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Charles Darwin and Natural Selection

Date: _________

Who is Charles Darwin?

• Began the voyage of the Beagle in 1831

– Collected fossils and observed many different types

of wildlife to and from the Galapagos islands

• 1836: came up with the theory of natural

selection, returned to England

• 1859: joint publication of the same theory

with Alfred Russel Wallace

– Book was titled On the Origin

of the Species

So did he really say that…? NO! • Humans did not come from monkeys,

nor did we come from chimps or any

other primate.

• We share common ancestors.

• Well, what’s the difference?

–We did not come

from primates

because primates are

still here.

– It works something

like this…

What is Evolution? • It describes all of the changes that

have transformed life on Earth from its

earliest beginnings to what we see in

the world today.

• It’s a BIG DEAL – probably the biggest

thing about

biology!

• It’s tied in with

EVERYTHING ELSE

we’ve talked about!

Wait…there are types?

• Microevolution

– Small-scale evolution

that only affects a

single population

• Macroevolution

– Large-scale evolution

that affects the entire

species across

multiple populations

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Evolution by Natural Selection

• Natural selection occurs because

individuals in a population have

different traits that allow them to

survive in the environment more

efficiently than others without these

traits.

– Results in changes in

inherited traits of a

population over time.

– These changes increase a

species’ fitness in its

environment.

Four Principles of Natural Selection

• Overproduction of offspring

• Variation

• Adaptation

• Descent with modification

Overproduction of Offspring • How can it lead to natural

selection?

– If a population can have many

offspring, it raises the chance that

some will survive.

• The bad news:

– It can increase

competition for

resources.

Variation • What kind of variation exists in this room

right now?

– All kinds! An organism’s phenotype may

influence its ability to find, obtain, or use

resources like food, water,

shelter, and oxygen – it may

even affect the ability to

reproduce!

• Phenotypic variation is

controlled by the organism’s

genotype and the

environment.

– Bad phenotype = death

Adaptation

• Adaptation increases the frequency of a

particular structure, process, or behavior; it

makes the organism able to better survive

and reproduce.

– Good adaptations are passed on while bad

adaptations probably won’t be.

– This leads to a change in the gene pool over time.

• And just when you may have forgotten about

him…

– Fitness is used to measure how successful a trait is

in an environment based on how well it contributes

to reproduction.

Descent with Modification • When the environment changes, natural

selection can shape new populations with new

phenotypes adapted to new conditions.

• Natural selection can produce

populations with different

structures or that live in

different habitats from their

ancestors – descent with

modification!

• More individuals will have

successful traits in later

generations as long as those

traits help the organism survive.

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“I’m simply saying that life…finds a way.”

But Wait…There’s More! • What types of organisms pass on

genetic information to offspring

through reproduction?

–All of them!

• What are the types of reproduction?

– Sexual reproduction

–Asexual reproduction

What’s the Difference? • Sexual reproduction uses meiosis to

create gametes. Fertilization results in

the embryo receiving alleles from each

parent for every trait, and the individual

expresses a combination of

traits.

–Genetic variability is also a

result of…

• Gene shuffling

• Crossing over

• Mutations

• Asexual reproduction involves only one

parent producing offspring that are

basically genetically identical to the

parent.

– Occurs via binary fission (single-celled

organisms) or mitosis (multicellular

organisms)

– Genetic variability

only occurs via

• Mutations in the DNA

passed from parent to

offspring

Which one is better?

SEXUAL

Lower reproduction

rate

Fewer offspring are

produced at a time

Offspring vary greatly

from one another

ASEXUAL

Higher reproduction

rate

Many offspring are

produced at a time

Offspring are

genetically identical

An organism that can reproduce both sexually AND asexually have a great adaptive

advantage for survival!

Methods of

reproduction

Genetic

variability