Evolution by Natural

SelectionHour 2, 2-23-2011

Learning Targets for Evolution

8.1 I can define evolution and use the definition to predict where modern

organisms have come from.

8.2 I can recognize that evolution requires a long period of time to occur.

8.3 I can compare artificial selection to natural selection and am able to

identify each from examples.

8.4 I can identify the two major sources of variation in organisms that

reproduce sexually.

8.5 I can explain why genetic variation within a population is essential for

change over time.

8.6 I can list examples of challenges that organisms face in their struggle

for existence.

8.7 I can explain why organisms compete with one another in order to

survive.

8.8 I can define the term adaptation.

Learning Targets Continued… 8.9 I can predict what will happen when organism’s adaptations are more suited to

their environment.

8.10 I can describe the difference between an individual and a population and state

which is affected by evolution.

8.11 I can differentiate between the concept of an adaptation and the process of

evolution.

8.12 I can predict how an adaptation will change in frequency within the population

over time.

8.13. I can use graphical data to describe how the frequency of a particular trait will

change in response to different natural selection pressures.

8.14 I can explain convergence in terms of how unrelated species respond to similar

environmental pressures.

8.15 I can use the process of natural selection to explain how divergence and

adaptive radiation lead to diverse populations from one common ancestor.

8.16 I can use co-evolution to explain what will happen to two organisms that are

closely connected to each other

Why should we study evolution?

Important TermsEvolution Artificial selectionNatural selectionVariationCompetitionAdaptationConvergence

Divergence Adaptive

radiation Co-evolution Theory

What is a Theory? Theory- a well-substantiated

explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses

Law- a descriptive generalization about how some aspect of the natural world behaves under stated circumstances and that carries the weight of scientific evidence

Fact-an observation that has been repeatedly confirmed

Hypothesis- a testable statement about the natural world

Belief- a psychological state in which a person holds a premise (or statement) to be true.

Evolution by Natural Selection is a theory

Evolution (or change in organisms over time) is a scientific theory; it is a well-substantiated explanation of an aspect of the natural world that incorporates facts (observable phenomena) such as virus and bacterial adaptations, inferences (geological processes have always been happening at a constant rate in the history of the Earth), and tested hypotheses (evolutionary relationships echoed in DNA analysis).

Age of the Earth Earth is about 4.5

billion years old Geologists

confirmed this approximate date through determining the age of rock formations and the time it would take for them to form

Why does it matter how old the Earth is?

Time is important: If weathering and other geological

processes have been happening at the same rate for a very long time (or always) then the Earth must be several billion years old to account for the formations.

Other ways we know: Chemical analysis of ice cores radio active fluorine

Evolution Change in organisms over

time

These changes are seen in populations not in individuals

Charles Darwin On the Origin of Species in 1859. Darwin supplied evidence that

evolution has occurred. He also explained his ideas about how (mechanism) evolution occurs.

Darwin’s theory was based on artificial selection. In artificial selection, nature provided the variation, and humans selected those variations that they found useful.

For example, animal breeders used only the largest hogs, fastest horses, or cows that produced the most milk for breeding.

Artificial Selection

Variation in traits exists

Breeder selects favorable traits in organism

Breeder mates animals with the favorable traits more than other organisms

Desired traits become more common in population

Natural Selection

Variation in traits exists

Nature “selects” favorable traits in organism because some of these trait give a reproductive or survival advantage

Organisms with favorable traits survive better and have more offspring

Traits that give a reproductive/survival advantage become more common in population

Why do both forms of selection require

variation?

Sources of variation

Genetic Shuffling in Anaphase I of meiosis

Mutation to DNA passed down to offspring (very rare!)

What is competition?

Competition Competition is a struggle for limited

resources in which there can only be one or a few “winners”

On Earth we have a finite number of resources; there are many more organisms than resources.

A struggle for survival results, the organisms that get the resources will live and pass on their genes to the next generation.

Besides limited resources; what are some other challenges organisms must face to survive and reproduce?

Adaptations Traits that

provide some type of advantage to organisms in the struggle for survival are called adaptations.

There are recognizable patterns to the way organisms adapt

Predict what will happen to a bunny population with a

brown fur mutation in an equatorial environment.

Convergence

Unrelated species respond to environmental pressures with similar functional adaptations

Divergence Humans DID

NOT come from apes, rather both species had a common ancestor long ago

IDA

Draw a diagram of how scientist would

describe the relationship between

Ida, humans and apes.

Adaptive Radiation

Adaptive radiation is the pattern of adaptation that isolates a species into two separate lineages

Co-Evolution Co-evolution is

when a species directly influences the evolution of another species and both populations evolve in parallel.