8.1: Scientific Contributions to a Theory of Evolution pg

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1 8.1: Scientific Contributions to a Theory of Evolution pg Key Terms: paleontology, catastrophism, uniformitarianism, inheritance of acquired characteristics, theory of evolution by natural selection, evolution, survival of the fittest, and descent with modifications. Where did we come from? has been debated for thousands of years. The first explanations of life were influenced by religion and philosophy, and all life forms have existed, unchanged since their creation s introduced empirical studies to explain the natural world, through observation and experimentation to form new ideas and hypotheses about nature. John Ray ( ) first used empirical studies to classify plants and animals based on anatomy and physiology. Carolus Linnaeus ( ) extended the classification system. Georges-Louis Leclerc, Comte de Buffon ( ) Was one of the first to challenge the idea that life forms are unchanging, explained in his 44 - volume Historie Naturelle. Buffon noted similarities and difference between humans and apes, and speculated that they may have a common ancestor, suggesting the species has changed over time. Buffoon also suggested that Earth was more then 6000 years old, as originally believed. His ideas led others to question whether life is unchanging.

2 The Science of Paleontology Fossils are important part to the study of evolution. Fossils are preserved remains of once-living organisms. Georges Cuvier ( ) studied fossils, and is accredited with developing the science of paleontology, the study of ancient life through the examination of fossils. Paleontology is the study of ancient life through the examination of fossils. Cuvier determined that in each stratum (layer of rock) is characterized by a unique group of fossil species, also the deeper (older) stratum, the more dissimilar the species are from the modern versions. Cuvier determined that new species appeared and others disappeared over time and species can become extinct. Figure 8.2: Deep rock strata are older than strata closer to the surface. Different species of fossilized organisms can be found in different sedimentary rock strata. This is evidence that not all life forms came into existence at the same time.

3 Catastrophism Cuvier explained his observations by proposing the idea that the Earth experienced many destructive natural events in the past, such as; floods, and volcanic eruptions. These events were violent enough to have killed numerous species each time they occurred, which he called revolutions. After these revolutions or catastrophes, the area would be repopulated by organisms from other nearby unaffected areas, explaining why fossils of species that did not exist any more was found in the stratum. Catastrophism is the idea that catastrophes such as floods, diseases, and droughts periodically destroyed species living in a particular region, allowing species from neighbouring regions to repopulate the area? Charles Lyell ( ) Lyell did not accept Cuvier s theory of catastrophism, but proposed his own theory of uniformitarianism. His theory was based on geologist s James Hutton s idea that geological processes are operating at the same rate as in the past. If geological processes are slow and continuous rather than catastrophic (building and eroding mountains), the Earth might be more than 6000 years old. Even though these changes occur over long periods of time, it still resulted in substantial changes. If Earth is slowly changing, could populations change also occur slowly? Uniformitarianism is Charles Lyell s theory (based on Hutton s theory) that geological processes operated at the same rates in the past as they do today. Learning Check: questions 1 6, pg. 327

4 Jean-Baptiste Lamarck ( ) Lamarck outlined his ideas about changes in species over time, by comparing current species of animals with fossil forms. He observed a line of decent or progression in which a series of fossils (from older to more recent) led to modern species. Lamarck believed the organisms would become better adapted to their environments. Any body parts used more often to survive would become larger and stronger, such as; the giraffe that developed longer necks and tongues to eat leaves higher up in the trees. He theorized that these developments would be passed on to their offspring, calling it Inheritance of acquired characteristics. Also the body parts not used would disappear or not be passed on. The importance to Lamarck s theory is the fact that the environment, and the organism s adaptation to the environment, resulted in characteristics that could be passed on to the next generation. Inheritance of acquired characteristics is the idea that characteristics acquired during an organism s lifetime can be passed on to its offspring. Charles Darwin ( ) In 1831, Darwin at age 22; sailed on the HMS Beagle with the primary purpose of surveying and mapping the coast of South America. During the voyage Darwin also had the opportunity to explore these new lands. His observations and ideas later became his theory of evolution.

5 His main five observations and questions were: Observation: 1. The flora and fauna of the different regions visited were distinct from those found in England and Europe. 2. Fossils of extinct animals looked very similar to living animals 3. Animals (finches) observed on the Galapagos Islands closely resembled animals he had observed on the west coast of South America. 4. Animals (finches) on the Galapagos Islands varied slightly from island to island. 5. Traits can be passed on from parent to offspring, and through sexual reproduction, variations within the species is occurs. Questions: 1. If all organisms originated in their present form in one singular event, why were there distinctive clusters of similar organisms in different regions of the world? Why were all types of organisms not randomly distributed? 2. Why would live and fossilized organisms that looked similar be found in the same region? 3. Why did the Galapagos species so closely resemble organisms on the adjacent South American coastline? 4. Why was there such diversity of species in such a small area? Could these species have been modified from an ancestral form that arrived on the Galapagos Islands shortly after the islands were formed? 5. Could a process similar to artificial selection also operate in nature?

6 Theory of evolution by natural selection is a theory explaining how life has changed, and continues to change, during Earth s history. Evolution is the process of genetic change in a population over time. Darwin, Wallace, and the Theory of Evolution by Natural Selection Alfred Russel Wallace ( ) was developing similar conclusions to Darwin s. Populations change over time, but the question is what was the mechanism for these changes. Thomas Malthus ( ) wrote an essay called an Essay on the Principles of Population, which introduced the key idea used by Darwin. Malthus suggested that populations produce far more offspring than their environment (food, shelter, and mates) can support. Starving and disease were factors to reductions in population. Darwin accepted Malthus premise and suggested that organisms with traits that helped them survive their environments were more likely pass on to their offspring. Darwin reasoned that through competition for limited resources between individuals of the same species would select for individuals with favourable traits, traits that increased their chances to survive and reproduce. As the population grows from generation to generation the proportion of the trait occurring in the population increases. This is the idea of Survival of the Fittest and Darwin called it natural selection. Darwin published his findings in 1859, The Origins of Species.

7 Darwin s theory of natural selection showed how populations of individual species became better adapted to their environments over time. Summary: 1. Organisms produce more offspring than can survive. Therefore, organisms compete for limited resources. 2. Individuals of a population vary extensively, and much of this variation is heritable. 3. Individuals that are better suited to local conditions survive to produce more offspring. 4. Processes for change are slow and gradual. Survival of the Fittest is the idea that the organisms that are the fittest leave the most offspring, so those organisms win the struggle for survival; phrase coined by John Spencer. Descent with Modification Darwin discussed the decent of modification instead of evolution in his book The Origins of Species. He believed the evolution meant progression or getting better, but natural selection does not demonstrate progress, and has no set direction. It is on based on individuals in the population that have the ability to survive the local environmental conditions and these traits are passed on. Decent with Modification - is Darwin s theory that natural selection does not demonstrate progress, but merely results from a species ability to survive local conditions at a specific time.

8 Review Questions: 1 15 pg. 331 Activity 8.1: Building a Theory pg. 330 Thought Lab 8 A: Comparing the Ideas of Lamarck and Darwin pg. 341 Study Guide: Self Assessment 1 14 SG Developing the Theory of Evolution by Natural Selection (8.1) 1 4, SG