natural selection in action
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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 - PowerPoint PPT PresentationTRANSCRIPT
Natural Selection in Action
Holt - Chapter 7, Section 3
Foldable Format:
Natural Selection in Action
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• Ex: Elephant hunting in Uganda– 1930’s – 1% of male elephants did not have tusks– Now – 15% do not
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.
Changes in Populations: 2. Resistance to Chemicals
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.
Antibiotic Resistance in Bacteria
• Just as insects develop resistance to pesticides, bacteria develop resistance to antibiotics.
• Bill Nye – Antibiotics (video clip)• PBS - Antibiotic Resistance
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.
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.
Forming a New Species
3 Steps in Forming a New Species
1. Separation– Population becomes separated from the rest– Ex: physical barriers such as canyons, mountains, or lakes
2. Adaptation– Populations constantly undergo natural selection– Adaptations in the separated populations differ
3. Division– The separated groups evolve and become different from
each other– No longer able to interbreed – two different species now
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?