Transcript Darwin and Natural Selection

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.