Evolution

•Scientists believe that all living organisms on earth share a common ancestor.

•Newer species arise from older species by evolution.

•Evolution is the process by which populations accumulate inherited changes over many, many generations.

How does evolution happen?

________________, born in 1810, is credited with the first theory explaining evolution.

Charles Darwin

Darwin observed that different species of birds were uniquely adapted to their environment.

_____________ - a group of organisms that can mate with one another to produce fertile offspring.

species

_______________ – a characteristic that helps an organism

survive and reproduce in its environment

examples: ________________________________________

________________________________________

adaptation

Sharper teeth to eat meat,

lungs to live on land, longer neck to reach food

He learned from plant and animal breeders.

They could select for desirable traits by picking what animals will breed together.

He reasoned that this could happen in nature but it wouldtake MUCH longer.

He learned about populations.

Species can produce too many offspring but starvation, disease, war, and predators limit the population size. So there must be something special about the survivors—they must inherit traits that help them survive in their environment.

Darwin proposed that evolution occurred by

_____________________ acting on the adaptationsnatural selection

Darwin’s theory of Evolution by Natural Selection

the process by which organisms with favorable traits survive and reproduce more than organisms without thefavorable trait.

__________________- more offspring are produced than can survive

overproduction

__________________- there is variation within the traits in a population; some individuals in a population are better able to survive than others because of their traits

Genetic Variation

__________________- the environment does not have enough food, water, and other resources to support every individual; there is going to be competition for survival within a population and not all individuals will survive to adulthood

Struggle to survive

_______________________- The individuals with the favorable adaptations will be more successful at producing offspring and eventually will take over the population

Successful reproduction

How has evolutionary theory changed since Darwin?

Darwin didn’t know anything about genes. Now we know that it is changes in the DNA or mutations that cause the variation in a population.

________________ - changes in the DNAmutation

mutations lead to the variations or differences in the genes which then cause differences in traits

sometimes those differences can cause an individual in the population to survive better.

Evidence supporting the theory of evolution

1. _______________

__________ – solidified remains or imprints of once-living organisms

Using fossils, scientists have constructed a fossil record or historical sequence of life.

Gaps exist but they are being filled in all time.

Fossil record

fossils

2. ___________________

Vestigial structures are remnants of structures that had a useful role at one time but no longer do.

The presence of these structures suggests that the organism evolved from another life form where that structure played a more important role.

examples:

_________________________________________________

_________________________________________________

Vestigial structures

remnants of hind-limb bones in whales and some snakes

tailbone in humans

3. comparing organisms that are alive today

a. ___________________ – bone structures of mammals are very similar suggesting a common origin (see figure 9 on .156 in your textbook)

Skeletal structures

b. ________ – all living organisms have the same genetic material

organisms that are more closely related have DNA that is more similar

example: human and chimp genes are ~ _________% identical

human and mouse genes are ~ _________% identical

98

70

DNA

c. _________ – cells are the basic unit of all life; all living organisms start from a single cell

cells