What Darwin Didn't Know: The Modern Science of Evolution

Missing from On the Origin of Species is any account of how traits pass from one generation to the next. Explore the work on genetic inheritance by Gregor Mendel, whose pioneering rules of heredity remained essentially unknown for 35 years. Follow up with 20th-century pioneers, including Thomas Hunt Morgan and Theodosius Dobzhansky, who established the "modern synthesis" of evolutionary biology.

The arrival of genetics in the early 20th century addressed what Darwin did not know about inheritance, but there was more to uncover: How do genes function, and where do variations come from? Trace the discovery of DNA as the carrier of genetic information and the realization that mutations and other structural changes in DNA are a source of the modifications that underlie natural selection.

Natural selection is not the only mechanism driving evolution. In this episode, discover how the movement of individuals leads to gene flow between populations. Travel to the Galapagos Islands and neighboring Cocos Island to see how finches evolved into multiple species in the Galapagos archipelago but stayed a distinct species on isolated Cocos. Consider the implications for human evolution.

Trace the importance of geology in Darwin's thinking and his many observations that make sense only in light of the theory of plate tectonics, which was not developed until the 1960s. Chart the breakup, movement, and reassembly of continental plates that dispersed related flora and fauna all over the planet. Also look at the Wallace Line in Indonesia, which separates Asian from Australian species.

Explore how population bottlenecks and the founder effect lead to random changes in the frequency of genes, an independent mechanism of evolution known as genetic drift. Darwin had an inkling of this process when he proposed that "spontaneous variations" play a role in evolution. But genetic drift has proved far more significant than he ever envisioned.

Darwin thought evolution was an imperceptibly slow process, but it can happen remarkably quickly. Review Peter and Rosemary Grant's famous studies of Galapagos finches, along with the work of other scientists on guppies in Trinidad, moths in England, and foxes in Siberia. These show evolution playing out in real-time as creatures adapt to changing conditions within a few generations.

One thing Darwin never anticipated was that evolution would be observed in the laboratory. In this episode, analyze lab experiments that shed light on the minute details of evolution, helping to settle a long-standing debate: Is the outcome of evolution random or predictable? Also cover digital life simulations, which inspire new ideas that can be tested with living populations.

Despite its title, On the Origin of Species does not fully address how new species arise. Delve into this complex problem by investigating what a species is. Consider definitions based on morphological, biological, phylogenetic, and genomic distinctions. Then examine the reproductive barriers, both before conception and after, that can lead to the origin of new species.

Darwin was puzzled by the sudden appearance of complex, diverse flora and fauna in the fossil record roughly 540 million years ago, a period known as the Cambrian explosion. And Darwin had no idea that the history of life on Earth has included five big mass extinction events followed by accelerated periods of evolution that often took life in radically new directions.