Transcript Natural Selection and the Evidence for Evolution

Natural Selection and the
Evidence for Evolution
The theory of evolution is the most fundamental
concept in biology.
What is the origin of evolution?
• Fossil records have been important to
science since the 18th century.
• Fossils have formed concepts & answers
questions
• Several ideas have been proposed but only 1
ideas accepted today by scientists.
Charles Darwin (1809-1882)
• English scientists-founder of
modern evolutionary theory
• 1831 – naturalists
• Collect, study & store specimens while on
ship Beagle
• Developed theory to explain how evolution
occurs
HMS Beagle
Darwin on HMS Beagle
Snoppy discovers Darwin's "Voyage of the Beagle"
is not about his trip to mall, but about biological
evolution
Darwin on the HMS Beagle
• He began in 1831 at
age 22 when he took a
job as a naturalist on
the English ship HMS
Beagle, which sailed
around the world on a
five-year scientific
journey.
• As the ship’s naturalist,
Darwin studied and
collected biological and
fossil specimens at every
port along the route
• For the next 20 years,
Darwin’s work refined his
explanations for how
species change over time.
In the Galapagos
• On the Galapagos Islands, Darwin studied many
species of animals and plants that are unique to the
islands but similar to species elsewhere.
• He realized that individuals struggle to compete in
changing environmental conditions.
Darwin continues his studies
How did this help Darwin?
• He knew that many species produce large
numbers of offspring.
• He also knew that such species had not
overrun Earth.
• Only some individuals survive the
competition and produce offspring
Galapagos tortoise are the largest
On Earth, different from other
Tortoises in body size and shape
Galapagos finch
Is adapted to feed
On cacti.
Galapagos marine iguanas
Eat algae from the ocean
Large claws help to cling
To slippery rocks
Artificial Selection
artificial selection is the process of intentional or unintentional
modification of a species through human actions which encourage
the breeding of certain traits over others
Darwin hypothesis that there was a force in nature that worked like
artificial selection
Natural Selection
• Natural selection is a
mechanism for change in
populations.
• It occurs when organisms
with favorable variations
survive, reproduce, and
pass their variations to the
next generation.
• As a result, each
generation consists largely
of offspring from parents
with these variations that
aid survival.
• In nature, organisms
produce more offspring
than can survive
• Darwin proposed this idea
of natural selection to
explain how species
change over time
Darwin explains natural selection
• In any population,
individuals have
variations. Fishes, for
example, may differ
in color, size, and
speed.
Darwin explains natural selection
• Individuals with certain useful
variations, such as speed,
survive in their environment,
passing those variations to the
next generation.
Darwin explains natural selection
• Over time, offspring with
certain variations make up
most of the population and
may look entirely different
from their ancestors.
Adaptations for Evolution
• According to
Darwin’s theory,
adaptations in
species develop
over many
generations.
Structural adaptations arise over time
• Learning about adaptations in mole-rats can help
you understand how natural selection has affected
them.
• The ancestors of today’s common mole-rats
probably resembled African rock rats.
Structural adaptations arise over time
• Some ancestral rats may have avoided predators better
than others because of variations such as the size of
teeth and claws.
Structural adaptations arise over time
• Ancestral rats that
survived passed their
variations to offspring.
• After many generations,
most of the population’s
individuals would have
these adaptations.
Structural adaptations arise over time
• Over time, natural selection produced modern
mole-rats.
• Their blindness may have
evolved because vision
had no survival advantage
for them.
Other structural adaptations
• Mimicry is a structural adaptation that enables one
species to resemble another species
opossum plays possum well
This fence lizard has
adapted to mimic tree
trunk color
Caterpillar mimics
Bird droppings
In one form of mimicry, a harmless species
has adaptations that result in a physical
resemblance to a harmful species.
The tasty Viceroy Butterfly (left),
Mimics the bitter tasting Monarch on
The Right
Caterpillar mimics a viper
In both looks & movement
Structural adaptations arise over time
• In another form of mimicry, two
or more harmful species
resemble each other.
• For example, yellow jacket
hornets, honeybees, and many
other species of wasps all
have harmful stings and
similar coloration and
behavior.
Animals use Camouflage
• Camouflage allows
animals to blend with
their surroundings
Tartan Hawkfish – blends with
Bright gorgonian fans
A narrow-headed frog native to
Madagascar, blends with the mud &
Tree trunks in its environment
Fossil Evidence
Fossils are important in Evolution
Because they provide a record
Of early life and history
Other Evidence
Anatomy
Homologous Structures: Similar Analogous Structures: Similar
In arrangement, function or in both body parts in function w/ no
evolutionary origin
Vestigial Structure: A body structure in a present day organism
That no longer serves its original purpose, but was useful to
An ancestor
Section 2
Natural Selection
• There are three different types of natural
selection that act on variation:
• 1. Stabilizing
• 2. Directional
• 3. Disruptive
• Stabilizing selection is a natural selection that
favors average individuals in a population.
Selection for
average size
spiders
Normal
variation
Natural selection acts on variations
• Directional selection occurs when natural
selection favors one of the extreme
variations of a trait.
Normal
variation
Selection
for longer
beaks
Natural Selection on Variations
• In disruptive selection, individuals with
either extreme of a trait’s variation are
selected for
The Effects Of Natural Selection
• Natural selection can significantly alter
the genetic equilibrium of a population’s
gene pool over time
• Significant changes in the gene pool
could lead to the evolution of a new
species over time
Speciation
• The evolution of new
species, a process
called speciation
occurs when members
of similar populations
no longer interbreed to
produce fertile
offspring within their
natural environment.
Geographic Isolation
• Geographic isolation
occurs whenever a
physical barrier
divides a population
Isolated habitat
fragments are similar to
islands in the way in
which the species living
there are effected.
Gradualism
• Gradualism is the
idea that species
originate through a
gradual change of
adaptations
Adaptation Radiation
Hawaiian
honeycreepers
When an ancestral
species evolves into an
array of species to fit a
number of diverse
habitats, the result is
called adaptive
radiation
13 Species of Darwins Finches
Differences:
structures of their
beak-adaptation for
cactus eaters, seed
eaters, insect eaters…
Darwin’s
finches of
the
Galapagos
Divergent Radiation
• Adaptive radiation is a
type of divergent
evolution, the pattern
of evolution in which
species that were once
similar to an ancestral
species diverge, or
become increasingly
distinct
Diversity in new environments
Extinct
mamo
Amakihi
Crested
honeycreeper
Kauai
Niihau
Molokai
Oahu
Maui
Lanai
Akialoa
Kahoolawe
Akepa
Akiapolaau
Possible Akikiki
Ancestral
Lasan finch
Liwi
Hawaii
Apapane
Maui
parrotbill
Palila
Ou
Grosbeak
finch
Diversity in a New Environment
• Divergent evolution occurs when
populations change as they adapt to
different environmental conditions,
eventually resulting in new species.
Convergent Evolution
• A pattern of evolution in which distantly
related organisms evolve similar traits is
called convergent evolution
Migration
• Seasonal movements to an area for breeding
•Birds
Fly south for
The winter