Transcript Super Quiz PowerPoint Lecture

AN INTRODUCTION TO
EVOLUTIONARY BIOLOGY
Acadec Super Quiz
2008-2009
Table of Contents
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What is Evolution?
History and Development of a Unifying Discipline
Latin America and Evolutionary Biology
Taxonomy, Classification, and Species
Mechanisms of Genetic Variation and Earth’s
Diversity
Select Topics in Evolutionary Biology
What is Evolution?
In this section:
o
o
o
o
Evolution and the Nature of
Science
The Rise of Evolutionary
Biology
The Development of
Evolutionary Theory
Modern Synthesis
Evidence for Evolution



Paleontologists study
fossils that give clues to
evolutionary processes
Tiktaalik is one such
fossil (early tetrapod)
Many other scientific
fields support the
theory of evolution
Evolution and Biology
•
•
•
Evolution provides an
explanation for the diversity
of life
The passing down of traits
is now explained by both
evolution and genetics
Mutations and natural
selection change
populations across multiple
generations
Small and Large Evolutionary Changes




Evolution produces small-scale changes over short periods
of time
 Example: Bacteria with antibiotic resistance
Large-scale changes occur over longer periods of time
(speciation)
Speciation and other large-scale changes can help
organisms inhabit new environments
 Example: The amniotic egg
Transitions like these, both large and small, can be found
in the fossil record
Evolution in Various Fields



Medicine: genetic analysis
of SARS virus
Agriculture: artificially
selecting wheat for
preferred traits
Industry: selecting
molecules for preferred
traits
Accepting Evidence of Evolution



Science relies on natural phenomena and
testable explanations
Some see the differing natures of science and
religion as being in conflict
Many scientists and theologians find no conflict


They can reconcile the two explanations of the
world
Evolution is still considered a theory, but has
been widely accepted as a fact
Descent with Modification
•
•
•
Dobzhansky says, “nothing in
biology makes sense except in
the light of evolution”
Evolution means change
between generations, or
“descent with modification”
A lineage is dependent on an
ancestor-descendent
relationship
Adaptation



Adaptation is “design”
in living things
Adaptation allows
organisms to survive
and reproduce
Examples include the
woodpecker’s beak and
camouflage
Evolution Before Darwin



Jean-Baptiste Lamarck wrote
Philosophic Zoologique in 1809
Lamarck argued that animals
“strived” to adapt (in place to
natural selection)
Others before Darwin believed
in species fixity

The idea that species never
change
Charles Darwin’s Arrival and Reception

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
After his voyage on the Beagle (1832-37), Darwin failed to
reconcile all current theories with the concept of
adaptation
Darwin created his own theory, which included the
concept of natural selection; Alfred Wallace also arrived at
this conclusion on his own
Darwin and Wallace presented their findings in 1858
The theory seemed to contradict the Bible and was
controversial among laymen, but was somewhat less so
among scientists
Flaws in the Theory of Evolution
•
•
Darwin’s theory of evolution
lacked a means of heredity,
meaning that there was no
mechanism to explain the
passing down of traits
Natural selection insufficiently
explained intermediate forms in
evolution (like proto-wings),
which were seen as better
explained by directed variation
Mendelian Genetics




Gregor Mendel explained how traits were passed down
from one generation to the next
His pea plant experiments (1856-63) explored concepts of
hybridization, and dominant and recessive phenotypes
Mendel mailed his findings to Darwin, who never looked
at them
A rediscovery of Mendelian inheritance in the early 1900s
led to a marriage between that theory and Darwin’s theory
of evolution
The Modern Synthesis
•
•
Fisher, Haldane, and Wright all
published materials supporting a
connection between Darwinian
evolution and Mendelian genetics
Combined with natural selection,
Mendelian inheritance answered
all the questions initially raised in
1858
Further Development of
Evolutionary Biology


Dobzhansky, Ford, Kettlewell, Mayr, Huxley,
and many others published materials on
genetics and evolution
The concepts of genotypes and gene pools
were incorporated into the new way of
thinking
Pre-Darwinian Evolutionary Thought
•
•
•
Ancient Greeks had theories on
evolution
James Ussher calculated the
earth’s age to be roughly 6,000
years old according to Genesis
Hutton, Lyell, Linnaeus, Buffon, E.
Darwin, W. Smith, Werner,
Cuvier, and Lamarck all
contributed to evolutionary
theory
Darwin and the Wallace-Darwin Theory
Darwin’s Theory
1.
2.
3.
4.
Adaptation
Variation
Over-reproduction
Natural selection
The Wallace-Darwin Theory
1.
2.
3.
4.
5.
Variability in traits
Over-reproduction
Variability in fitness
Fitness determines
success
Heritable traits and
change between
generations
Concepts in the Modern Synthesis

