Darwin & Natural Selection Evolution Unit

Learning Goals 1. Define "Evolution" & "Natural Selection". 2. Describe the 4 steps of Natural Selection, giving an example of each. 3. Explain the importance of "Variation". 4. Explain how environmental changes can trigger evolution

Theory of Evolution Evolution: The process of change over time Specifically, a change in the frequency of a gene or allele in a population over time (it’s all about the DNA!)

Evolution vs. Natural Selection They are not the same thing! Evolution – is the “what” (organisms changing over time) Natural Selection is the “how” (the mechanism that causes the changes)

Charles Darwin Father of Evolution Darwin went on a 5-year trip around the world on the ship, the HMS Beagle As the ship’s naturalist, he made observations of organisms in South America and the Galapagos Islands

What did Darwin’s travels reveal? The diversity of living species was far greater than anyone had previously known!! Species separated on different islands, while similar, had different traits

How did tortoises and birds differ among the islands of the Galapagos? Each island had its own type of tortoises and birds that were clearly different from other islands

Galapagos Tortoises

Darwin’s Travels These observations led him to develop the theory of evolution!! He proposed that natural selection was the mechanism for evolution He wrote a book called “The Origin of Species”

Natural Selection Organisms that inherit advantageous traits will reproduce more successfully

4 Steps of Natural Selection Darwin’s Theory of Natural Selection occurs in four steps: Overproduction Genetic Variation Competition Selection

1. Overproduction Each species produces more offspring than can survive Only some will survive to grow up and reproduce (passing on their genes)

2. Genetic Variation Each individual has a unique combination of inherited traits (in the DNA/genes). If an organism has a trait that helps it survive and reproduce, we call it an adaptation

What adaptations do you see?

What adaptations do you see?

Why is Variation Important? Because the environment changes. The more variation within a species, the more likely the species will survive If everyone is the same, they are ALL vulnerable to the same environmental changes or diseases Organisms that cannot evolve to adapt to a changing environment, will become extinct.

3. Competition Individuals COMPETE for limited resources: Food, water, space, mates Natural selection occurs through “Survival of the Fittest” Fitness: the ability to survive and reproduce Not all individuals survive to adulthood Starvation, sickness, eaten by predators

“Survival of the Fittest” It’s not always the biggest, or the strongest, or the fastest, or the smartest! It’s simply the one that is best able to survive in the environment

4. Selection The individuals with the best traits / adaptations will survive and have the opportunity to pass on their traits to offspring. Those traits will increase in the population

4. Selection The individuals that do not survive will not pass on their traits. Those traits will decline (go down) or disappear in the population

Selection Individuals with traits that are not well suited to their environment either die or have fewer offspring. Evolution occurs when successful traits build up in a population over many generations and unsuccessful traits are eliminated by the death of the individuals. The successful traits have been “selected” ✔ ✗

Gene Pool The gene pool is all of the different traits in the population

Gene Pool The gene pool will change as some traits are added (through mutation), successful traits increase, and unsuccessful traits decrease

What natural selection is NOT It is NOT a change during an organism’s lifetime It is caused by the traits that an organism is born with…found in the genes/DNA It is NOT a conscious act Organisms do not “try” to adapt. They only try to survive and reproduce! It is NOT random chance There are traits that are more likely to get passed on, because they are the best fit for the environment

Peppered Moths A famous example of an environmental change causing evolution Click here to watch a Youtube clip: http://www.youtube.com/watch?v=LyRA807djLc

Peppered Moth A Which moth will the bird catch? B

Learning Goals 1. Define "Evolution" & "Natural Selection". 2. Describe the 4 steps of Natural Selection, giving an example of each. 3. Explain the importance of "Variation". 4. Explain how environmental changes can cause evolution