Warren Walker, emeritus professor of biology, Oberlin College

To the editor:On Feb. 12, biologists and many others will celebrate the 200th anniversary of the birth of Charles Darwin, and in November we commemorate the publication 150 years ago of his seminal book, "On The Origin of Species by Means of Natural Selection." Although evolutionary ideas had been proposed many years before the publication the "Origin," Darwin drew together a large and convincing body of evidence for "descent with modification" from comparative anatomy, embryology, paleontology, and plant and animal breeding. Chromosomes and genes were unknown to Darwin, but it was clear that plant and animal breeds and species varied, and that much of this variation was somehow inherited. This lead him to postulate the mechanism for evolution that natural selection working on this variation would lead to the "preservation of the favored races in the struggle for survival".His ideas were at first very controversial, but over the years the discovery of chromosomes and genes, DNA (deoxyribonucleic acid), and recent work in experimental embryology, microbiology, biochemistry and the sequencing of the genome in many different species have reconfirmed his views time and time again. Yet there is much more to learn about the details of the mechanism of evolution.Evolution and natural selection have become the basic integrating concepts of biology and medicine underlying and bringing together their diverse fields. Nearly all organisms share the same basic cellular chemistry and components and method of inheritance. Evolution is to biology what the work of Galileo is to astronomy, and the concepts of continental drift and plate tectonics is to geology. The universe and earth evolve, stars are born and die, mountains rise and fall, and species arise and become extinct. Change is universal, but all is governed by principles that are gradually becoming understood.