darwin and natural selection

1. Darwin and Natural Selection
Darwin and Natural Selection
 Was from England.
Was from England.
 Beagle Expedition: found
Beagle Expedition: found
unique species that looked
unique species that looked
similar to species from other
similar to species from other
parts of the world.
parts of the world.
 Found that many of the
Found that many of the
plants and animals on
plants and animals on
Galapagos resembled those
Galapagos resembled those
in nearby South America
in nearby South America

2. Voyage of the HMS Beagle
Voyage of the HMS Beagle

3. The Origin of the Species
The Origin of the Species
 On The Origin of Species
On The Origin of Species
by Means of Natural
by Means of Natural
Selection
Selection Nov. 1859
Nov. 1859
Charles Darwin
Charles Darwin
 Darwin suggested that
Darwin suggested that
humans are related to
humans are related to
apes
apes

4. Other scientist
Other scientist

Lamarck believed that over the lifetime of an
Lamarck believed that over the lifetime of an
individual, physical features increase in size
individual, physical features increase in size
because of use and decrease from nonuse
because of use and decrease from nonuse

Malthus suggested that human pops. do not
Malthus suggested that human pops. do not
grow unchecked because death caused by
grow unchecked because death caused by
disease, war, and famine slows growth
disease, war, and famine slows growth

5. Natural Selection
Natural Selection
 Natural selection: organisms with favorable
Natural selection: organisms with favorable
traits for a particular environment survive,
traits for a particular environment survive,
reproduce, and pass these traits on to the
reproduce, and pass these traits on to the
next generation (those with less favorable
next generation (those with less favorable
traits are less likely to survive).
traits are less likely to survive).
 Adaptation- inherited trait that has become
Adaptation- inherited trait that has become
common in a population because the trait
common in a population because the trait
provides a selective advantage
provides a selective advantage

6. Evolution of Humans
Evolution of Humans
 The Descent of Man,
The Descent of Man,
and Selection in
and Selection in
Relation to Sex
Relation to Sex
Charles Darwin 1871
Charles Darwin 1871
 Darwin outlined
Darwin outlined
sexual selection to
sexual selection to
explain the evolution
explain the evolution
of humans
of humans

7. 4 Tenets of Natural
4 Tenets of Natural
Selection
Selection
 All populations have genetic variation.
All populations have genetic variation.
 The environment presents challenges to
The environment presents challenges to
successful reproduction.
successful reproduction.
 Individuals tend to produce more offspring
Individuals tend to produce more offspring
than the environment can support.
than the environment can support.
 Individuals that are better fit their
Individuals that are better fit their
environment tend to live longer, reproduce
environment tend to live longer, reproduce
more, and spread their genes throughout the
more, and spread their genes throughout the
population.
population.

8. Darwin’s 4 Facts
Darwin’s 4 Facts
 Exponential Growth of Populations
Exponential Growth of Populations
 Factors will prevent Exponential
Factors will prevent Exponential
Growth(Steady State)
Growth(Steady State)
 Variability among species
Variability among species
 Traits are inheritable
Traits are inheritable

9. Darwin’s 2 Inferences
Darwin’s 2 Inferences
 Competition for resources
Competition for resources
 Individuals most fit for their environment
Individuals most fit for their environment
will survive.
will survive.

10. Sources of Genetic Variation
Sources of Genetic Variation
 Mutation/ Translocation- Mutation slowly
Mutation/ Translocation- Mutation slowly
introduces new alleles which natural selection
introduces new alleles which natural selection
helps distribute (can be harmful, beneficial or
helps distribute (can be harmful, beneficial or
have no significance)
have no significance)
 Crossing Over- exchange of homologous
Crossing Over- exchange of homologous
chromosome segments
chromosome segments
 Independent Assortment- assortment of
Independent Assortment- assortment of
chromosomes
chromosomes
 Sexual Reproduction- combination of allelles of
Sexual Reproduction- combination of allelles of
two individuals
two individuals
 Immigration- incoming allelles to a gene pool
Immigration- incoming allelles to a gene pool

11. Mechanisms for Evolutionary
Mechanisms for Evolutionary
Change
Change
 Natural Selection
Natural Selection

12. Population Genetics and
Population Genetics and
Evolution
Evolution
 Populations evolve when natural selection causes changes
Populations evolve when natural selection causes changes
in their allele distribution.
in their allele distribution.
 Natural selection causes the greatest changes to
Natural selection causes the greatest changes to
populations’ gene pools, but is not the only cause
populations’ gene pools, but is not the only cause
of change
of change
 Gene Pool- all the alleles of a population of a species
Gene Pool- all the alleles of a population of a species

In a population’s gene pool, each allele has a certain
In a population’s gene pool, each allele has a certain
frequency which governs the frequency of phenotypes
frequency which governs the frequency of phenotypes

If a population’s allele frequencies do not change, it is not
If a population’s allele frequencies do not change, it is not
evolving and is said to be in genetic equilibrium
evolving and is said to be in genetic equilibrium
 Individuals don’t evolve, populations of species do!
Individuals don’t evolve, populations of species do!