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
Genetic definition of evolution: “changes in allele
frequencies within populations”
Alleles are different versions of the same gene
Sources of these changes include genetic drift
(random changes), gene flow (exchanges between
populations), mutation pressure (copying errors
in genetic replication), and natural selection
(“survival of the fittest”)
Darwin and the Galapagos
In this section:
o The Voyage of the HMS
Beagle
o Chapter XVII: Galapagos
Archipelago (excerpt from
Darwin’s journal)
o Adaptive Radiation of
Darwin’s Finches
Darwin’s Background

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Raised in the Anglican Church
Loved science, went to medical
school (1825)
Dropped out after witnessing
surgery on a child with no
anesthesia
Joined Christ’s College at
Cambridge to study religion and
pursue science in his spare time
Before, During, and After the Beagle

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Two watershed events for Darwin: he re-read his
grandfather’s book and later witnessed his professor, Adam
Sedgwick, making a scientific error
Professor Henslow recommended Darwin for the Beagle
Darwin got along with Captain FitzRoy most of the time
During the voyage, Darwin collected many specimens of
flora and fauna
Back in England, he married and had 10 children
Darwin returned in poor health and stayed that way until
his death in 1882
The Voyage of the Beagle
Darwin’s Journal: Introduction



The text in the guide has been condensed
He gives credit to Owen, Waterhouse, Gould,
Jenyns, and Bell for influencing his work
He thanks several colleagues, especially
Professor John Henslow, who helped him
(from London) during the voyage
The Galapagos
September 15th-23rd

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There are ten Galapagos islands, all south of the
Equator, spotted with many craters, and volcanic in
origin
Chatham Island had relatively few plants, only
giant tortoises and some dull-colored birds
Charles Island had been frequented by buccaneers
and whalers, now inhabited by political exiles and
others
September 29th



Darwin visited Albemarle
Island and Narborough
Island
Both were covered with
black lava formations and
much of the islands was
sterile
There were black lizards
on Albemarle, as well as
yellow-brown ones
October 8th – James Island

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Darwin came across a group
of Spaniards, as well as other
small groups
Darwin learned that tortoise
meat can be prepared a
number of ways, and also
visited a salina
Measured the temperature in
various instances: the sand
was at least 137º F
Mice, Land Birds, and Water Birds
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Mus Galapagoensis was
the only indigenous
terrestrial mammal (and
mouse)
Darwin caught 26 land
birds, 25 of which were
unique to the archipelago
He also caught 11 water
birds, only 3 of which
were new species
Reptiles – the Tortoise
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Darwin discovered snakes,
lizards, tortoises, and sea turtles
He was surprised to find no toads
or frogs at all, even though the
environment seemed ideal for
them (perhaps egg differences?)
Tortoises travel to water sources,
sometimes four miles a day
The inhabitants believed the
tortoises to be deaf
Galapagos Lizards
Amblyrhynchus cristatus

Aquatic: lives on rocky sea
beaches
Amblyrhynchus Demarlii

Terrestrial: lives in burrows

Confined to the central islands

About a yard long

Smaller than the aquatic ones

Eats only seaweed


When frightened, it will allow
itself to be captured rather
than jump in the ocean
Eats cactus and other
vegetation

Will fight another lizard if
held next to it

When thrown in, it will come
out and return to the previous
spot
Shells, Insects, and Plants
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Darwin collected 90 shells, of which 47 were
previously unknown
Also collected several insects, most of which were
new species, but was surprised by how few there
were
Collected 100 new species of flowering plants
Was extremely surprised that fewer American
species of flora had not arrived at the islands
through natural means, given the short distance
between the two locations
The Tameness of Birds


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Darwin noted that birds were not
afraid of humans
The birds could be killed from
close range even after other birds
had been killed nearby
Darwin believed this to mean that
an instinct to avoid humans
would have to be passed down
through multiple generations
Adaptive Radiation


Adaptive radiation is
the diversification of
populations into
ecological niches
Four key concepts:
1.
2.
3.
4.
Origins
Speciation
Diversity
Disparity
Finches and Speciation
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
Darwin’s finches are
unique because of their
rapid diversification and
relative youth (3 MYA)
Allopatric speciation:
geographic separation
Sympatry can lead to
interbreeding with or
without fitness loss or no
interbreeding
Environmental Factors

