Evolution: A History and Process

1. Evolution: A History and Process

2. Darwin Developed a theory of evolution:Ideas from Darwin’s Time • Evolution is all the changes that have transformed life over an immense time. • Before Darwin two ideas about life prevailed: • Organisms are fixed, they do not change • Earth was only 10,000 years old and relatively unchanged.

3. Darwin Developed a theory of evolution:Ideas from Darwin’s Time • In the mid-1170’s, the study of fossils led French naturalist Georges Buffon to suggest that the Earth might be much older than a few thousand years, • He also observed that specific fossils and certain living organisms were similar but not alike.

4. Darwin Developed a theory of evolution:Ideas from Darwin’s Time • In the Early 1800’s another French naturalist Jean Baptiste Lamarck proposed that life changes. • He recognized that species change and are not permanent. • Lamarck explained evolution as a process of adaptation. • Today we explain adaptation to be an inherited characteristic that improves an organisms ability to survive and reproduce in a particular environment

5. On a cold winter day in 1831, HMS Beagle set sail on a voyage around the world. The main mission of the voyage was to chart poorly known stretches of the SouthAmerican coast line. On the voyage was 22 year old college graduate Charles Darwin. His main interest was to study the geology, plants, and animals encountered on the voyage. The Voyage of the Beagle

6. Route of the Beagle

7. Darwin’s Observations • Darwin spent most of his time on shore while the ship’s crew surveyed. • There he observed and collected thousands of specimens from plants and animals. • He studied the organisms and their adaptations from places as different as the Brazilian Jungle to the frigid lands near Antarctica.

8. Darwin’s Observations • Throughout the voyage and for the rest of his life Darwin maintained extensive journals of his observations, studies, and thoughts. • Darwin became convinced after the voyage that species change as they adapt to their environment. • Darwin also notice that in South America some of the fossils he found were larger versions of what was living. This observation helped him suggest that organisms from today came from an ancestral species.

9. Darwin’s observations • Darwin was also intrigued by a group of islands called the Galapagos. • He observed that the island contained many unique species. Most of the of the species on the island were similar to the organisms on the mainland. He also noticed that these organisms differ from one island to another. • He concluded that the mainland species had changed after they colonized the islands and adapted to their various new environments.

10. Ideas from Geology • Charles Lyell also had a profound impact on Darwin. • Lyell proposed that gradual and observable geological processes such as erosion could explain physical features of today’s earth. • Darwin did experience an earthquake in which he saw land that was underwater before an earthquake above the water after the earthquake occurred.

11. Ideas from Geology • Darwin reasoned that earthquakes gradually lifted the rock baring marine fossils from the sea floor. • The geologic evidence presented by Lyell and others pointed to 2 conclusions • Slow processes of mountain building and erosion suggested an Earth must be old • These processes cause major change to the Earth • Darwin would eventually apply this idea of gradual change to the evolution of the Earth’s life forms.

12. Darwin Publishes His Theory • Once Darwin returned home from his voyage he continued to work on his theories. • In 1838, as Darwin continued to think about the question of how species change, he read an essay on human populations written a few decades earlier by Thomas Malthus. • Malthus contended that much of human suffering, such as disease, famine, and homelessness, was due to the human population's potential to grow. • That is, populations can grow much faster than the rate at which supplies of food and other resources can be produced.

13. Darwin Publishes His Theory • Darwin recognized that Malthus's ideas applied to all species. • The production of more individuals than the environment can support leads to a struggle for existence. • This concept helped Darwin to propose a mechanism of evolutionary change.

14. Darwin Publishes His Theory • In 1844, Darwin wrote a 200-page essay that outlined his idea, but he didn't release it to the public. Instead, for the next several years he continued to accumulate more evidence to support his idea. He told only a few of his closest colleagues, who encouraged him to publish his work before someone else came to the same conclusions. • In 1858, another British naturalist, Alfred Wallace, did come to the same conclusion. Darwin was shocked to receive a letter from Wallace that described the same basic mechanism for evolutionary change that Darwin had proposed. • Within a month, some of Wallace's and Darwin's writings were jointly presented in public. • Darwin published his book The Origin of Species about a year later.

16. Darwin’s 2 Main Points • First, he argued from evidence that the species of organisms living on Earth today descended from ancestral species. Darwin proposed that the descendants of the earliest organisms spread into various habitats over millions of years. In these habitats, they accumulated different modifications, or adaptations, to diverse ways of life. • Darwin called this process descent with modification. He saw descent with modification as a way to account for the diversity of life. • For example, the jackrabbit and the snowshoe hare are two species of hares that have adapted to living in different environments. The jackrabbit benefits from fur that blends well in the desert and ears, rich with blood vessels, that help cool its body. White fur provides protective camouflage in the snowy northern regions of the snowshoe hare's range.

17. Darwin’s 2 Points • Darwin's second main point was his argument for natural selection as the mechanism for evolution. • Natural selection is the process by which individuals with inherited characteristics well-suited to the environment leave more offspring on average than do other individuals.

18. This model demonstrates how certain inherited characteristics well-suited for the environment leave more offspring on average than others.

19. Darwin’s 2 Theories • When biologists speak of "Darwin's theory of evolution," they are referring to natural selection as a cause of evolution. The result of natural selection is adaptation. This process of natural selection is another way of defining evolution.

20. Darwin proposed natural selection as a mechanism of evolution • In biology, a population is a group of individuals of the same species living in the same area at the same time. • Suppose an animal species from a mainland colonizes a chain of distant and isolated islands. The individuals of that species on each island make up a separate population. Populations on the different islands would adapt to their local environments. Over time, the isolated populations would become more and more different. And over many generations, the populations could become different enough to be separate species.

21. Darwin proposed natural selection as a mechanism of evolution • The evolution of finches on the Galápagos Islands is an example. Darwin did not realize the significance of these finches until later, after he returned to England. Still, these finches are known as "Darwin's finches" for their contribution to the theory of natural selection.

22. Observations Lead to a Question • There are 13 species of finches unique to the Galápagos islands. However, they most closely resemble one finch species living on the South American mainland. • A reasonable hypothesis is that the islands were colonized by a single finch species that strayed from the mainland. This single species adapted to the habitats on the islands and eventually diversified into the 13 species. • A key characteristic of the finches is their beaks, which are adapted to specific foods available on the different islands. • A question that follows is, "How did these different beaks arise?" Darwin's theory proposes that these differences arose through natural selection.

23. More Observations Lead to an Idea • Darwin based his theory of natural selection on two key sets of observations. • First, drawing from Malthus's ideas about humans, Darwin recognized that all species tend to produce excessive numbers of offspring. But in nature, resources are limited. The production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population. In most cases, only a small percentage of offspring will survive in each generation.

24. More Observations Lead to an Idea • Darwin's second set of observations was his awareness of variation among the individuals of a population. Variation refers to differences among members of the same species. Much of this variation is heritable and passes from generation to generation. This explains why siblings usually share more traits with one another and with their parents than they do with unrelated members of the same population.

25. More Observations Lead to an Idea • From these two sets of observations Darwin developed his theory of natural selection. • Individuals with inherited traits that are best suited to the local environment are more likely to survive and reproduce than less fit individuals. • Darwin also reasoned that natural selection could eventually cause two isolated populations of the same species to become separate species as they adapted to their different environments. This would explain patterns such as those observed in the Galápagos finches.