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Scientists explore the concept of
evolution
 Evolution ~ a gradual change over time
 “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
 Early Ideas
 Early 1700s: scientists could see species
change over time…but how
 Jean-Baptiste de Lamarck:
 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
 Darwin’s Observations (1809-1882)
 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
 Observed several types of tortoises on the islands
 Short necks in damp areas with plentiful plant life
 Longer necks in dry areas with cacti
 Finches, beak shapes and sizes
 Heavy, short beaks for pecking trees
 Small, thin beaks for capturing insects
Natural Selection explains how
living things evolve
 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
 Resulting litter: again selectively breed…until a
new breed is produced
Natural Selection Explains
how Things Evolve
 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
 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
 Overproduction:
Population: group of individuals of the same species that live
in a particular environment or area
 A plant or animal that reproduces usually makes more offspring than can possibly
survive (than the environment can support):
 Ex: several thousand salmon eggs, not all hatch, a few hundred survive disease or
predation, several dozen reach adulthood, and few will successfully reproduce
Genetic variation: differences in DNA in a population
 Variation
 Species have natural differences/variations in traits – ex: fin size
 These are passed on from one generation to the next
 Genetic material may change – new variation (mutation)
 Reproduction: passes these traits to offspring
 Adaptation
 A mutation can make an individual better able to survive
 An advantage in the particular environment; ex: tail shape – swim faster
 Selection
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
 basic idea – “Descent with modification”
 Although some details were absent (or under-developed
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
 In 1859, after more than 20 years of work, Darwin published,
On the Origin of Species
 Speciation:
 Evolution of new species from an existing species
 Environmental changes (rapid or gradual)
 Ex: in book Lake Tanganyika: over 150 cichlid species
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New Species Develop from
Earlier Species
 Isolation:
 Darwin’s trip to the Galapagos: islands were separated
from the mainland by miles of ocean, ad unable to breed
with mainland relatives
 New species evolved
 Darwin: isolation of population by geographical or other
barriers could contribute to the process of speciation
 Today: isolation is essential to speciation – for species to
separate, two populations must be prevented from
reproducing with each other
 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