Charles Darwin andCharles Darwin andNatural SelectionNatural Selection

His Ideas and What Shaped His Ideas and What Shaped ThemThem

Chapter 10Chapter 10

Evolution DefinedEvolution Defined

►EvolutionEvolution = change in a = change in a population over timepopulation over time

►Individuals interact with the Individuals interact with the environment, but individuals do environment, but individuals do NOT evolveNOT evolve populationspopulations evolve as the evolve as the

frequency of certain traits / genes frequency of certain traits / genes changeschanges

Charles DarwinCharles Darwin

►Proposed natural Proposed natural selection as a selection as a mechanism for evolutionmechanism for evolution

►Published theory in 1859 Published theory in 1859 – – On the Origin of On the Origin of SpeciesSpecies

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Video #2 – Who Was Charles Darwin?

Charles Charles Darwin, cont’dDarwin, cont’d

► Developed Developed ideas during his ideas during his voyage as a voyage as a naturalist on naturalist on the the HMS BeagleHMS Beagle – particularly as – particularly as a result of his a result of his observations of observations of different different species on the species on the Galapagos Galapagos IslandsIslands

Natural SelectionNatural Selection

► is “differential success” in reproduction is “differential success” in reproduction (some have more success than others)(some have more success than others)

►occurs through interactions between the occurs through interactions between the environment and the variations found environment and the variations found among members of a populationamong members of a population

► leads to populations that are adapted to leads to populations that are adapted to their environmenttheir environment

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Video #4 – “How Does Evolution Really Work?”

Natural Selection - DetailsNatural Selection - Details

►All species have genetic variation.All species have genetic variation.►Variations are heritable (able to be Variations are heritable (able to be

inherited).inherited).►Likelihood of survival depends on Likelihood of survival depends on

traits – and therefore, genes - traits – and therefore, genes - presentpresent

Natural Selection – Details, Natural Selection – Details, cont’dcont’d

► The environment presents challenges The environment presents challenges to organisms and their ability to to organisms and their ability to reproduce.reproduce.

► Organisms produce more offspring Organisms produce more offspring than can survive because of:than can survive because of:

PredationPredation Competition for resourcesCompetition for resources

► Food Food ► WaterWater► ShelterShelter► MatesMates

Natural Selection – Details, Natural Selection – Details, cont’dcont’d

► Individuals Individuals better better adapted to adapted to their their environment environment produce more produce more offspring than offspring than those less those less suited to the suited to the environment.environment.

► The traits of the better adapted individuals tend to The traits of the better adapted individuals tend to become more common in the population over time.become more common in the population over time.

Natural Selection - Details, Natural Selection - Details, cont’dcont’d

►Evolution can only increase or Evolution can only increase or decrease the frequency of decrease the frequency of heritableheritable variations variations if the variation is not passed on, then it if the variation is not passed on, then it

will not be affected by evolution / natural will not be affected by evolution / natural selectionselection

Darwin’s IdeasDarwin’s Ideas

►Many of these ideas were developed during Many of these ideas were developed during Darwin’s voyage on the HMS Beagle and his Darwin’s voyage on the HMS Beagle and his observations of various plant and animal observations of various plant and animal species (especially those on the Galapagos)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’ FinchesGrants’ Finches

► In the 1970s, In the 1970s, Peter and Peter and Rosemary Grant Rosemary Grant studied changes studied changes in finch beak size in finch beak size

► In dry years, In dry years, when berries and when berries and small seeds were small seeds were harder to find, harder to find, average beak average beak depth increased.depth increased.

Other ScientistsOther Scientists

►Darwin was influenced by other Darwin was influenced by other scientistsscientists HuttonHutton LyellLyell MalthusMalthus LamarckLamarck WallaceWallace

James Hutton James Hutton (1785)(1785)

►Proposed gradualism = idea that Proposed gradualism = idea that major changes to Earth can be major changes to Earth can be the result of small changes the result of small changes taking place over long stretches taking place over long stretches of timeof time

►Concluded that Earth must be Concluded that Earth must be millions of years old – as millions of years old – as opposed to thousands of years opposed to thousands of years old, like many people thought at old, like many people thought at the time.the time.

Charles Lyell (1833)Charles Lyell (1833)

►Proposed uniformitarianism = Proposed uniformitarianism = idea that the processes that idea that the processes that happened on Earth in the past happened on Earth in the past are still happening todayare still happening today

►Felt that scientific Felt that scientific explanations for past events explanations for past events must be based on must be based on observations that can be observations that can be made in the presentmade in the present

►Video clip Video clip – 3:25– 3:25

Hutton and LyellHutton and Lyell

►Combined, Hutton and Lyell’s theories Combined, Hutton and Lyell’s theories explained how geological features explained how geological features (mountains, canyons, etc) could be (mountains, canyons, etc) could be created over long periods of timecreated over long periods of time

Hutton and Lyell’s ideas also led to our current understanding of the rock cycle (at left).

Thomas Malthus Thomas Malthus (1798)(1798)

►Studied human population growthStudied human population growth►Predicted that, if left unchecked, the Predicted that, if left unchecked, the

human population would grow so large human population would grow so large that there would not be enough food that there would not be enough food and space for everyoneand 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’dThomas Malthus, cont’d

•Felt that the only things “checking” Felt that the only things “checking” human population growth were war, human population growth were war, famine, and diseasefamine, and disease

Jean Baptiste Lamarck (1809)Jean Baptiste Lamarck (1809)

►Recognized that living things change Recognized that living things change over time, but proposed some over time, but proposed some explanations for this that we now know explanations for this that we now know to be incorrectto be incorrect

►Organisms want to become more Organisms want to become more perfect, so they can “will” a change perfect, so they can “will” a change that will help them be more successfulthat will help them be more successful

Lamarck, cont’dLamarck, cont’d

► Body parts that are used the most Body parts that are used the most grow larger; body parts that are used grow larger; body parts that are used less shrink.less shrink.

““Use and disuse”Use and disuse”

► Acquired traits – changes to an Acquired traits – changes to an organism’s body that happened organism’s body that happened during its lifetime – can be inherited during its lifetime – can be inherited by offspring.by offspring.

““Inheritance of acquired characteristics”Inheritance of acquired characteristics”

► Two different Two different interpretationinterpretationss

► Lamarck’s Lamarck’s interpretation interpretation has not been has not been supported by supported by scientific scientific evidenceevidence

► Darwin’s Darwin’s interpretation interpretation has been has been supported.supported.

Alfred Wallace Alfred Wallace (1858)(1858)

► Independently developed a Independently developed a theory of natural selection theory of natural selection that matches Darwin’s ideasthat matches Darwin’s ideas

►His letter prompted Darwin His letter prompted Darwin to publish his own theory.to publish his own theory.

►Video clip Video clip – 3:50– 3:50