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Charles Darwin and Natural Selection His Ideas and What Shaped Them Chapter 10
Evolution Defined ► Evolution = change in a population over time ► Individuals interact with the environment, but individuals do NOT evolve populations evolve as the frequency of certain traits / genes changes
Charles Darwin ► Proposed natural selection as a mechanism for evolution ► Published theory in 1859 – On the Origin of Species http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Video #2 – Who Was Charles Darwin?
Charles Darwin, cont’d ► Developed ideas during his voyage as a naturalist on the HMS Beagle – particularly as a result of his observations of different species on the Galapagos Islands
Natural Selection ► is “differential success” in reproduction (some have more success than others) ► occurs through interactions between the environment and the variations found among members of a population ► leads to populations that are adapted to their environment http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Video #4 – “How Does Evolution Really Work?”
Natural Selection - Details ► All species have genetic variation. ► Variations are heritable (able to be inherited). ► Likelihood of survival depends on traits – and therefore, genes - present
Natural Selection – Details, cont’d ► The environment presents challenges to organisms and their ability to reproduce. ► Organisms produce more offspring than can survive because of: Predation Competition for resources ► Food ► Water ► Shelter ► Mates
Natural Selection – Details, cont’d ► Individuals better adapted to their environment produce more offspring than those less suited to the environment. ► The traits of the better adapted individuals tend to become more common in the population over time.
Natural Selection - Details, cont’d ► Evolution can only increase or decrease the frequency of heritable variations if the variation is not passed on, then it will not be affected by evolution / natural selection
Darwin’s Ideas ► Many of these ideas were developed during Darwin’s voyage on the HMS Beagle and his observations of various plant and animal species (especially those on the Galapagos)
Darwin observed a lot of variation in beak size / shape among finches on the Galapagos The variations that were more common on certain islands seemed to be related to the type of food that was available.
Grants’ Finches ► In the 1970s, Peter and Rosemary Grant studied changes in finch beak size ► In dry years, when berries and small seeds were harder to find, average beak depth increased.
Other Scientists ► Darwin was influenced by other scientists Hutton Lyell Malthus Lamarck Wallace
James Hutton (1785) ► Proposed gradualism = idea that major changes to Earth can be the result of small changes taking place over long stretches of time ► Concluded that Earth must be millions of years old – as opposed to thousands of years old, like many people thought at the time.
Charles Lyell (1833) ► Proposed uniformitarianism = idea that the processes that happened on Earth in the past are still happening today ► Felt that scientific explanations for past events must be based on observations that can be made in the present ► Video clip – 3:25 Video clip Video clip
Hutton and Lyell ► Combined, Hutton and Lyell’s theories explained how geological features (mountains, canyons, etc) could be created over long periods of time Hutton and Lyell’s ideas also led to our current understanding of the rock cycle (at left).
Thomas Malthus (1798) ► Studied human population growth ► Predicted that, if left unchecked, the human population would grow so large that there would not be enough food and space for everyone http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html Video Clip from “Darwin’s Dangerous Idea” – connection between Malthus’ theory on humans and other animals’ population size.
Thomas Malthus, cont’d Felt that the only things “checking” human population growth were war, famine, and disease Felt that the only things “checking” human population growth were war, famine, and disease
Jean Baptiste Lamarck (1809) ► Recognized that living things change over time, but proposed some explanations for this that we now know to be incorrect ► Organisms want to become more perfect, so they can “will” a change that will help them be more successful
Lamarck, cont’d ► Body parts that are used the most grow larger; body parts that are used less shrink. “Use and disuse” ► Acquired traits – changes to an organism’s body that happened during its lifetime – can be inherited by offspring. “Inheritance of acquired characteristics”
► Two different interpretations ► Lamarck’s interpretation has not been supported by scientific evidence ► Darwin’s interpretation has been supported.
Alfred Wallace (1858) ► Independently developed a theory of natural selection that matches Darwin’s ideas ► His letter prompted Darwin to publish his own theory. ► Video clip – 3:50 Video clip Video clip