The most important book ever: On The Origin of Species by Charles Darwin

 "Nothing in biology makes sense except in the light of evolution" - Theodosius Dobzhansky

I can't believe I let myself get to my fourth decade of life before reading this. This book is the foundation of all modern biology and all my professional knowledge as a doctor and a scientist, and it's available for free and in a readable style.

Darwin takes the limited knowledge of the 19th century and links it all together to build an unassailable conclusion. He begins by noting the powerful effects of selective breeding on crops and livestock. Humans spot small, natural differences in animals and breed them for that trait. Over the decades this creates new varieties. If small, natural differences in wild animals arise that affect their ability to survive and reproduce, nature could obviously select for new varieties too. He traces this argument through the fossil record and the tree of life. He shows how the distribution of species around the world only makes sense via a story of migration and speciation to fill ecological niches.

What's truly remarkable to me is that from these humble beginnings Darwin begins questions that biologists are still talking about today. He lays out a new view of heredity, parasitism, and insect sociology. He creates the concept of sexual selection and shows some of the strange consequences, such as the peacock's tail. He notes the similar bony structure of the wing of the bat, the fin of the whale, and the arm of the ape, building the first models of divergent evolution of homologous structures.

Always the gentlemen scientist, Darwin was modest and suitably self-skeptical. He therefore spent many years refining his theory before publishing. He notes difficulties with his theory that remained to be investigated, including gaps in the fossil record and complex structures and behaviours that are hard to break into intermediate steps. He models plausible paths for the gradual development of such irreducible structures as the wing and the eye.

“If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.”

Of most interest to me in my new study of the human mind, he notes that instinct and behaviour are selectable traits just as important as anatomical and physiological ones, and shows how complex behaviour such as ant enslavement and beehive construction hexagonal cells can arise gradually. I'm so grateful to Darwin for this beautiful theory, which may be the most important idea ever.

"...from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved"