Charles Darwin’s Theory of Evolution

Introduction Charles Darwin was a biologist who lived during the 1800s – Scientific thinking was shifting (biology & geology) Evolution = the process of change over time Darwin developed a theory that explains how modern organisms evolved over long periods of time through descent from common ancestors.

Darwin’s Observations Darwin was invited to sail aboard the HMS Beagle’s 5-year journey – The captain and crew were mapping the coastline of South America – Darwin was collecting animal and plant specimens and making notes about the biological diversity (species) he observed – They visited South America, remote islands, New Zealand, Australia, and the southern tip of Africa

Examples Birds: – Rheas are similar to ostriches but live on separate continents – Finches on the Galapagos Islands were similar but each species had a differently-shaped beak Marsupials are found only on Australia Fossils – Many fossils that Darwin collected resembled living species.

Other Scientists’ Ideas James Hutton and Charles Lyell (Geologists) – Concluded that the Earth is extremely old – The processes that changed Earth in the past were still operating in the present. Jean-Baptiste Lamarck (Biologist) – Suggested that organisms could change by using or not using parts of their bodies Thomas Malthus (Economist) – Studied factors that limited population growth

Artificial Selection Plants and animals are bred for certain characteristics – Cows that produce more milk – Horses that run faster – Plants that produce better fruit – Dogs that possess certain skills (dog breeds) Artificial selection = nature provides the variations in a species, but humans select those that they find useful. (Darwin had NO idea how heredity worked)

Darwin’s Conclusions Organisms struggle to survive – They compete for limited resources Some variations are more beneficial than others (adaptations) – Individuals with these variations were more likely to reproduce and pass them on to offspring. “Survival of the fittest” – An organism’s fitness describes how well it is able to survive and reproduce in its environment

Natural Selection The process by which organisms with certain variations are more likely to survive and produce more offspring. – The natural environment determines fitness Natural selection exists when organisms compete for resources, possess variations, and there are different levels of fitness among individuals in a population.

Evidence for Evolution 1. Biogeography – Patterns of species distribution – Closely related but different = variations among populations that resulted in the development of different species – Distantly related but similar = species that are similar and live in similar environments but in different locations 2. Fossils – The geologic record of organisms that have lived in the past – Some extinct organisms are similar to living species.

3. Anatomy and Embryology – Homologous structures = structures that are anatomically similar but have different uses Ex: arm bones of amphibians, reptiles, bird wings, and mammals – Vestigial structures = traces of structures Ex: hip bones in marine mammals, tailbones – Embryos of different species show similar development patterns 4. Genetics and Molecular Biology – All organisms share the same basic genetic code