Transcript Evolution - juan

The Origin and Evolutionary History
of Life
Conditions on Early Earth
◦ Age of Earth ~4.6 billion years
◦ Atmosphere had free
 No O2
 Rich in CO2, H2O, CO, H2, N2
 Also ammonia (NH3), sulfuric acid
(H2S), methane gas (CH4)
◦ Presence of oxygen (photosynthesis)
◦ Increased sun energy
◦ Formation of organic compounds
◦ Sufficient time
Protobionts appeared first. They are
considered to have possibly been the
precursors to prokaryotic cells.
 Then appeared heterotrophic bacteria that
fed on organic molecules & carried anaerobic
fermentation
Protobiont
Heterotrophic Bacteria

Cyanobacteria split water molecules and
released oxygen through photosynthesis.
 This bacteria accounts for much of the
oxygen in our atmosphere.

Endosymbiontic Theory
 Mitochondria and chloroplasts derived
from prokaryotes
 A prokaryote ingested but not digested,
some aerobic bacteria
 Over along time the aerobe became
mitochondria
 This also happened with a cyanobacteria,
which became chloroplast
 Reproduced along with host cell
Endosymbiontic Theory
Introduction to
Darwinian Evolution
Important Terminology
 Evolution
 Accumulation of inherited changes within
populations over time
 Population
 Group of individuals of one species that live in the
same geographic area at the same time
 Species
 Group of organisms with similar structure, function,
and behavior capable of interbreeding
Pre-Darwinian Ideas
 Aristotle
(384–322 B.C.E.)
 Saw evidence of natural affinities
 Leonardo
da Vinci (1452–1519)
 Correctly interpreted fossil rocks
 Jean
Baptiste de Lamarck (1744–1829)
 First to propose that organisms undergo change
as a result of natural phenomenon
 Lamarck ideas discredited when Mendel’s
theories rediscovered around 1900
Darwin
&
Evolution
Voyage of the H.M.S. Beagle
 1831
 Basis
for Darwin’s theory of evolution
 Darwin observed similarities between
animals and plants
◦ Arid Galapagos Islands
◦ Humid South American mainland
Voyage of the H.M.S. Beagle
Influences on Darwin
Principles of Geology by Lyell
 Artificial selection

 Breeders developing many varieties of
domesticated animals in a few generations
 Plant varieties, such as kale and broccoli,
developed from wild cabbage
 Ideas
of Thomas Malthus
 Population growth not always desirable
 Population increases geometrically; food supply
increases arithmetically
Based on adaptations by organisms over
time:
 Inherited variations favorable to survival
persevere
 Unfavorable variations are eliminated
Theory of Evolution by Natural Selection
Proposed by both Darwin and Wallace
Based on four observations:
1. Genetic variation exists among individuals
2. Reproductive ability of species causes its
population to increase
3. Organisms compete for resources
4. Offspring with most favorable characteristics
is most likely to survive
Genetic variation in emerald tree boas
1.
2.
3.
4.
5.
Fossil Record
Comparative Embryology
Comparative Anatomy
Biogeography
DNA Homology
Direct evidence of evolution comes from
fossils
 Shows
life has evolved through time
Exposed layers
of
sedimentary
rock
Fossils develop
in different
ways
Fossil
intermediates
in whale evolution
Determining
the age
of fossils:
radioisotope
decay
Evidence for evolution from comparative
anatomy
 Homologous
features
 Derive from same structure in common ancestor
 Vestigial
structures
 Remnants of structures indicating adaptation
Homology in plants
Convergent evolution: mammals who eat ants and
termites
Vestigial structures
Evidence of Evolution from Biogeography
◦ Study of past and present geographic
distribution of organisms
◦ Continental drift has played a major role in
evolution
Continental drift
Evidence for evolution from developmental
biology
 Proteins
and DNA contain record of
evolutionary change
 Phylogeny
 Evolutionary history of group of related species
 Phylogenetic
trees
 Diagrams showing lines of descent based on
molecular data
Phylogenetic
tree of
whales and
their closest
living relatives

Intergenerational changes in allele or
genotype frequencies within a population

Often involves relatively small or minor
changes, usually over a few generations
Changes in allele frequencies of a population
caused by microevolutionary processes:
1.
2.
3.
4.
5.
Nonrandom mating
Mutation
Genetic drift
Gene flow
Natural selection
Nonrandom Mating
Inbreeding
 Increases the frequency of similar alleles
 Prevents genetic variation

Mutation

Source of new alleles in a population

Increases genetic variability acted on by
natural selection
Genetic drift
Random change in allele frequencies of a
small population
 Decreases genetic variation within a
population
 Changes it causes are usually not adaptive

 Ex: Polydactyl traits in Northern Amish Communities
Genetic drift

Bottleneck is a sudden decrease in population
size caused by adverse environmental factors

Founder effect is genetic drift occurring when
a small population colonizes a new area
Gene flow

Movement of alleles caused by migration of
individuals between populations

Causes changes in allele frequencies
Natural selection
1.
2.
3.
Causes changes in allele frequencies leading
to adaptation
Operates on an organism’s phenotype
Changes genetic composition of a
population favorably for a particular
environment

Modes of Natural Selection
Stabilizing Selection
◦ Favors the mean (average individuals)
◦ Favors the “already well-adapted organisms”
◦ If the environment remains unchanged, the “fittest”
organisms will also remain unchanged
 Ex: Horseshoe Crabs & Ginkgo Trees(have not changed for
millions of years)

Directional Selection
◦ Favors one phenotypic extreme over the others
and eventually leads to change in a population.
◦ It occurs when organisms must adapt to changes
conditions in the environment.
 Ex: Pesticide & antibiotic resistance (organisms
learn to adapt and withstand a harmful chemical)

