Darwin’s Theory of Evolution Chapter 15 Darwin’s Theory of Evolution

15-1 The Puzzle of Life’s Diversity Evolution: The process by which modern organisms have descended from ancient organisms. A gradual change in a species (populations) through adaptations over time We share the world will millions of other kinds of organisms (diversity). Related? Arise?

Scientific theory: a well-supported testable explanation of phenomena (events) that have occurred in the natural world. We call it a theory. Heliocentric theory by Copernicus.

Charles Darwin (1809 – 1882) Contributed greatly to evolution Contributed the most to evolution, born on same day as Abraham Lincoln, at the age on the left...

In 1831, Darwin set sail from England aboard the H. M. S In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world. It took 5 years. During his travels, Darwin made many observations and collected evidence that led him to propose a hypothesis about the way life changes over time. joined the crew of the ship Beagle and traveled the world for 5 years, visiting several continents and many remote islands.

Darwin’s Observations Many different species inhabit the earth. Plants and animals were well suited to the environments they inhabited (lived). Why certain species lived where they did. Fossils (preserved remains of an ancient organism): some looked similar to todays species and some looked completely different. During a single day in a Brazilian forest, he collected 68 different species (or types) of beetles - species: group of similar organisms that can breed and produce fertile offspring found they each had unique adaptations No rabbits in Australia? No similar species (or types) of animals in grasslands of Europe and Australia?

The Galapagos Islands Close together, but with very different climates Lowest – hot dry and barren Higher islands – greater rainfall and different assortments of plants and animals Isabella – rich vegetation (plants) Darwin observed that the characteristics (traits) of many animals (the shapes of Tortoises shells and Finches beaks) and plants varied noticeably among the different islands of the Galapagos.

15-2 Ideas That Shaped Darwin’s Thinking 1795 - Scientists Hutton and Lyell helped show: Earth is many millions of years old The processes that changed Earth in the past are the same that operate in the present

Wrong!! 1809 - French scientist Lamarck proposed Evolution hypothesis: By selective use (or disuse) of organs, organisms acquired (or lost) certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species. However, he paved the way for the work of later biologists. Wrong!! Lamarck didn’t know: - how traits are inherited. - that an organism’s behavior has no effect on its heritable characteristics. 1809 – year Darwin was born A male fiddler crab uses its front claw to ward off predators and to attract mates. Because the front claw is used repeatedly, it becomes larger. This characteristic (large claw) is passed onto its offspring. However, he paved the way for the work of later biologists.

Traits change over generations, not an individuals lifetime! Wrong!! Traits change over generations, not an individuals lifetime!

15-3 Darwin Presents His Case “Theory of Evolution by Natural Selection ” (1859) 1836 – Darwin returns, he discussed his work with friends but put away his writings (wife/died) 25 years later – essay by Alfred Wallace who had been studying similar changes in species 1859- on the origin of species

Evolution by Natural Selection Darwin proposed that new species could develop by a process of natural selection. Natural selection: tool for change in a population when better adapted organisms survive to produce a greater number of viable (practical) offspring has the effect of increasing their proportion (number) in the population so they become more common Just as we selectively breed animals for desired traits, nature weeds out those without the best traits There are 13 types of Galapagos finches, also known as Darwin's Finches, and they share the same habits and characteristics except for one: All 13 have different beaks. The differences in their beaks might be the most important aspect of their survival. Two documented examples of that survival occurred in the late 1970s and mid 1980s. First, when a large drought affected the island in 1977, seeds became scarce. Finches with the largest, toughest beaks were able to eat larger seeds that weren't typically part of their diet. As a result, they survived. Finches with smaller beaks were unable to crack the tough seeds and many died. Through the process of natural selection, the birds that were able to adapt reproduced and thrived, while the others dwindled in number. However, adaptation can go both ways, as was seen during rainy weather in 1984 and 1985. The heavy rains created more of the small, soft seeds and few of the large ones. This time, more birds with the smaller beaks survived and produced more offspring.

Evidence of Evolution Geographic Distribution of Living Species The Fossil Record Geographic Distribution of Living Species Similarities in Embryology Anatomical Structures

The Fossil Record Provide a record of early life and evolutionary history. By comparing fossils from older rock layers with fossils from younger layers, scientists document the change in life on Earth over time.

Evolution of the Beluga Whale

What can we learn from fossils?

Geographic Distribution of Living Species Galapagos finches could have descended with modification (changes) from a common ancestor

Similarities in Embryology The early stages, or embryos, of many animals with backbones are very similar. The similarities suggest evolution from a distant, common ancestor.

Anatomical Structures Homologous structures : Structural features with a common evolutionary origin that are similar in arrangement and/or function.

Analogous structures : The body parts of organisms that do not have common evolutionary origins but are similar in function.

Vestigial structures : do not have current function but may have been useful to an ancestor

Summary of Darwin’s Theory Organisms differ, and some of this variation is heritable (passed from parent to offspring). They produce more offspring than can survive off of limited resources. Each has unique advantages and disadvantages in the struggle for existence.

Summary, Continued Individuals best suited to their environment survive and reproduce most successfully, passing their heritable traits to their offspring. Other individuals die or leave fewer offspring. This way, species change over time through natural selection. Species alive today are descended with modifications from ancestral species that lived in the distant past. Finish giraffe example

Vocab Evolution Theory Fossil Natural selection