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
Sympatry is not required for speciation
Not all islands might have existed when speciation began
A changing environment has significant effects on
adaptive radiation
Adaptation and Reproductive Isolation
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
1977 drought:
populations of small finches decreased (no small
seeds)
c. 1987 drought:
populations of large finches decreased (no large
seeds)
Dynamic equilibrium
Medium ground finches respond to cues from their
own species even when genetically able to hybridize
Finch Songs



Songs are learned traits passed down from
parent to offspring
Songs are particular to populations, not
necessarily entire species
Changes in environment can lead to natural
selection of different songs than those of a
parent species

Some changes to songs are by chance, not natural
selection alone
Adaptive Landscapes


Genotype and
phenotype frequencies
can be plotted on a 3D
landscape to determine
fitness
Areas of best fitness
are known as peaks
Adaptive Landscape and the River of Life
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Genotype and phenotype
frequencies can be plotted
on a 3D landscape to
determine fitness
Areas of best fitness are
known as peaks
The river of life is a visual
metaphor that may
replace the tree of life
(accuracy)
Taxonomy, Classification, and Species
In this section:
o
Classification
o
Taxonomy
Taxonomy, Traditional Classification, and
Cladograms

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Aristotle, John Ray, Carolus Linnaeus, and Robert
Whittaker all made significant contributions to taxonomy
Classifications from largest to smallest: Kingdom, Phylum,
Class, Order, Family, Genus, Species
Traditional classification focuses on common ancestry and
amount of divergence (major characters)
Cladograms focus on derived characteristics and
incorporate parsimony
Cladistics vs. Phenetics
Cladistics



Uses one or more derived
characters
Focuses on lineages and
common ancestry
Does not include overall
similarity
Phenetics

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
Uses algorithms to
determine similarity
Mathematical and
objective
Not used very often, but
helpful in objective
studies
Nomenclature

According to the International Code of Botanical
Nomenclature:
1) All taxa belong to a higher taxonomic group
2) The first name for a new species to be
published is considered valid (the “dibs” rule)
3) All new taxa must have an author
Definition of a Species

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Unlike all other categories (e.g. Kingdom),
species are not an artificial construct, and
actually exist in nature
Reproductive compatibility typically defines a
species (can these two animals have fertile
offspring?)
Asexual reproduction and grey areas make this
definition imperfect
Nomenclature and Classification


Taxonomic keys
help scientists
determine which
species an
organism is
Evolution and
lineages
determine the
closeness of
relationships in
classifying
multiple
organisms
Example of Dichotomous Key
Dichotomous keys
use technical
language in simple
steps to help
classification
Methods of Classification

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
Phenetics (numerical
taxonomy) uses
algorithms for an
objective classification
Cladistics is the most
popular and focuses on
lineages
Evolutionary taxonomy is
a combination of the two,
but considered arbitrary
by most scientists
Kingdom Systems


Kingdoms, ranging in number from three
to thirteen in some systems, are the largest
taxonomic group
The most common is a five kingdom
system, but it is being replaced by a six
kingdom model
Mechanisms of Genetic Variation
and Earth’s Diversity
In this section:
 The Evidence for Biological
Evolution
 Evolutionary Mechanisms
 Introduction to Evolutionary
Biology
 On the Many Origins of Species
 Speciation Standing in Place
Contributions From Other Areas
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Paleontology: fossils
Genetics: DNA
Astrophysics and
geology: age of the
earth
Physics and
chemistry: dating
methods
Anthropology:
human origins
Origins of the Universe and Earth

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
Georges Lemaitre: the
Big Bang theory
Background radiation
and distances allow for
dating of the universe
Universe: 14 BYA
Earth: 4.6 BYA
Moon: 4.4-4.5 BYA
Life’s Formation on Earth



Life is at least 3.5 billion
years old
Life required three
conditions to form: selfreproducing molecules
(RNA?), enough
molecules for variation,
and heritable variations
Protocells with variations
led to natural selection
The Fossil Record

Newer sediment deposits are
closer to the surface (and
those fossils resemble modern
organisms)

540 MYA: hard-bodied
organisms begin to dominate
the fossil record

Tiktaalik is a transitional form

Archaeopteryx: dinosaur-bird?
Homologous and Analogous Structures

Homologous structures are morphological characteristics in multiple
organisms that come from a single ancestral lineage (like human arms
and dog forelimbs)

Analogous structures look similar but do not come from a common
ancestral origin (like a dolphin’s and shark’s front fins/flippers)
Evolution and Geographical Distribution
Evolution and Geographical Distribution