13. Other Influences on the Gene
Other Influences on the Gene
Pool
Pool
 In
In small
small populations, change events
populations, change events
(crossing over, translation errors) can
(crossing over, translation errors) can
cause shifts in a gene pool = genetic drift
cause shifts in a gene pool = genetic drift
 Individuals may move into or out of a
Individuals may move into or out of a
population, bringing or taking alleles with
population, bringing or taking alleles with
them = migration
them = migration

14. Population Evolution
Population Evolution
 Gene flow-the movement of genes into or
Gene flow-the movement of genes into or
out of a population due to interbreeding.
out of a population due to interbreeding.

Immigration- the flow of alleles into a
Immigration- the flow of alleles into a
population.
population.

Emigration-the flow of alleles out of a
Emigration-the flow of alleles out of a
population.
population.
 Genetic drift- the random change of allele
Genetic drift- the random change of allele
frequency in a population, not due to natural
frequency in a population, not due to natural
selection.
selection.

15. Population Evolution
Population Evolution
 Artificial selection- a process in which humans
Artificial selection- a process in which humans
consciously select for or against particular features
consciously select for or against particular features
in organisms.
in organisms.
 Genetic bottleneck-an event in which the
Genetic bottleneck-an event in which the
populations’ size is greatly reduced; reduces
populations’ size is greatly reduced; reduces
genetic variability
genetic variability
 Founder effect-changes in gene frequency from
Founder effect-changes in gene frequency from
starting a new population from a small number of
starting a new population from a small number of
individuals; reduces genetic variability.
individuals; reduces genetic variability.

16. Adaptations
Adaptations
 Structural:
Structural:

Can change the size and/or shape of a body part
Can change the size and/or shape of a body part

For example: thorns, wings, mimicry (copy the appearance
For example: thorns, wings, mimicry (copy the appearance
of another species), camouflage (blend in with environment)
of another species), camouflage (blend in with environment)

Change within a population over time (anywhere from 100
Change within a population over time (anywhere from 100
years to millions of years) depending on type of adaptation,
years to millions of years) depending on type of adaptation,
rate of reproduction and environmental factors
rate of reproduction and environmental factors
 Physiological
Physiological

Help populations overcome chemicals they encounter
Help populations overcome chemicals they encounter
(antibiotics, pesticides, herbicides, etc)
(antibiotics, pesticides, herbicides, etc)

Develop rapidly (example: bacterial resistance to penicillin)
Develop rapidly (example: bacterial resistance to penicillin)

17. Evidence for Evolution
Evidence for Evolution
 Fossils
Fossils
 Anatomical relationships
Anatomical relationships
 Embryological development
Embryological development
 Genetic comparisons
Genetic comparisons

18. Fossils
Fossils
 Fossils can help provide a record for life
Fossils can help provide a record for life
 However, the fossil record is incomplete -
However, the fossil record is incomplete -
there are large gaps - therefore each and
there are large gaps - therefore each and
every step of evolution can not be followed
every step of evolution can not be followed
 Scientists need to find intermediate
Scientists need to find intermediate
species - and once they do, they can
species - and once they do, they can
provide us with a step by step sequence of
provide us with a step by step sequence of
evolution
evolution

19. Anatomical Comparisons
Anatomical Comparisons
 Homologous structures
Homologous structures

Same form, different use
Same form, different use

Indication of common evolutionary ancestor
Indication of common evolutionary ancestor
 Vestigial structures
Vestigial structures

Evolutionary remnants of structures that were
Evolutionary remnants of structures that were
important in a past ancestor
important in a past ancestor

20. Embryological Development
Embryological Development
 There are noted similarities between the
There are noted similarities between the
embryological development of all
embryological development of all
vertebrates (fish, chicken, rabbit, human,
vertebrates (fish, chicken, rabbit, human,
etc)
etc)

