Evolution

Take notes and make sure you write down the vocabulary

(bold words in this PowerPoint)

Evolution

• Evolution- the process by which organisms change over time.

Four Factors

• There are four factors that affect if evolution occurs. • Factor #1- The organism has to have genetic variability

due to mutations and genetic recombination. • Genetic recombination is caused by crossing over in

meiosis where genetic material can be traded between chromosomes.

• Basically- there has to be some difference genetically between organisms in the same species (example bird beak type)

Four Factors

• Factor #2- The population has the potential to increase it’s numbers.

• Basically- the population has to be able to reproduce or the genetic variation would not get passed on.

Four Factors

• Factor 3- There has to be a finite supply of resources.

• Basically- there has to be enough resources like food and shelter for the population to be able to reproduce and live.

Four Factors

• Factor #4- Natural selection by the environment for those offspring better able to survive and produce offspring.

• Natural Selection- process by which organisms with variations most suited to their local environment survive and leave more offspring.

• Basically- the organisms that can have traits that allow them to survive produce more offspring so their traits get passed on.

Natural Selection

• There are four factors that have to be present for natural selection to occur

• #1- There has to be variation between individuals in the population

• - There has to be different traits present in a population. These variations must be genetic variations that can be passed on to offspring

Natural Selection

• #2- There has to be competition for resources (food, mates, shelter, etc)

• Struggle for existence- members of each species compete regularly to obtain food, living spaces, and other necessities of life.

Natural Selection

• #3- This competition would lead to the death of some individuals and while others would survive. (survival of the fittest)

• Fitness- ability of an individual to survive and reproduce in its specific environment

Natural Selection

• #4- Individuals that have advantageous variations will more likely survive and reproduce.

• Advantageous variation = adaptation• Adaptation- inherited characteristic that

increases an organism’s chance to survival. • individuals that have an adaptation will survive

and reproduce and pass along that adaptation to offspring

• Say in a species of blob….there exists blobs of all shapes and sizes (variation)

Blobs eat the little purple organisms that live underground and on the surface.

During a particularly hot year, food became less abundant (competition), blobs that had the ability to dig into the soil to get food had a better chance of survival.

Many blobs died that year…….

The ones that survived mated and passed their genes to the next generation. (reproduction)

The next generation had move blobs with the pointed noses. That is NATURAL SELECTION.

1. Variation2. Competition3. Survival4. Reproduction

Common Descent

• Darwin proposed that species living today are descended from older species that survived and reproduced.

• Over time these older species evolved into new species called descent with modification (change)

• It can take thousands or even millions of years for a new species to evolve.

• If you go back far enough all organisms are related and came from a common ancestor this is called common descent.

Evidence for Evolution

• Evidence for the process of evolution can be found in the fossil record, homologous structures of living organisms, similarities in early development, or embryolgy, and DNA

Fossil Evidence• Shows numbers extinct animals• Shows similarities between extinct animals and animals that are alive today• The earth’s layers show a time scale of species and when they appeared on earth

(and when they died out)

• Homologous structures – these are parts of the body that are similar, but have different functions

ex. The flippers of whales, and the wings of birds

All forelimbs of vertebrates have the same pattern of bones

• Common ancestry

• Vestigial Organs – these are organs or parts that seem to have no function

Whales have pelvic bones that do not attach to legs

Embryological DevelopmentEmbryos of different species develop in almost identical ways.

Human fetus at 8 weeks

• Biochemistry and DNA

When comparing the DNA of one species to another, more similarities are found in species that are more closely related.

Lion photo credit: ucumari Tiger photo credit: digitalART2

Direct observation of species change 1.Bacteria become resistant to antibiotics2.Wolves were bred over many generations to

become dogs (artificial selection) • and then bred further to create a variety of breeds

Questions- answer in notebook

• #1 What are the four factors that affect evolution?

• #2 What is natural selection?• #3 What are the four factors that have to be

present for natural selection to occur?• #4 What is the theory of common descent?• #5 What is the evidence supporting the theory

of evolution?