Download Honors Evolution Power Point

Evolution
Genetic change in population or
species over generations.
Look at us now!!!
• Put some clothes on!
Theories of Evolution
• I. Lamarck’s Explanation:
– French scientist (1744-1829)
– Proposed that similar species descended
from a common ancestor (fossil records)
– He hypothesized that acquired traits were
passed on to offspring.
Acquired Trait
• It’s not determined by genes!
• Instead, it arises during an organism’s
lifetime as a result of the organism’s
experience or behavior.
– Ex: 1. webbed foot on water birds resulted
from repeated stretching of the membrane
between the toes
–
2. tails – if you don’t use it you loose it!
Thomas Malthus
– Said, “much of human suffering – disease,
famine, homelessness and war was the
inescapable consequence of the human
populations potential to grow much faster than
the rate at which supplies of food and other
resources could be produced
– Resources couldn’t keep up with the increase
in population this kept the population number
down.
What were some of Darwin’s
observations…
• 1. OVER PRODUCTION OF OFFSPRING
all species tend to produce excessive
numbers of offspring
• 2. HERITABLE VARIATIONS –
individuals of a population vary extensively
in their characteristics and that many are
inherited
• 3. LIMITED NATURAL RESOURCES –
environmental resources are limited
EVOLUTION and NATURAL
SELECTION is NOT the same thing!!
• Evolution = genetic change
• Natural Selection = over production,
limited natural resources and heritable
variation influence a gradual change in the
population!!
Charles Lyell (Scottish Geologist)
• Darwin was strongly influenced by his book
Principles of Geology
• Gradual forces gradually change Earth’s
surface and these forces are still operating today.
• Because of Lyell, Darwin believed that slow
natural processes such as growth of mountains
due t o earthquakes could account for the
presence of marine fossils on the top of
mountains!
• Natural catastrophes very important in evolution
Last one!
• Alfred Wallace:
– Had theory IDENTICAL to Darwin!
– Caused Darwin to publish “Origin of Species”
by means of natural selection!!!
Beginning of Modern Evolutionary
Theory
• II. Charles Darwin (1809-1882) & Alfred
Wallace (1823-1913)
– “natural selection”-hypothesis that
organisms best suited to their environment
reproduced more successfully than other
organisms
– Darwin & Wallace announced their
hypotheses at the same time
– Darwin’s name became more associated with
evolution The Origin of Species published
Darwin’s Voyage on the Beagle
• Sailed in 1831 for five years
• Collected specimens and kept careful
records of his observations
• Sailed to South America (Galapagos
Islands) and the South Pacific
Darwin’s Findings
• 1. returned to England in October 1836
• 2. collected 13 similar but separate
species of finches.
• 3. Each finch species had a distinctive
bill for specialized food source.
• Implied that the finches shared a recent
common ancestor
Darwin’s Finches
Darwin’s Findings
A GRUB!!!!!!!
• !
Darwin’s Theories
• TWO THEORIES;
– 1. DESCENT WITH MODIFICATION – The
newer forms appearing in the fossil record are
actually the modified descendants of older
species
• Organisms similar to each other come from a
recent common ancestor, organisms that are
more dissimilar such as finches and armadillos
share a more remote ancestor
Continue…
• 2. MODIFICATION BY NATURAL
SELECTION – states HOW evolution
occurs.
– Organisms having traits that make them
better suited for survival tend to leave more
offspring than organisms with fewer beneficial
traits. Darwin called the different degrees of
successful reproduction among organisms in
a population NATURAL SELECTION
Evidence to support Darwin’s
theory:
• Biogeography – the geographic
distribution of species, first suggested to
Darwin that organisms evolve from
common ancestors
• Comparative Anatomy – the study of the
body structures in different organisms,
anatomical similarities gives evidence of a
common ancestor
Continue…
• Homologous structures – structures that
are similar in different species of common
ancestry but have different functions
• Comparative embryology – closely
related organisms often have similar
stages in their embryonic development
• Fossils – imprints or remnants of
organisms that lived in the past
Biogeography
• Biogeography – is the study of the
geographical distribution of fossils and of
living organisms.
– A comparison of recently formed fossil types
with types of living organisms in the same
geographic area shows that new organisms
arise in areas where similar forms already
lived.
• Ex: armadillos in North & South America where
glyptodonts lived in the past.
