Evolutionary synthesis: Dramatic change in our worldview

It is rather strange to contemplate the fact that we have just celebrated the 150th anniversary of the first publication of Darwin's On the Origin of Species (Darwin, 1859) and the 200th jubilee of Darwin himself. Considering the profound and indelible effect that Origin had on all of science, philosophy, and human thinking in general, 150 years feels like a very short time.

What was so dramatic and important about the change in our worldview that Darwin prompted? Darwin did not discover evolution (as sometimes claimed overtly but much more often implied, especially in popular accounts and public debates). Many scholars before him, including luminaries of their day, believed that organisms changed over time in a nonrandom manner. Even apart from the great (somewhat legendary) Greek philosophers Empedokles, Parmenides, and Heraclites, and their Indian contemporaries who discussed eerily prescient ideas (even if, oddly for us, combined with mythology) on the processes of change in nature, Darwin had many predecessors in the eighteenth and early nineteenth centuries. In later editions of Origin, Darwin acknowledged their contributions with characteristic candor and generosity. Darwin's own grandfather, Erasmus, and the famous French botanist and zoologist Jean-Bapteste Lamarck (Lamarck, 1809) discussed evolution in lengthy tomes.Lamarck even had a coherent concept of the mechanisms that, in his view, perpetuated these changes. Moreover, Darwin's famed hero, teacher, and friend, the great geologist Sir Charles Lyell, wrote about the "struggle for existence" in which the more fecund will always win. And, of course, it is well known that Darwin's younger contemporary, Alfred Russel Wallace, simultaneously proposed essentially the same concept of evolution and its mechanisms.

However,
the achievement of all these early evolutionists notwithstanding, it was Darwin who laid the foundation of modern biology and forever changed the scientific outlook of the world in Origin. What made Darwin's work unique and decisive? Looking back at his feat from our 150-year distance, three breakthrough generalizations seem to stand out:

1. Darwin presented his vision of evolution within a completely naturalist and rationalist framework, without invoking any teleological forces or drives for perfection (or an outright creator) that theorists of his day commonly considered.
2. Darwin proposed a specific, straightforward, and readily understandable mechanism of evolution that is interplay between heritable variation and natural selection, collectively described as the survival of the fittest.
3. Darwin boldly extended the notion of evolution to the entire history of life, which he believed could be adequately represented as a grand tree (the famous single illustration of Origin), and even postulated that all existing life forms shared a single common ancestor.

Darwin's general, powerful concept stood in stark contrast to the evolutionary ideas of his predecessors, particularly Lamarck and Lyell, who contemplated mostly, if not exclusively, evolutionary change within species. Darwin's fourth great achievement was not purely scientific, but rather presentational. Largely because of a well-justified feeling of urgency caused by competition with Wallace, Darwin presented his concept in a brief and readable (even for prepared lay readers), although meticulous and carefully argued, volume. Thanks to these breakthroughs, Darwin succeeded in changing the face of science rather than just publishing another book. Immediately after Origin was published, most biologists and even the general educated public recognized it as a credible naturalist account of how the observed diversity of life could have come about, and this was a dynamic foundation to build upon.

Considering Darwin's work in a higher plane of abstraction that is central to this book, it is worth emphasizing that Darwin seems to have been the first to establish the crucial interaction between chance and order (necessity) in evolution. Under Darwin's concept, variation is (nearly) completely random, whereas selection introduces order and creates complexity. In this respect, Darwin is diametrically opposed to Lamarck, whose worldview essentially banished chance. We return to this key conflict of worldviews throughout the book.