15-1 The puzzle of life’s diversity How did different organisms arise? How are they related?

Evolution: change over time Describes the process by which modern organisms descended from ancient ancestors. A scientific theory is a testable explanation for what we see in nature. Charles Darwin proposed this revolutionary idea in 1859. Galapagos hawk and land tortoise

Voyage of the HMS Beagle 1831: sets sail for a voyage around the world to map harbors for the English crown. Charles Darwin, a 21 yr old college graduate, serves as ships’ naturalist (unpaid) Observations and evidence he collected on this voyage later became the theory of evolution.

The voyage of the HMS Beagle: 3 years to circumnavigate the globe

Overland collecting Darwin was seasick, so he traveled overland whenever he could. He collected fossils, plants and animals everywhere he went. He kept journals of his findings, seeing each specimen as a piece of a puzzle: How can science explain the diversity of life on earth? Whale fossil, Chile Marine fossils, Patagonia

Patterns of diversity Hippopotamus, Africa Capybara, S America Adaptation: plants and animals are well suited for the different environments they inhabit. Diversity: animals and plants vary widely in similar habitats. Distribution: some species have a wide range, others only live in one place.

Living organisms and fossils Giant ground sloth fossil, S America Sloths today Fossils: remains of extinct animals Darwin collected fossils from deposits in S. America Why had so many species disappeared? How are fossils related to living species?

Galapagos A small group of islands 800 miles from Ecuador. Low islands are desert-like, higher ones have more rainfall, and a greater assortment of plants and animals. Land tortoises are different on every island: the shape of their shells could be used to tell what island they came from. Darwin also studied the marine iguanas, which live nowhere else in the world but in the Galapagos islands.

Collections Darwin collected birds from each island, noting their beak shape. He thought they were wrens or warblers. His man servant collected plant samples from each island, one press per island

The journey home Darwin tried to make sense of what he’d seen in the Galapagos. He thought about how much the plants and animals varied on each island. Galapagos land and marine iguanas

Change over time He hypothesized that the separate species could have come from a single ancestor species arriving on a raft of vegetation from South America . Darwin’s answers to these questions would turn the world of biology upside down.

Review questions 1. What did Darwin collect as ship’s naturalist? 2. Why did Darwin spend so much time on land if he was on an ocean voyage? 3. What was unusual about the Galapagos tortoises? 4. What was the most interesting thing you learned in this lecture?