The Making of a Theory: Darwin, Wallace, and Natural Selection — HHMI BioInteractive Video

Key Concepts:

• Special Creation: The belief that each species was individually created by God in its present form and is unchangeable.
• Natural Selection: The process by which species change over time due to variations that give individuals a survival and reproductive advantage.
• Species Variation: The small differences that exist among individuals within a given species.
• Tree of Life: The concept that all species are connected to one another in a family tree, with species arising from other species.
• Wallace Line: A boundary that splits the Malay Archipelago, with animals on the eastern islands resembling those of Australia and animals to the west resembling those of Asia.
• Vestigial Structures: Imperfections or apparently useless structures in organisms that suggest they are modified forms of older species.

Darwin's Voyage on the Beagle:

• Initial Beliefs: Charles Darwin initially believed in special creation and planned to become a clergyman.
• Opportunity: Darwin joined the Beagle voyage as a companion for the captain and to study natural history.
• Experiences: Darwin experienced seasickness and collected animals, plants, and rocks around the globe.
• Fossil Discoveries: In Argentina, Darwin found fossils of extinct creatures like glyptodon and ground sloths, which were much larger than living species.
• Galapagos Islands: Darwin visited the Galapagos Islands, where he observed distinct species of tortoises and mockingbirds on different islands.
• Tortoises: Spaniards told Darwin that they could tell which island a tortoise came from just from the shape of its shell.
• Mockingbirds: Darwin noticed that each kind of mockingbird lived on a different island.
• Radical Idea: The Galapagos animals led Darwin to consider that species might change over time.

Darwin's Theory of Evolution:

• Mental Rioting: After returning to England, Darwin engaged in "mental rioting," letting his thoughts stream to him.
• Species Change: Darwin concluded that species change into new species over time.
• Family Tree: Darwin proposed that all species are connected to one another in a family tree.
• Heresy: Darwin's ideas were considered heresy because they contradicted special creation and church teachings.
• Secrecy: Darwin kept his ideas secret for many years due to fear of attack and ruin.

Wallace's Journey and Discoveries:

• Amazon Expedition: Alfred Russel Wallace spent four years collecting animals in the Amazon jungle, but his specimens were destroyed in a shipwreck.
• Malay Archipelago: Wallace traveled to the Malay Archipelago to collect and study animals.
• Butterflies: Wallace was captivated by butterflies, especially birdwings, and identified new species.
• Species Change: The Malay butterflies suggested to Wallace that species change.
• Geographical Distribution: Wallace compared the geographical distribution of animals and formulated a new law of nature: new species arise near similar species.
• Tree of Life: Wallace independently arrived at the concept of the tree of life.
• Vestigial Structures: Wallace recognized that vestigial structures, such as finger bones in manatee flippers, indicate that species are modified forms of older species.
• Wallace Line: Wallace observed a distinct boundary in the Malay Archipelago, with different groups of mammals on either side.
• Island Connections: Wallace surmised that the eastern islands were once connected to Australia, while the western islands were connected to Asia.
• Natural Processes: Wallace understood that natural processes, such as volcanism and erosion, could change the shape of islands and continents.
• Variation and Death: Wallace realized that variation within species, combined with massive death, could lead to species change.
• Natural Selection: Wallace independently conceived the idea of natural selection.

Collaboration and Publication:

• Wallace's Letter: Wallace sent a letter to Darwin outlining his ideas on natural selection.
• Darwin's Shock: Darwin was shocked to receive Wallace's letter, as it summarized his own theory.
• Joint Presentation: Darwin's colleagues arranged for Wallace's manuscript and excerpts from Darwin's work to be read aloud together in London.
• Darwin's Publication: Darwin published his book, On the Origin of Species, in 1859, which became a sensation.
• Wallace's Book: Wallace eventually wrote a book on evolution, titled Darwinism.
• Friendship: Darwin and Wallace became lifelong friends.

Synthesis/Conclusion:

The video details the parallel journeys of Charles Darwin and Alfred Russel Wallace in discovering the theory of evolution by natural selection. Darwin's voyage on the Beagle provided him with crucial observations, particularly in the Galapagos Islands, that led him to question the prevailing belief in special creation. Wallace, independently exploring the Malay Archipelago, also arrived at similar conclusions about species change and natural selection. Despite the potential for competition, Darwin and Wallace ultimately shared credit for their groundbreaking work and maintained a lifelong friendship, revolutionizing the field of biology. The key takeaway is that both scientists, through meticulous observation, data collection, and theoretical reasoning, independently arrived at a revolutionary understanding of the origin and diversification of life on Earth.