Disruptive Selection
◦ Favors two or more phenotypic extremes.
◦ Ex: African orange butterflies can range in color from orange
to blue. The orange and blue forms mimic foul-tasting species,
so predators avoid them. The colors in-between do not ward
off predators, so butterflies with those colors are eaten more
commonly. As a result, only butterflies with extreme colors
(orange & blue) survive.
Modes of Natural Selection
(a) No selection
(b) Stabilizing selection
Modes of Natural Selection
(c) Directional selection
(d) Disruptive selection
Genetic variation in populations caused by:
1.
2.
Mutation
Sexual reproduction
◦ Allows new phenotypes
Speciation &
Macroevolution
Reproductive Isolating Mechanisms
 Prevent
gene flow between species. Two
types:
1. Prezygotic Barriers
 Prevent mating or fertilization.
2. Postzygotic Barriers
 Reproductive failure after fertilization
1.
2.
3.
4.
5.
Temporal Isolation
Habitat Isolation
Gametic Isolation
Begavioral Isolation
Mechanical Isolation
1. Temporal Isolation
Mating at different
times of year
 Mating at different
times of day

2. Habitat Isolation
◦ Different habitats in the same area
3. Gametic Isolation
◦ Incompatible egg and sperm
◦ Molecular recognition on the surface of the
cells
4. Behavioral (sexual) Isolation
◦ Required courtship behaviors
The male satin
bowerbird
builds a bower
of twigs
(a dark tunnel)
to attract
females
5. Mechanical Isolation
◦ Incompatible genital organs
Only small
bees can
land on the
petal of the
black sage
Only large
bees brush
against the
stamens of
the white
sage
Hybrid Inviability
 Zygote forms, but hybrid embryos die
when genetic regulation fails during
development
Hybrid Sterility
 problems during meiosis cause abnormal
gametes
Hybrid Breakdown
 Hybrid cannot reproduce because of some
defect
Formation of New Species: Speciation
When a population becomes
reproductively isolated the separated
gene pools diverge & genetic exchange
stops, as a result a new species is formed
Types of Speciation Mechanisms:
1.
2.
3.
Allopatric Speciation
Sympatric Speciation
Artificial Speciation
Allopatric Speciation
 a population splits into two geographically
isolated populations (for example, by habitat
fragmentation due to geographical changes or
social change such as emigration).
 Most common form of speciation
 Genetic drift in small populations
Examples:
1. Galapagos tortoises that live in separate, but
nearby islands
2. Squirrel species separated by the Grand Canyon
Abigdoni Tortoises
Chathamensis Tortoises
Porteri Tortoises
Squirrel species separated by the Grand
Canyon have diverged in fur color
Sympatric speciation
 Refers
to the formation of two or more
descendant species from a single
ancestral species all occupying the same
geographic location
 Populations diverge and each occupies a
new ecological niche
Examples:
1. Finches in Galapagos Islands
2. Maggot Flies in North America

The finches live in the
same habitat but each
has a different niche.
Fossil record often lacks transitional forms
between two species
 Is the fossil record simply incomplete?
 Or does it accurately reflect evolution as it
really occurs?

 Long
periods of stasis (~2 My)
 Punctuated by periods of rapid
speciation (~100,000 y)
 Triggered by changes in the environment
 Abrupt appearance of new species in the
fossil record
Continuous evolution over long periods
 The traditional view
 Populations gradually accumulate adaptations
 Different selective pressures in different
environments

Gradualism
Punctuated
Equilibrium
 Large-scale
phenotypic changes in
populations, classified at the species
level or higher
 Characterized by:
1. Appearance of evolutionary novelties
2. Adaptive Radiation Patterns
3. Mass extinctions
Allometric Growth
◦ Varied rates of growth for different parts of
the body
◦ A change in development can result in a new
species when the change is adaptive
Allometric Growth
Paedomorphosis
 Retention
of juvenile characteristics in
the adult
 A change in the timing of development
Paedomorphosis
in an axolotl
salamander
Adaptive Radiation
 Speciation
fills new ecological niches
 New adaptive zones may appear when
the environment changes
 One species colonizes an island and
diversifies into new species
Adaptive
radiation
Extinction of Species
 Facilitates
evolution by opening adaptive
zones
 Background extinction at a steady rate
Mass extinctions
 Five
or six mass extinctions of many
species and higher taxonomic groups
 Major climate changes
 Catastrophes such as asteroid impacts
Mass extinction of the archosaurs
The Evolution of
Primates
Primate evolution
All Mammals
 Endothermic (warm blooded)
 Body hair
 Feed young with milk from mammary glands
 Most are viviparous (give live birth)
Placental Mammals
 Placenta exchanges materials between
mother and fetus
 Newborns are more developed than
marsupials
ALL Primates:
 Are mammals
 Have 5 grasping digits
 Have pposable thumb or toe
 Have long, freely moving limbs
 Have eyes in front of the head
 Have large brains
Primate hands
and feet

Suborder Prosimii
◦ Lemurs

Suborder Tarsiiformes
◦ Tarsiers

Suborder Anthropoidae
◦ Monkeys, apes, humans
Anthropoids
 Old and new world monkeys
 Apes and humans
Hominoids
 Apes
 Gibbons
 Orangutans
 Gorillas
 Chimpanzees
 Humans
New world monkey
Old world monkey
Hominids
 Humans & extinct human ancestors
 Differences between ape and human skeletons
 Human adaptations for bipedal life on the ground
 Complex curvature of the spine
 Shorter, broader pelvis
 Foramen magnum at base of skull
 First toe aligned with other toes
Human and Gorilla Skeletons
Human and Gorilla Heads