Mechanisms of Evolution

The Voyage of the H.M.S. Beagle In 1831, Charles Darwin set sail from England aboard the H.M.S. Beagle on a voyage around the world. Darwin collected numerous plant and animal specimens for his collection. He studied the specimens, read the latest scientific publications, and recorded his observations/thoughts in notebooks.

Darwin and the Galapagos Islands Darwin observed that the Galápagos Islands were in close proximity, but had very different climates and corresponding differences in vegetation. Accordingly, he observed that the characteristics of many animals and plants varied noticeably among the different islands.

Darwin’s Contribution to Science Darwin’s evidence led him to propose a revolutionary hypothesis pertaining to the way life changes over time. This hypothesis has become the theory of evolution. It was presented in his book, On the Origin of Species, published in 1859.

Darwin’s Case: Key Idea #1 Variation Within Species Members within a species vary from one another in important ways. At the time, variations were thought to be unimportant, minor defects. Darwin argued that this variation is significant.

Darwin’s Case: Key Idea #1 Variation Within Species

Darwin’s Case: Key Idea #2 The Struggle For Existence Darwin realized that high birth rates and a shortage of life's basic resources (food, water, and shelter) inevitably force organisms to compete for resources. Competition, both within and among species exists in almost all natural environments. This struggle is ultimately reflected by reproductive success

Darwin’s Case: Key Idea #2 The Struggle For Existence

Darwin’s Case: Key Idea #3 The Inheritance of Traits Characteristics exhibited by one parent, whether beneficial or harmful, are passed down from one generation to the next (assuming that organism is able to reproduce). Modern Genetics presents a mechanism for heredity.

Darwin’s Case: Key Idea #3 The Inheritance of Traits

Darwin’s Influences: Thomas Mathus Mathus’ An Essay on the Principle of Population emphasized that population growth will always overwhelm growth in food, creating inevitable states of hunger, disease, and competition. This perpetual struggle for survival caught Darwin’s attention, and he applied it to biology. Darwin argued that some of the competitors in Malthus' perpetual struggle scenario would be better equipped to survive. Those that were less able would die out, leaving only those with the more desirable traits.

Darwin’s Influences: Charles Lyell The world’s most renowned geologist of the day and author of author of Principles of Geology, prompted Darwin to think of evolution as a slow process in which small changes gradually accumulate over immense spans of time…

Darwin’s Influences: Jean-Babtiste Lamark Lamarck's proposed the first truly cohesive theory of evolution, in which all organisms had an innate tendency toward perfection. He correctly argued that species change over time, and that environmental forces adapted them to local environments. Lamarck is widely remembered for his inaccurate theory of inheritance of acquired characteristics in which the use and disuse of physiologic features differentiated organisms over time.

What Darwin Couldn’t Know…. Although Darwin had no way of knowing, there is a genetic mechanism for phenotypic change in species over time. Can you guess what this is? Sweet!

Putting it all Together… Survival of the Fittest The ability of an organism to survive and reproduce in its specific environment is fitness. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival.

Survival of the Fittest (cont.) Beneficial adaptations better suit organisms to their environment, and in turn, they’re better able to survive and reproduce. Individuals with characteristics that are not well suited to their environment either die or leave few offspring.

Natural Selection: Decent with Modification Every living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification. Natural selection yields organisms that display different structures, establish different niches, and/or occupy different habitats.

Natural Selection in Action Darwin wondered if animals living on different islands had once been members of the same species. These separate species would have evolved from an original South American ancestor species. His observations of finches, tortoises, iguanas, and other animals supported his hypothesis.

Galapagos Tortoises

Natural Selection in Action: Industrial Melanism and the Peppered Moth Coal burning during the industrial revolution caused the trees in nearby forests to turn dark with soot. Within a short time period, the peppered moth responded… Explain…

3 Key Misconceptions about Darwin’s Theory “Child Please!” “survival of the fittest means only the strongest and fastest survive”… Why is this statement false? How can you change it to make it accurate?

3 Key Misconceptions about Darwin’s Theory “Say What?” “Natural selection is random”… Why is this statement false? How can you change it to make it accurate?

3 Key Misconceptions about Darwin’s Theory “Oh No you didn’t” “Organisms can evolve over their lifetimes”… Why is this statement false? How can you change it to make it accurate?