Transcript Document

Unit B: Life Over Time
Chapter 6: Evolution of Living Things
6.1 Earth has been home to living things for about 3.8
billion years
6.2 Species change over time
6.3 Environmental changes can affect populations
6.4 Many types of evidence support evolution
6.2 Species change over time
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Before, you learned:
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Fossils are evidence of earlier life
More complex organisms have developed over time
Mass extinctions contributed to the development of Earth’s
history
Now, you will learn:
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About early ideas and observations on evolution
How Darwin developed his theory of natural selection
How new species arise from older species
Scientists explore the concept of
evolution
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Evolution ~ a gradual change over time
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“The process through which species change over
time”
This change is a result of the change in the
genetic material of an organism and is inherited
(passed from one generation to the next)
Scientists explore the concept of
evolution
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Early Ideas
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Early 1700s: scientists could see species
change over time…but how
Jean-Baptiste de Lamarck:
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French, early 1800s
proposed that species have changed over
time
Based on the idea an individual
organism can acquire a new trait during
a lifetime and pass it down
Ex: giraffes stretched their necks to reach
leaves, passing this trait for long necks to
their offspring
What is missing here?
Evidence!
Scientists explore the concept of evolution
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Darwin’s Observations (1809-1882)
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Spent 5 years on board the Beagle:
sailed from England, along the coast of
South America – studied rock
formations, fossils, and life
18 Galapagos Islands: plants and
animals not only differed from those on
the mainland, but also between islands
Alfred Russel Wallace –
proposed similar ideas
around the same time
Darwin’s Observations
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Observed several types of tortoises on the islands
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Short necks in damp areas with plentiful plant life
Longer necks in dry areas with cacti
Finches, beak shapes and sizes
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Heavy, short beaks for pecking trees
Small, thin beaks for capturing insects
Natural Selection explains how living
things evolve
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Darwin struggled to develop an explanation that would account for the
diversity he saw
Breeders can produce new variations of an animal over time: artificial
selection
 New breed: select dogs with a certain trait – mate
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Darwin: Similar process occurring in nature:
 Natural Selection – members of a species that are best suited to their
environment survive and reproduce at a higher rate than other members
of the species
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Resulting litter: again selectively breed…until a new breed is produced
Based on: overproduction, variation, adaptation, and selection
* both artificial and natural selection have similar results: desired results are passed
from one generation to the next…they differ in that humans control one process and
the other is due to natural processes
*Theory: a well-tested explanation based on a broad range of facts and observations
– not proven, but are generally accepted to be true
Natural Selection explains how living things evolve
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Overproduction:
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A plant or animal that reproduces usually makes more offspring than can possibly
survive (than the environment can support):
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These are passed on from one generation to the next
Genetic material may change – new variation (mutation)
Reproduction: passes these traits to offspring
Adaptation
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A mutation can make an individual better able to survive
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Genetic variation: differences in DNA in a population
Species have natural differences/variations in traits – ex: fin size
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Ex: several thousand salmon eggs, not all hatch, a few hundred survive disease or
predation, several dozen reach adulthood, and few will successfully reproduce
Variation
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Population: group of individuals of the same species that live
in a particular environment or area
An advantage in the particular environment; ex: tail shape – swim faster
Selection
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Environmental factors: conditions that affect survival – include
food supply, habitat, predators, and disease
Particular adaptations lead to survival long enough to reproduce
That adaptation becomes more common in the next generation of offspring
Darwin’s Theory of Evolution by
Natural Selection
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basic idea – “Descent with modification”
Although some details were absent (or underdeveloped because he couldn’t know, for
example, the structure of DNA and the
mechanism of inheritance), Darwin’s
fundamental ideas have been supported by
overwhelming evidence from morphological,
biochemical, fossil, behavioral, and direct
observational data
New species develop from earlier
species
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In 1859, after more than 20 years of work, Darwin published, On the Origin of
Species
Speciation:
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Evolution of new species from an existing species
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Environmental changes (rapid or gradual)
Ex: in book Lake Tanganyika: over 150 cichlid species pB24
Isolation:
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Darwin’s trip to the Galapagos: islands were separated from the mainland by miles of
ocean, ad unable to breed with mainland relatives
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Today: isolation is essential to speciation – for species to separate, two populations
must be prevented from reproducing with each other
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New species evolved
Darwin: isolation of population by geographical or other barriers could contribute to the
process of speciation
Geographic boundary – ocean, mountain range, feed on different things, reproduce at
different times of the year
Mutations in one isolated group may differ from another…two populations may evolve
differently from each other  Speciation  BIODIVERSITY on Earth