Evolution PowerPointx

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Transcript Evolution PowerPointx

Just how do species change over time????
Early atmosphere, evidence, natural selection
and disease agents influence natural
● Evolution “ simple” definition: change over
● Evolution helps us to understand the history
of life.
The central idea of biological evolution is that all
life on Earth shares a common ancestor, just as
you and your cousins share a common
Fossil Record
Comparative Anatomy
Embryological Development
DNA Similarities
All organisms have adaptations which help
them survive in their particular environment
Adaptation: a structure or behavior that helps
an organism better survive in its environment
Examples: Mimicry, camouflage and
Mimicry: a structural adaptation that
enables one species to resemble another
◦ E.g. A harmless species might mimic a poisonous
Camouflage: a structural adaptation that
allows a species to blend in with its
Many bacteria have evolved resistance to
antibiotics in the last 50 years
Pests have evolved resistance to pesticides
Organisms with stronger immune systems are
more likely to survive pathogens.
Eventually, the species that builds up
antibodies for this particular pathogen will
The bacteria that build up a resistance the
antibiotics survive.
The ones that do not also die, just like in
animals and plants.
Evolution by natural selection happens in
populations, not individuals. A single
organism cannot evolve. Populations evolve.
Populations evolve because there is variation
Variation causes some organisms to be better
fit than others. These better fit organisms
are more likely to survive and pass their
genes to the next generation
Evolution is the gradual change in a population
over time
Darwin was the first scientist to realize that
evolution can work by natural selection.
◦ Natural Selection – Organisms with traits well suited
to an environment are more likely to survive and
produce more offspring than organisms without
these favorable traits
 “Survival of the fittest”
 E.g. Thicker fur is a favorable trait in cold
English naturalist who proposed the theory of
evolution by natural selection
Darwin sailed around the world on the HMS
Beagle and carefully studied thousands of
different plants and animals
On the Galapagos Islands Darwin found very
strange plants and animals that don’t exist
anywhere else in the world!
Different islands have different types of
finches not found on any other islands.
Convergent evolution: distantly related
organisms evolve to become more similar
◦ Happens when unrelated species adapt to similar
environments, possibly in different parts of the
Divergent evolution: species that once were
similar become increasingly different
◦ Happens when populations adapt to different
There are 3 basic types of natural selection
◦ Directional Selection
◦ Stabilizing Selection
◦ Disruptive Selection
Directional selection: favors one of the
extreme variations of a trait
◦ E.g. Male peacock tail feathers: Females favor
larger tail feathers. Therefore males with larger
feathers reproduced more often. Over many
generations tail feathers grow larger and larger
Stabilizing selection: favors average
individuals in a population
◦ E.g. Human infants: Too small = bad; too large =
bad; average = good
Disruptive selection: favors individuals with
either extreme of a trait but intermediate
individuals have a disadvantage
◦ E.g. Cuddlefish (a type of squid): Being large is an
advantage because females prefer larger males.
Being small is an advantage also. Small males
impersonate females trick the females into mating.
● Atmosphere contained all of the following
Carbon Dioxide
● No oxygen….oxygen came later with
Experiment conducted by Miller and Urey
proposed simple- organic molecules could have been
synthesized in the atmosphere of early Earth and
rained down into the oceans.
Fossil: Any trace of a dead organism
◦ Fossils show the evolution of species over the past
millions of years
◦ Fossil evidence proves that modern species have
evolved from ancient species
Puijila the walking seal
Homologous structures: Body structures on
different organisms that are similar in
structure (same bones) and evolved from a
common ancestor
Homologous Structures
Analogous structures: Body structures on
different organisms that are similar in
function but did not evolve from the same
ancestor (bird wing and butterfly wing)
Moth (insect)
Pterodactyl (reptile)
Bat (mammal)
Analogous Wing Structures
Vestigial structure: body structure in an
organism that no longer serves its original
purpose but was useful to an ancestor
(useless wings on the African ostrich)
Early in development, human embryos and
embryos of all other vertebrates are very
similar, which suggests that all vertebrates
are related
Nearly all organisms have DNA, ATP, and
many of the same proteins and enzymes
The DNA (genes) of closely related organisms
looks very similar
Genetic Drift
Gene Flow
Natural Selection
Gene pool: collectively, all of the alleles of the
population’s genes
Allelic frequency: the percentage of any
specific allele in the gene pool
Genes can enter and leave a population’s
gene pool for many reasons
Populations in which the gene pool is not
changing are said to be in genetic equilibrium
New genes can be added to the population by
errors in DNA copying called mutations
Most mutations are neutral or bad!
Very very rarely a mutation might come along
that improves an organism’s chance at
survival or reproduction
These mutant genes will be passed along to
offspring and become more common in the
gene pool over time
If the mutation offers a large advantage,
eventually (after many generations) all
members of the population will have the
beneficial mutation
◦ Artificial Selection: Humans choose
individuals with certain traits for breeding
◦ After many generations of selection,
dramatic evolutionary changes can result
 Dogs
 Fruits/Vegetables
 Livestock
Gene flow: the transport of genes by traveling
◦ When an individual leaves a population, its genes
are lost from the gene pool
◦ When an individual enters a population, its genes
are added to the gene pool
Genetic drift: when allelic frequencies are
changed by random events in a isolated
◦ Example: diseases, natural disasters, mating habits
A certain population may become isolated
and evolve to fit new or different
environmental conditions
The isolated population may change so much
that it can no longer mate with the original
◦ Similar to the evolution of new languages
There are several reasons why similar
populations no longer breed, creating new
◦ Geographic Isolation
◦ Reproductive Isolation
North rim of Grand
South rim of Grand
Gradualism: idea that species originate through a
gradual change of adaptations (longer than
10,000 years)
◦ E.g. Fossil evidence shows that sea lilies evolved slowly
and steadily over time
Punctuated equilibrium: idea that species
originate in rapid bursts (10,000 years or less)
with long periods of genetic equilibrium in
◦ Global ice age causes rapid adaptation of thick fur
Both gradualism and punctuated equilibrium are
known to occur