Organisms live in so many different places because evolution
(via adaptive radiation) produces a variety of life forms
suited to ecological niches
Variations in precipitation levels, elevations, soils, and other
factors lead to rapid speciation in colonizing species
The Impact of DNA



DNA provides clues to past genetic changes
According to genetic information, humans are closely
related to chimpanzees, but increasingly far from
gorillas, mice, chickens, and puffer fish
DNA shows how much all life on Earth has in common
The Impact of DNA



DNA provides clues to past genetic changes
According to genetic information, humans are closely
related to chimpanzees, but increasingly far from
gorillas, mice, chickens, and puffer fish
DNA shows how much all life on Earth has in common
Humans and Chimps


Humans are 98%
genetically identical to
chimpanzees
In the case of one gene,
all of the differences
between humans and
chimps (only 5 out of
250 nucleotides) could
be matched on one side
by gorilla DNA
Human Evolution Timeline
6-7 MYA
last common ancestor of humans and chimps
4.1 MYA
Australopithecus afarensis (southern ape)
2.3 MYA
Homo habilis (skillful man)
1.8 MYA
Homo erectus (upright man)
200,000 years ago
Homo sapiens (wise man)
Evolutionary Mechanisms
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
Mutation, recombination, and gene flow
increase genetic variation
Mutations can be beneficial, deleterious, or
neutral
Genetic drift and natural selection decrease
genetic variation
Natural selection can be directional,
stabilizing, or disruptive
Soot
covered the
birch trees
Rapid
natural
selection
occurred
Soon after 1848
Biston
betularia
moths were
mainly
lightcolored
The Industrial Revolution
Before 1848
Case Study: Manchester Moths
The moths
were
primarily
darkcolored
The Evolutionary Process
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Gene mutation leads to
individuals being selected which
leads to population evolution
Microevolution:
gene mutations, small changes
Macroevolution:
speciation, big changes
Abiogenesis is the theory of
how living things first appeared
(this is NOT evolution)
Misconceptions



Morphological change and evolution are not
always bound to one another
Tiny changes might be the environment
acting on an organism, and not really
evolution
Organisms act on the environment just as
much as the environment acts on organisms
Genetic Variation

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


Mutation types: deletion, duplication,
inversion, insertion, translocation
Most animals are diploid (two alleles
for every gene at each locus)
Homozygous: same alleles
Heterozygous: two different alleles
Linkage disequilibrium alters allele
frequency
Mating



Assortative mating creates a non-random
distribution of alleles at a given locus
Non-random mating disrupts the HardyWeinberg equilibrium (allele frequencies)
Humans tend to mate with individuals of
the same race, meaning there are fewer
heterozygotes than predicted in the HardyWeinberg equilibrium
Natural Selection



Sometimes heterozygotes are
more fit than either
homozygotes (malaria)
Reproductive success: direct,
indirect, and inclusive fitness
Traits can end up used for
something other than their
original purpose

This process is called exaptation
Sexual Selection



Fitness is not always related to
being big, fast, or strong;
reproductive success is more
important
Females often select males
based on secondary
characteristics (peacock’s tail,
flashes in fireflies)
These characteristics may
reveal “good genes” or other
desirable qualities in males
Genetic Drift




Genetic drift is a random sampling error that occurs
naturally in all sexually-reproducing populations
Mutations and genetic drift generally balance each other
(mutations adding and drift subtracting)
Fisher and Wright disagreed on the importance of drift:
Fisher said it had a negligible effect on large populations,
while Wright said it was important in all populations
Unlike drift, the founder effect represents the remaining
genetic material after a population “crash”
Mutation and New Alleles

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

Most mutant alleles are neutral
 Some are harmful
 The smallest proportion are beneficial
Most new mutations are lost from the gene pool within
one generation
Neutral mutations lost due to random drift, deleterious
ones often selected against, and beneficial ones selected
for (but still often lost)
Beneficial mutations happen less frequently but thrive
most often
Recombination and Gene Flow




Recombination is the mixing of
maternal and paternal alleles during
cell replication
It increases variation by shuffling
genetic material
Gene flow is the addition of new
genes via population mixing
Gene flow between distantly related
species is horizontal transfer

Horizontal transfer is rare
Evolutionary Mechanisms – More

Genetic variation in a population is determined by the
balance of mechanisms




Natural selection can be positive or negative
Genetic drift is random, so it cannot be positive or negative
Recurrent mutation of a beneficial allele will help it reach
fixation
An allele that “catches a ride” with a beneficial allele is a
hitchhiker
Evolutionary Theory and Genetics




