Download Biological evolution

Evolution: Process
and Pattern BIOL 333
Dr. Liane Cochran-Stafira
Syllabus - course goals and
policies
What is evolution?
Epigenetics
Evolution
Change through time –
Descent with modification
Biological evolution
Any change in the inherited
traits of a population that
occurs from one generation to
the next
Biological evolution
Any change in gene
frequencies in a population
Evolution is the unifying
theory of the biological
sciences.
Evolutionary Biology aims to
discover the history of life and the
causes of the diversity and
characteristics of organisms.
Darwin’s Evolutionary Theory

Published in The Origin of Species in 1859

Consisted of two major hypotheses:
1.
All organisms have descended, with modification, from common ancestral forms of life.
2.
A chief agent of modification is Natural
Selection.
What is evolution?
 Microevolution
– changes within species
Natural selection
 Other evolutionary forces

 Macroevolution
– changes between species
Case study– HIV evolution
1) Pattern of evolution
- population differs between two points in time
new traits  new problems for infected
individuals
2) Process – HOW has this change happened?
- change in allele frequencies in populations
3) Where did HIV come from?
What is HIV related to?
How did it become a new disease?
Biological Evolution
- genetic change in population through time
HIV+ patient
time 2
time 1
high viral load
begins AZT therapy
lower viral load
continues AZT therapy
time 3
higher viral load
AZT therapy ineffective
What happened?
Has there been evolution??
What has changed?
Has the change been genetic?
What evolution is not

Evolution is not
 Steady

progress to a goal
Evolution does not invent things from scratch
 It
works with what is available
 Ex. Panda’s thumb

Evolution does not
 Produce
optimal adaptations
Common misconceptions about
evolution
Common
Misconceptions 1
Evolution is “just” a theory
Evolution is “just” a theory

Scientific theories backed by multiple lines of
evidence
 Provide
overarching explanation for major
aspects of natural world

Other scientific theories
 Gravity
 Plate
tectonics
 Germ theory

Evolutionary theory overwhelmingly accepted
by scientists
Scientific Theories

Scientific Theory
Powerful, broad explanation of a large
set of observations
Rests on many well-tested hypotheses
Makes predictions
Generates additional hypotheses
CSI, Sherlock Holmes – “I have a
theory about who killed the victim.”
Incorrect! “They have a(n) hypothesis!”
 Note:
Scientific Theories

A scientific theory is an explanation of
a set of related observations based on
well-supported hypotheses from several
different, independent lines of research.

Ex. The germ theory of disease arose
from the accumulated observations of
scientists such as Pasteur and Koch.
Other Biological Theories
Cell Theory
 Bioenergetics
 Homeostasis
 Germ Theory of Disease
 Theory of Genetics – information transfer
 Ecosystem Theory

Common
Misconceptions 2
Evolutionary biologists understand
everything about the history of life
Evolutionary biologists understand
everything about the history of life

Biologists continually discover new
aspects of life
 All
evidence fits within context of evolution
Common
Misconceptions 3
Evolution explains the origin
of life
Evolution explains the origin of
life

Evolution deals with how life has changed
after it originated

Other scientific fields address the origin of life
Common
Misconceptions 4
Evolutionary biologists search
for missing links
Evolutionary biologists search for
missing links

Biologists expect the fossil record to be
incomplete
 Finding

direct ancestors is unlikely
Available evidence strongly supports
relationships between current and past
species
 Relationships
shed light on how traits evolved
Common
Misconceptions 5
Evolution violates the second
law of thermodynamics
Evolution violates the second
law of thermodynamics

Holds that disorder increases in closed
systems
 Earth
is not a closed system
 Sun provides constant input of energy
Common
Misconceptions 6
Evolution is natural selection
Evolution is natural selection
Natural selection is a mechanism of
evolutionary change
 Other mechanisms:

 Genetic
drift
 Sexual selection
Common
Misconceptions 7
Evolution is entirely random
Evolution is entirely random

Evolution includes random and non-random
components
 Mutations
are random
 Natural selection is the non-random spread of
particular mutations

Convergent evolution demonstrates that
evolution is non-random
 Phenotypes
are predictable when
environments are similar
Common
Misconceptions 8
Organisms evolve adaptations
they “need”
Organisms evolve adaptations
they “need”

