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 (1809-1882) 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.
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
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.
The Solution! • 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.
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).
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.
The Solution • “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.
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.