Natural Selection Darwin’s Big Idea

Charles Darwin (born February 12, 1809) was a British scientist. He sailed around the world as a naturalist, recording what he saw. He made important observations and connections that no scientist had figured out before. You will read more about his discoveries tomorrow.

Natural Selection  The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous)  Charles Darwin ( ) saw three problems in need of a solution.  Darwin was not the only one to notice these problems.  Other scientists, including Alfred Russel Wallace, shared ideas with Darwin and contributed to figuring out the solution.  The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous)  Charles Darwin ( ) saw three problems in need of a solution.  Darwin was not the only one to notice these problems.  Other scientists, including Alfred Russel Wallace, shared ideas with Darwin and contributed to figuring out the solution.

Problem #1  Living things on Earth change over time.  The fossil record shows that in the past there were a lot of plants and animals that are now extinct.  Living things on Earth change over time.  The fossil record shows that in the past there were a lot of plants and animals that are now extinct.

Problem #2  Living things could be classified into different categories.  People were big into classifying stuff.  It was pretty obvious that there was a relationship between different species.  Different birds, different grasses, different cats etc  Living things could be classified into different categories.  People were big into classifying stuff.  It was pretty obvious that there was a relationship between different species.  Different birds, different grasses, different cats etc

Problem #3  Living things have adaptations.  Different kinds of teeth for different animals, say carnivore ripping teeth and herbivore grinding teeth  Different tissues within species  Heart vs. eye etc.  Living things have adaptations.  Different kinds of teeth for different animals, say carnivore ripping teeth and herbivore grinding teeth  Different tissues within species  Heart vs. eye etc.

The Solution!  Darwin figured out a theory that made sense of all of these problems.  He called it Natural Selection.  Darwin figured out a theory that made sense of all of these problems.  He called it Natural Selection.

Darwin’s Logic  Fact 1: Species reproduce exponentially.  Fact 2: Populations stay constant.  Fact 3: Resources are limited.  Inference 1: There must be competition to survive.  Fact 1: Species reproduce exponentially.  Fact 2: Populations stay constant.  Fact 3: Resources are limited.  Inference 1: There must be competition to survive.

Darwin’s Logic  Fact 4: Individuals in a population vary.  Fact 5: Variations are inherited genetically.  Inference 2: Some individuals have traits that help them survive better than others (natural selection).  Inference 3: Over time adaptations accumulate in a populations, creating different species (evolution).  Fact 4: Individuals in a population vary.  Fact 5: Variations are inherited genetically.  Inference 2: Some individuals have traits that help them survive better than others (natural selection).  Inference 3: Over time adaptations accumulate in a populations, creating different species (evolution).

How does it work?  Selection determines which individuals grow up and have babies.  This selection is done by the environment.  The individuals who are best fit to their environment survive and reproduce.  They pass these fit traits on to their offspring.  Selection determines which individuals grow up and have babies.  This selection is done by the environment.  The individuals who are best fit to their environment survive and reproduce.  They pass these fit traits on to their offspring.

The Solution  “Descent with modification from a common ancestor, NOT random modification, but, modification shaped by natural selection.”  Darwin  “Descent with modification from a common ancestor, NOT random modification, but, modification shaped by natural selection.”  Darwin

Misconceptions  Lamarckism  Traits that you develop during your lifetime can be passed on.  Giraffes really wanted leaves, so they stretched their necks and…..  Correction: Individuals cannot evolve.  Lamarckism  Traits that you develop during your lifetime can be passed on.  Giraffes really wanted leaves, so they stretched their necks and…..  Correction: Individuals cannot evolve.

Misconceptions  There is a plan or goal to evolution. Organisms can change because the want to.  Correction: Traits change because of genetics mutations that happen by chance.  There is a plan or goal to evolution. Organisms can change because the want to.  Correction: Traits change because of genetics mutations that happen by chance.