Evolution cannot identify needs
 Mutations
do not occur because they would
be adaptive in an environment
 If beneficial mutations happen to occur they
may increase in frequency through selection
Common
Misconceptions 9
Evolution is a march of
progress
Evolution is a march of progress

Evolution is not ladder-like
 New
species result from branching events
Common
Misconceptions 10
Evolution always moves from
simple to complex
Evolution always moves from
simple to complex

Evolution can also move from complex to
simple
 Lizards
 snakes
Rodhocetus
Ambulocetus
Basilosaurus
Balaenoptera (blue whale)
Common
Misconceptions 11
Evolution results from
individuals adapting to
environment
Evolution results from individuals
adapting to environment

Evolution only works on inherited traits
 Acquired

changes are not passed to offspring
Populations evolve; individuals do not
 Evolution
results from changes in allele
frequencies
Common
Misconceptions 12
Organisms are perfectly
adapted to their environment
Organisms are perfectly adapted to
their environment

Natural selection can only work with
available variation
 Constrained

by physics and development
Many traits involved in trade-offs
 e.g.
guppy brain size
Adaptive Evolution


Natural selection does not result in a
perfect match between organisms and
their environments, partly because
environments are constantly changing.
Also, there are several constraints on
evolution:
1.
2.
3.
4.
Lack of genetic variation
Evolutionary history
Ecological trade-offs
Physical, developmental constraints mechanical
Adaptive Evolution
1.
Lack of genetic variation: If there is no
beneficial allele, adaptive evolution at
that gene can not occur.



Example: Initially, a mosquito population lacked
alleles that provided resistance to pesticides, so the
pesticides were effective.
Advantageous alleles arise by chance, not “on
demand.”
Resistance gene arose by random mutation.
Pesticides were ineffective against mosquitoes that
carried the mutation.
Adaptive Evolution
2.
Evolutionary history: Natural selection
works on the traits already existing in
organisms.

Organisms have certain characteristics and
lack others because of their ancestry.
 Example: Dolphins evolved from terrestrial
mammals; they have lungs and cannot
“breathe” underwater.
Adaptive Evolution

Natural selection can bring about great
changes, such as the mode of life and
streamlined body form of the dolphin.

But it does so by modifying traits that are
already present, not by creating
advantageous traits de novo.
Evolution takes the easy way out
Panda’s thumb:
Co-opt a ready-made structure
for another use; may not be
“best” solution, but it works and
didn’t take a lot of new
developments
Physical laws can constrain
evolution of trait
Limit size (large and small)
Adaptive Evolution
3.
Ecological trade-offs: All organisms face
trade-offs in allocation of energy and
resources to growth, reproduction, and
survival.

Adaptations represent compromises in the
abilities of organisms to perform different
and sometimes conflicting functions.
Adaptive Evolution
4.
Physical constraints: mechanical
problems. Physical laws can constrain
evolution of trait

Limit to size (large and small). Ex. Limit to
size of arthropods because exoskeleton
would become too heavy to support since
muscles are all attached to it.
Common
Misconceptions 13
Evolution happens for the
good of the species
Evolution happens for the good of
the species

Evolution selects traits that are beneficial
for individuals or their genes
 Traits
that are bad for individuals (or genes)
will not be selected even if they are good for
the species
Common
Misconceptions 14
Evolution promotes
selfishness and cruelty
Evolution promotes selfishness and
cruelty

Natural selection favors traits that increase
reproductive success
 Different
conditions select for different traits
 Cooperative traits are beneficial under some
conditions
Common
Misconceptions 15
Evolution seeks peaceful
harmony in nature
Evolution seeks peaceful harmony
in nature

Natural selection favors traits that increase
reproductive success
 Can
result in exploitation
Common
Misconceptions 16
Life can be divided into higher
and lower forms
Life can be divided into higher and
lower forms

All of life is adapted to the environment in
numerous ways
 Environments
differ so adaptations differ
 One adaptation is not “superior” to another
adaptation
All organisms are connected by the
passage of genes along the branches
of the phylogenetic Tree of Life.
Common
Misconceptions 17
Evolution has produced a
stable diversity of life
Evolution has produced a stable
diversity of life

Extinction means diversity is
not stable
 99%
of all species that ever
existed are extinct