Armadillos
Glyptodonts
Evidence of Evolution
• 1. HOMOLOGOUS STRUCTURES:
similar features that originated in a shared
ancestor
– Similar in structure BUT differ in function!!
– Ex: penguin, bat, alligator, & human (all
derive from the same embryological
structures)
– These examples i.e. share a fairly recent
common ancestor
Homologous Structures
Continue…
• 2. ANALOGOUS STRUCTURES: Similar
functions BUT differ in structure and
embryological development
– Ex: wings of a hummingbird and humming
moth – both can hover to feed
Analogous Structures
Continue…
• 3. Vestigial Structure: Features that
were useful to an ancestor, but they are
not useful to the modern organism that has
them.
– Ex: tailbone in humans, appendix, some
snakes have tiny pelvic bones and limb
bones, some whales have pelvic bones
along with four chambered stomach like a
cow!
Vestigial Structures
Continue…
• 4. Similarities in Embryology
– Ex: all
vertebrate embryos are
similar, but those similarities fade
as development proceeds –
evidence that indicates that
vertebrates share a common
ancestor
Vertebrate Embryos
Continue…
• 5. Similarities in Macromolecules: The
more similar homologous proteins are in
different species, the more closely related
the species are thought to be.
– Ex: the amino acid sequence in human
hemoglobin and gorilla hemoglobin differ
by ONE amino acid
– While the Hb of humans and frogs differ by
67 amino acids!!
What’s natural selection?
• A mechanism of evolution that allows for
differential (unequal) success in
reproduction
• Examples:
– Finches – dry years  large beaks (stronger)
– Finches – wet years  small beaks
– Insecticides  evol. Of hundreds of species
WAIT!!!!!
What do you think of this??
• Oh boy!
Let’s sum it up!
• SURVIVAL OF THE FITTEST!
– Those whose characteristics adapt them best
to the environment are most likely to survive
and reproduce!!
– Favored traits will be seen more and more
while unfavored ones will be seen less and
less in ensuing generations
– EVOLUTION IS MEASURED IN A
POPULATION NOT IN ONE INDIVIDUAL!
Patterns of Evolution
• 1. Coevolution: the change of two or
more species in close association with
each other is called coevolution
– Predators and their prey sometimes co-evolve
• Ex: “tropical region” bats feed on nectar
– Bats have slender muzzle and long tongue that help
them to feed,flowers are light in color which helps bats to
see them at night and have a fruity odor that is attractive
to the bats.
Tropical Bats!
Baby Bats!!
CLOSE UP!!!!
• COOL!
Flowers with Nectar!
Continue…
• 2. Convergent Evolution: occurs when
the environment selects similar
phenotypes, even though the ancestral
types were quite different from each other.
– Analogous structures, such as similar fins in
very different animals, are associated with
convergent evolution
• Ex: sharks and porpoises
Porpoises
Sharks
Continue…
• 3. Divergent Evolution: two or more
related populations or species become
more and more dissimilar. Divergence is
nearly always a response to differing
habitats and can result in new species
– A) adaptive radiation: many related species
evolve from a single ancestral species ex:
Galapagos finches
– B) artificial selection: all domestic dogs are
the same species “Canis familiaris”
Darwin’s ideas are supported by
ARTIFICIAL SELECTION
• Artificial Selection
– The selective breeding of desired traits that in
fact modify species. Whoa nelly!!!
• Ex. Domestic dogs, cats, and plants
– Broccoli, caulif., cabbage, brussel sprouts,
Canis familiaris
• !
So Darwin reasoned that if..
• So much change could be achieved in a
relatively short period of time by artificial
selection, then over millions of years and
hundreds of thousands of generations,
natural selection should be able to modify
species considerable.
– YEAH BOY, UH-HUH
POPULATION GENETICS
• Populations  a group of individuals of
the same species, living in the same place
at the same time
• Populations are the smallest unit that can
evolve.
How can we measure evolution?
• As a change in the prevalence of certain
traits in a population over several
generations
Individuals of a population do NOT
evolve
• AGAIN…
• Natural selection acts on individuals-their
char. Affect their chances of survival and
reproduction.
