Largest-scale Trends in Evolution - History of The Idea of Evolutionary Progress

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):

The inhabitants of each successive period in the world's history have beaten their predecessors in the race for life, and are, insofar, higher in the scale of nature; and this may account for that vague yet ill-defined sentiment, felt by many palaeontologists, that organisation on the whole has progressed.

As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world. Hence we may look with some confidence to a secure future of equally inappreciable length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.

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.

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". This may be compared to Gould's suggestion of "replacing the idea of progress with an operational notion of directionality".

Dawkins, on the other hand, proposes that Darwinian evolution is fundamentally progressive if progress is simply defined as "an increase, not in complexity, intelligence or some other anthropocentric value, but in the accumulating number of features contributing towards whatever adaptation the lineage in question exemplifies."

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, and trends in opposite directions also occur (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?