Theory of Natural Selection

Darwin Proposed the Theory of Natural Selection to Explain Evolution

Evolution, or change over time, is the process , or change over time, is the process by which modern organisms have descended by which modern organisms have descended from ancient organisms. from ancient organisms.

A scientific A scientific theory is a well-supported testable is a well-supported testable explanation of phenomena that have occurred explanation of phenomena that have occurred in the natural world.in the natural world.

Ideas that Shaped Darwin’s Thinking

James Hutton:James Hutton: Proposed a theory of Proposed a theory of geological changegeological changeStates that natural States that natural forces change earth’s forces change earth’s surface shapesurface shapeStates that these States that these changes are slow and the changes are slow and the Earth was much older Earth was much older than thousands of yearsthan thousands of years

Ideas that Shaped Darwin’s Thinking

Charles LyellCharles Lyell Wrote the book Wrote the book ““Principles of Principles of Geography”Geography”States that geographical States that geographical features can be built up features can be built up or torn downor torn downDarwin thought if earth Darwin thought if earth changed over time, what changed over time, what about life?about life?

Ideas that Shaped Darwin’s Thinking

Jean Baptist LamarkProposed that species Proposed that species change with a tendency change with a tendency toward perfection (Giraffe toward perfection (Giraffe necks)necks)Traits that are used are Traits that are used are passed down to offspringpassed down to offspringTraits that are not used are Traits that are not used are not passed downnot passed down

Thomas MalthusThomas Malthus19th century English 19th century English economist who wrote economist who wrote “On the Principle of “On the Principle of Population”Population”Stated that if a Stated that if a population grew too population grew too large, then there would large, then there would be insufficient living be insufficient living space and a lack of food space and a lack of food so population would so population would declinedecline

Ideas that Shaped Darwin’s Thinking

• Populations tend to rise and fall overtime

• As the population decreases, food supply returns

• As food supply returns, population grows again

Selective Breeding-Selective Breeding-The process of humans selecting traits The process of humans selecting traits they want to appear in offspring to produce they want to appear in offspring to produce desired traitsdesired traitsUsed in farming to create sheep with fine Used in farming to create sheep with fine woolwoolUsed to create different breeds of dogs Used to create different breeds of dogs and catsand cats

Ideas that Shaped Darwin’s Thinking

Russell WallaceRussell Wallace wrote an essay wrote an essay summarizing summarizing evolutionary change evolutionary change from his field work in from his field work in MalaysiaMalaysia

Gave Darwin the drive Gave Darwin the drive to publish his findings to publish his findings

Ideas that Shaped Darwin’s Thinking

Darwin’s Conclusion:Evolution happens through the

process of natural selection!

Also called “Survival of the Fittest”Also called “Survival of the Fittest”Some individuals are better suited for their Some individuals are better suited for their environmentenvironmentThese individuals will survive and reproduce These individuals will survive and reproduce better than the othersbetter than the othersThese favorable traits will be passed down in These favorable traits will be passed down in offspring and appear more in future generationsoffspring and appear more in future generations

Natural Selection

Over time, natural Over time, natural selection results in selection results in changes in inherited changes in inherited characteristics of a characteristics of a population. population.

These changes These changes increase a species increase a species fitness in its fitness in its environmentenvironment

Requirements for Natural Selection

Overproduction: There must an overproduction of offspring so that some can live while others will die.

Requirements for Natural Selection

Genetic Variation: There must be differences among the individuals so that some do better than others.

Ex. Color, aggression, intelligence, behaviors, speed

Requirements for Natural Selection

Competition: There must be a struggle to survive due to limited resources.

Ex. Limited resources could include food, water, shelter, mates, territory

Requirements for Natural Selection

Successful Reproduction: There must be successful individuals who pass down their favorable traits to offspring.If none are able to, then the

population will go extinct!