruse (1997) presents a detailed and carefully researched survey of the idea of progress in evolutionary biology. He argues that belief in evolutionary progress is still prevalent among evolutionary biologists today, although it is often denied or veiled. Ruse (1997) writes, "A major conclusion of this study is that some of the most significant of today's evolutionists are progressionists, and that because of this we find (absolute) progressionism alive and well in their work." He claims that progressionism has harmed the status of evolutionary biology as a mature, professional science. Reformulating the question In examining the issue of evolutionary progress, the first step is to define progress. Ayala (1988) defines progress as "systematic change in a feature belonging to all the members of a sequence in such a way that posterior members of the sequence exhibit an improvement of that feature." He argues that there are two elements in this definition, directional change and improvement according to some standard. Whether a directional change constitutes an improvement is not a scientific question; therefore Ayala suggests that science should focus on the question of whether there is directional change, without regard to whether the change is improvement. Evolutionary theorists agree that there are local trends in evolution, such as increasing brain size in hominids, but these directional changes do not persist indefinitely (Gould, 1997). Evolution causes organisms to adapt to their local environment; when the environment changes, the direction of the trend may change. The question of whether there is evolutionary progress is better formulated as the question of whether there are any largest-scale trends in evolution (McShea, 1998). That is, is there a consistent directional change throughout the history of life on Earth? See also | ||||||||
|
| |||||||||
 |
|
| |