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Natural Selection in Action

Natural Selection in Action. Holt - Chapter 7, Section 3. Foldable Format:. Changes in Populations. Forming a New Species. Changes in Populations: . Changes in populations are sometimes observed when a new force affects the survival of individuals . 1. Adaptation to Hunting

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Natural Selection in Action

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  1. Natural Selection in Action Holt - Chapter 7, Section 3

  2. Foldable Format: Changes in Populations Forming a New Species

  3. Changes in Populations: • Changes in populations are sometimes observed when a new force affects the survival of individuals. 1. Adaptation to Hunting • Ex: Elephant hunting in Uganda • 1930’s – 1% of male elephants did not have tusks • Now – 15% do not

  4. Changes in Populations: 1. Adaptation to Hunting • Why? • People hunt elephants for their tusks. • Fewer survive to reproduce, so more tuskless elephants are born. • They pass this tuskless trait on to their offspring.

  5. Changes in Populations: 2. Resistance to Chemicals

  6. Reading for Meaning • Complete the “Before Reading” column. • Read the article, “Evolution of Antibiotic Resistance.” • Find evidence for or against each of the statements as you read. • Discuss your answers with a partner. • Discuss your answers with the class.

  7. Antibiotic Resistance in Bacteria • Just as insects develop resistance to pesticides, bacteria develop resistance to antibiotics. • Bill Nye – Antibiotics (video clip) • PBS - Antibiotic Resistance

  8. Changes in Populations:3. Competition for Mates • Competition for mates can select for adaptations. • Ex: • In many bird species, females prefer to mate with colorful males. • Colorful males pass on their genes for color to the next generation, so the proportion of colorful males is likely to increase.

  9. Forming a New Species • Species – a group of organisms that can mate with each other to produce fertile offspring. • A new species may form after a group becomes separated from the original population. • Over time, the new population adapts to its new environment. • Eventually, the two populations differ so much that they can no longer mate successfully. • Speciation – the formation of a new species as a result of evolution.

  10. Forming a New Species

  11. 3 Steps in Forming a New Species • Separation • Population becomes separated from the rest • Ex: physical barriers such as canyons, mountains, or lakes • Adaptation • Populations constantly undergo natural selection • Adaptations in the separated populations differ • Division • The separated groups evolve and become different from each other • No longer able to interbreed – two different species now

  12. Summary • In Australia, many animals look like mammals from other parts of the world. But most of the mammals in Australia are marsupials (mammals that carry their young in a pouch after birth). Few kinds of marsupials are found anywhere else in the world. • What is a possible explanation for the presence of so many of these unique mammals in Australia?

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