• Evolution is only apparent when a
population is tracked over time
Darwin understood evol., but didn’t
understand the genetic basis of a
population change…
• Today we know:
– Spontaneous mutations may produce new
traits
– Segregation & indep. Assort. Produce
variations in gametes & thus in offspring
– Genes are passed through gametes from
parents to offspring
MODERN SYNTHESIS
• Theory developed in the 1940’s
• Includes genetics and evolution!!
• POPULATIONS ARE THE UNITS OF
EVOLUTION BASED ON NATURAL
SELECTION
CONTINUE..
• Modern synthesis deals with THE
RELATIONSHIP BETWEEN
POPULATIONS AND SPECIES
• SPECIES=group of organisms that
can reproduce fertile offspring!
Where the species live matters!
• Species distributed over a
geographic range –> have
different gene pool
• THAN
• Species localized  due to water,
islands, mountains etc.!!!
Studying evolution at the
population level scientist
focus on the GENE POOL
• GENE POOL IS THE SUM OF
THE GENES IN A POLULATION!
• (It’s where all members of the
next generation get their genes!)
MICROEVOLUTION
• When allele frequencies in a
population change over
generations, this is evolution at its
smallest scale.
• (genes are represented by
alleles) Ex: gene for the
color of your eyes has many
alleles – B,b)….
Let’s Review!
• 1. What is a GENE POOL?
–Sum of genes in a population
that will be passed on!!
What is microevolution?
• when allele frequency in
a population change over
generations this is
evolution at its
scale.
SMALLEST
Remember!
• Sexual reproduction on its
own does NOT cause
microevolution
• Other agents must also act
on the population!
(environment)
There are several potential
cause of microevolution:
• 1.
• •
• 2.
• 3.
Genetic Drift:
a) bottleneck effect
- founder effect
Gene Flow
Mutation
Genetic Drift
• A change in the gene
pool of a small
population due to
chance!
Genetic Drift
Ex: Northern Elephant Seal (extinct)
The Bottleneck Effect
• Genetic drift resulting
from an event that
drastically reduces
population size! Ex:
hunting to the point of
extinction!
The Bottleneck Effect
• *
Bottleneck Effect
• !
The Founder Effect
•Genetic drift that results from
the colonization of a new
location by a small number
of individuals – small size, less
representative of the gene pool.
Founder Effect
• Ex: Amish residents of Lancaster County,
PA – Ellis-van Creveld Syndrome
Genetic Drift & Founder Effect
• Symptoms: short arms & legs, extra fingers, &
in some cases heart defects.
Gene flow
•When fertile individuals
move into or out of a population
or when gametes are
transferred between
populations.
Gene Flow
• *
Gene flow
• *
Mutations
•A random change
in an organism’s
DNA that may
create a new allele.
mutation
• HUH??
HARDY-WEINBERG
EQUILIBRIUM
• Allele frequency with
ONLY sexual
reproduction involved!
• NO OUTSIDE AGENTS
VARIABLES
p = dominant
q = recessive
2pq = heterozygous
p+q=1
2
2
p + 2pq + q = 1
5 Conditions are required for
Hardy-Weinberg Equilibrium
• 1. no mutations
• 2. no migration
• 3. very large population
size
Continue…
• 4. random mating
• 5. NO NATURAL
SELECTION OCCURS!
Hardy-Weinberg Equillibrium
• Conditions rarely met by a natural
population
• Gives us a basis to compare
nonevolving population vs. actual
ones with gene pools that are
changing!
Patterns of Selection
• Stabilizing Selection or Balancing
Selection
• Disruptive Selection or Diversifying
Selection
• Directional Selection
Stabilizing Selection
• Stabilizing selection is a type of natural
selection that favors the average
individuals in a population. This process
selects against the extreme phenotypes
and instead favors the majority of the
population that is well adapted to the
environment. Stabilizing selection is often
shown on a graph as a modified bell curve
that is narrower and taller than the norm.
Stabilizing Curve
Disruptive Selection
• Disruptive selection is a type of natural
selection that selects against the average
individual in a population. The make up of
this type of population would show
phenotypes of both extremes, but have
very few individuals in the middle.
Disruptive selection is the rarest of the
three types of natural selection.
Directional Selection
• Directional selection is a type of natural
selection that favors one extreme
phenotype over the mean or other
extreme. This phenomena is usually seen
in environments that have changed over
time. Changes in weather, climate, or food
availability lead to directional selection.