Ch. 15 Darwin’s Theory of Evolution Ch. 15 Outline 15-1: The Puzzle of Life’s Diversity – The Voyage of the Beagle – Darwin’s Observations – The Journey Home Ch. 15 Outline 15-2: Ideas that Shaped Darwin’s Thinking – An Ancient, Changing Earth – Lamarck’s Evolution Hypotheses – Population Growth 15-3: Darwin Presents His Case – – – – – – Publication of On the Origin of Species Inherited Variation and Artificial Selection Evolution by Natural Selection Evidence of Evolution Summary of Darwin’s Theory Strengths and Weaknesses of Evolutionary Theory The Puzzle of Life’s Diversity Evolution: The process by which species change over time Theory: Well-supported testable explanation. It explains a phenomena. Voyage of the Beagle Charles Darwin – From England – Joined the crew of the H.M.S. Beagle as the ship’s naturalist – 5 year trip around the world – Darwin collected specimens at each stop Voyage of the Beagle Voyage of the Beagle Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. – This hypothesis is now called the theory of evolution. Darwin’s Observation Patterns of diversity – Many plants and animals seemed well suited to their environment – Organisms survived and reproduced in many different ways – Not all organisms lived everywhere Darwin’s Observation Living Organisms and Fossils Darwin collected fossils – Fossil: Preserved Remains of ancient organisms Some fossils didn’t resemble any living organisms Darwin’s Observations The Galapagos Islands – Off the west coast of South America – The Location that most influenced Darwin – Each Island had a different climate and different organisms – Noticed the birds had different shaped beaks on each island and tortoises had different shaped shells Darwin’s Finches The Journey Home After returning back to England, Darwin wondered if the birds he collected all belonged to the same species at some time An Ancient, Changing Earth James Hutton and Charles Lyell – Developed the theory that the earth is very old. This idea was contrary to what people thought at the time. Hutton and Geological Change: – Hutton was a geologist. He proposed that layers of rock form very slowly and others are pushed up from the sea floor to form mountains. (This takes a long time) Lyell’s Principles of Geology Lyell believed that the same processes that changed the Earth in the past still operate in the present. Darwin was influenced by Hutton and Lyell’s work. He reasoned, if the Earth can change over time (earthquakes, volcanoes) maybe life can change too! Lamarck’s Evolution Hypotheses Before Darwin’s work, Jean-Baptiste Lamarck observed that life changes and the species descend from other species. Lamarck’s Evolution Hypotheses Lamarck had two ideas: 1. Organisms can alter their bodies by “use and disuse” Use: Use a structure and it will change Disuse: Structures not used will disappear 2. Acquired characteristics can be inherited. If you increase your muscle mass your children will inherit your big muscles Lamarck’s Evolution Hypotheses Although Lamarck’s ideas were incorrect, he was one of the first ones to realize that organisms are adapted to their environments and propose a theory of evolution. Use and Disuse Population Growth Another influence of Darwin was Thomas Malthus. This scientist published a book in which he stated that babies were being born faster than people were dying. – Sooner or later food and living space will run out. Population Growth Darwin thought this applied to plants and other animals even more because humans usually only have one offspring at a time. – So why wasn’t the Earth completely covered in maple trees (for example)? Why were some surviving and others not? Darwin Presents His Case After Darwin returned to England in 1836, he continued to study his specimens. He discovered that the birds from the Galapagos were all finches, not wrens, warblers and blackbirds like he thought (found nowhere else in the world). The same was true for the tortoises – All the species resembled ones on the South America mainland, but they were a different species. Darwin Presents his Case Over 20 years later, Darwin published all his findings in a book called, On the Origin of Species. He didn’t publish it earlier because it went against the common beliefs about organisms. Not only did Darwin propose the theory of evolution, he also proposed a mechanism by which it happens: – Natural Selection Evolution by Natural Selection Darwin realized the organisms competed for resources (struggle for existence). He noted that organisms better suited to their environment (ex. Run faster, hide from predators) survived to reproduce and pass on their genes. Evolution by Natural Selection Fitness: The ability of an animal to survive and reproduce Adaptation: an inherited characteristic that increases an organism’s chance of survival Evolution by Natural Selection Successful adaptations, Darwin concluded, enable organisms to survive and reproduce. – Types of adaptations Structures Physiological processes Behavior Evolution of Natural Selection Survival of the fittest: individuals that are better suited for their environment survive and reproduce most successfully. (Natural Selection) Over time, natural selection results in changes in the inherited characteristics of a population. These changes increases a species’ fitness in its environment. Evolution of Natural Selection Darwin proposed that over long periods of time, natural selection produces organisms that have different structures. Species today look different than their ancestors Descent with Modification: Each living species has descended, with changes from other species over time. Evidence of Evolution Fossil Record Geographic Distribution of Living Species Homologous Body Structures Embryology Evidence of Evolution Fossil record-More Coming in Ch. 16 Geographic Distribution of Living Species – Similar organisms found in different places on Earth – Ex: Darwin’s Finches – Organisms under the same “pressures” had similar adaptations Homologous Body Structures Structures that have different mature forms but develop from the same embryonic tissues – Ex. Wings and arms – Help Scientist determine common ancestors – Not all homologous structures serve important functions Vestigial Organs: Organs reduced in size (Traces of homologous organs in other species) – Have little or no function Homologous Structures Turtle Alligator Ancient lobe-finned fish Bird Mammal Embryology Organisms that have similar developmental stages as embryos are more closely related to each other. Summary of Darwin’s Theory 1. 2. 3. 4. Individual organisms differ, and some of this variation is inheritable Organisms produced more offspring that can survive and there is competition for limited resources Individuals best suited survive and reproduce. Others die or leave fewer offspring. This process of natural selection causes species to change over time. Species alive today are descended with modifications.