Presence of gills and tails in all supports
Presence of gills and tails in all supports
evidence that gill-breathing vertebrates
evidence that gill-breathing vertebrates
preceded air-breathing, terrestrial species
preceded air-breathing, terrestrial species

21. Genetic Comparisons
Genetic Comparisons
 All living things use DNA.
All living things use DNA.
 All living things use the same genetic code.
All living things use the same genetic code.
 Can show relationships between species
Can show relationships between species
(human and chimpanzee DNA are 99%
(human and chimpanzee DNA are 99%
identical and are closer than chimpanzees
identical and are closer than chimpanzees
are to apes)
are to apes)
 Can help reveal when species diverged
Can help reveal when species diverged
from their ancestral types
from their ancestral types

22. Types of Natural Selection
Types of Natural Selection
 Stabilizing Selection - favors average traits
Stabilizing Selection - favors average traits
(average sized spiders fair better than
(average sized spiders fair better than
both large and small)
both large and small)
 Directional Selection - favors one extreme
Directional Selection - favors one extreme
of a trait (the longer the beak the better)
of a trait (the longer the beak the better)
 Disruptive Selection - favors both
Disruptive Selection - favors both
extremes of a trait (intermediate at
extremes of a trait (intermediate at
disadvantage - often eliminated)
disadvantage - often eliminated)

23. Evolution of a Species =
Evolution of a Species =
Speciation
Speciation
 Species = group of organisms that look
Species = group of organisms that look
alike and have the ability to interbreed and
alike and have the ability to interbreed and
produce fertile offspring in nature
produce fertile offspring in nature
 Speciation occurs when
Speciation occurs when

Interbreeding is prevented
Interbreeding is prevented

Production of fertile offspring is prevented
Production of fertile offspring is prevented

24. Causes of Speciation
Causes of Speciation
 Isolation of populations
Isolation of populations - Two populations of the
- Two populations of the
same species do not mate because of some
same species do not mate because of some
form of separation
form of separation

If populations can’t interbreed due to isolation, their
If populations can’t interbreed due to isolation, their
allele frequencies can become more and more
allele frequencies can become more and more
different from each other
different from each other

Each population will adapt to its environment,
Each population will adapt to its environment,
eventually preventing breeding with members of
eventually preventing breeding with members of
other populations (reproductive isolation)
other populations (reproductive isolation)
 Changes in chromosome number causes
Changes in chromosome number causes
instantaneous speciation
instantaneous speciation
 Most speciation happens gradually
Most speciation happens gradually

25. Types of Isolation
Types of Isolation
 Geographic- geographic barriers form that
Geographic- geographic barriers form that
separate two populations.
separate two populations.
 Ecological- different environmental factors
Ecological- different environmental factors
may cause isolation (wet vs. dry, soil
may cause isolation (wet vs. dry, soil
conditions, etc.)
conditions, etc.)
 Reproductive- mating structures and
Reproductive- mating structures and
behaviors may isolate two populations
behaviors may isolate two populations
 Temporal- two populations may reproduce at
Temporal- two populations may reproduce at
different times
different times

26. Types of Evolution
Types of Evolution
 Divergence (ex: adaptive radiation);
Divergence (ex: adaptive radiation);

Single populations splits to adapt to different
Single populations splits to adapt to different
environments
environments
 Convergence
Convergence

Unrelated species become similar as they
Unrelated species become similar as they
adapt to a similar environment.
adapt to a similar environment.

Analogous structures
Analogous structures
• Same use, different form
Same use, different form
• Not evidence of a common evolutionary
Not evidence of a common evolutionary
ancestor
ancestor

27. Rate of Speciation
Rate of Speciation
 Fossil record suggests the rate is variable
Fossil record suggests the rate is variable

Gradualism: slow, steady process of
Gradualism: slow, steady process of
change
change

Punctuated equilibrium: long periods of
Punctuated equilibrium: long periods of
genetic stability punctuated by rapid
genetic stability punctuated by rapid
changes to new environmental
changes to new environmental
conditions
conditions

28. Pace of Evolution
Pace of Evolution
 Gradualism- the pace of natural selection
Gradualism- the pace of natural selection
is gradual change.
is gradual change.
 Punctuated Equilibrium- model of
Punctuated Equilibrium- model of
evolutions that states there are differing
evolutions that states there are differing
periods of rapid change and periods of
periods of rapid change and periods of
little to no change.
little to no change.
 Why? What could cause this?
Why? What could cause this?