Lamarck’s theory and Darwin’s studies are two early
contributions to the new field
Mendel mailed Darwin his paper but Darwin never
opened it
Mendel’s work was not accepted early on because he only
studied discrete traits
Fisher’s Fundamental Theorem of Natural Selection
states that adaptive change in a given population is
proportional to the genetic variation present
DNA and RNA




DNA nucleotides:
adenine, guanine,
cytosine, thymine
RNA: uracil instead of
thymine; used in
transcription
Introns do not code,
exons do
Silent and replacement
sites evolve at different
rates
Evolution and Development

Vestigial structures are traces
of ancestry in modern
animals


Example: the human appendix
Common descent and
macroevolution are
supported by the
organization of traits (nested
patterns of evolution)
Speciation


Allopatric speciation
occurs with geographic
separation (most
common)
Sympatric speciation
(sometimes called
microallopatric
speciation) occurs
without geographic
separation
Extinction

Normal extinction occurs for many reasons


Mass extinction follows large-scale events


Competition, disappearing habitat, loss of food
source, etc.
Asteroid impact, climate change, humans
Mass extinction is followed by huge periods
of adaptive radiation because there are
empty niches to fill

Largest mass extinction: end of the Permian

Most famous mass extinction: CretaceousTertiary boundary
Punctuated Equilibrium

Punctuated equilibrium theory
states that evolution is not a
steady process


Instead, long periods of
relatively little evolution and
change are broken up by bursts
of rapid change
Proposed by Stephen Jay
Gould and Niles Eldredge
Evolution’s Importance



Evolution unites disparate
fields of biology
It explains the distribution
of traits across multiple
lineages and the variation
of life on Earth
It helps explain how
modern species came to be
Rhagoletis: A Case Study

The apple maggot Rhagoletis is
diverging into two species
Speciation began without
geographic separation
 Cause appears to be mating
habitat preference (apple and
hawthorn plants)


Studied first by Benjamin
Walsh, then by Guy Bush
Diversity in the Amazon



Speciation in the Amazon was
originally thought to occur
according to river separations
Research revealed that ancient
ridges were responsible for
some speciation
Mitochondrial DNA helped
separate the two causes
Sympatric Speciation and Frequency

Sympatric speciation is an explanation for
speciation that occurs with no apparent physical
separation
Has occurred with other flies, fish, butterflies
 The theory is established; now the focus is on how and
why

Sympatric Speciation Examples



Indigobirds – prefer mates
that know the same song
Cichlids – exist at different
depths within one lake
Palm Trees – initially
separated by soil
differences, now kept apart
by flowering timing
Sympatry: How Significant?



Some argue that the examples are still allopatric
on a small scale
Others argue that sympatry exists but is very
minor in the big picture of evolution
Some “clear cut” cases of allopatry are now
attributed to sympatry
Select Topics in Evolutionary Biology
In this section:
o
o
o
Jurassic Genome
Turn On: A
Revolution in the
Field of
Evolution?
Evolution and
Tinkering
Genome Sizes
Big genomes are found in animals
with big bone cells
 Small genomes are found in animals
with small bone cells
 Junk DNA: non-coding material
(98.5% of human DNA)

Fossils and Genomes

Birds evolved from theropods, which had
relatively small genomes


This contradicted the assumption that small
genomes evolved with flight
Genome sizes may be affected by natural
selection
Embryos and Evolution


Recapitulation:
“ontogeny recapitulates
phylogeny”
Two kinds of change



Through a lifetime
Through a lineage
Is embryonic
development a smallscale model of evolution?
Evo Devo’s Findings




Evo Devo is short for evolutionary developmental
biology
All animals are built from essentially the same
genes (including Hox genes)
Differences in animals are caused by the same
genes expressed at different times and places
Evolution is mostly a matter of “throwing
switches”
“Throwing Switches”


Gene expression, not gene
presence, is the guiding
force of evolution
Secret to this might lie in
the non-coding or “junk”
DNA

This may explain the wide
variation of life with so few
genes
Evo Devo: A Revolution?



Evo devo may be more of a paradigm shift
than a revolution
Darwin’s theory of evolution and Mendel’s
theory of inheritance were revolutions
Evo devo is not quite as significant a
breakthrough, but still important
The Nature of Science

Science follows a
method



Hypotheses have to be
testable
Science gives
provisional answers to
limited questions
Religion and
mythology can offer
comprehensive
answers
Hierarchy of Objects and Constraints



Sciences can be arranged in order of complexity
(physics to psychosociology)
Successive integrations in nature: analyzing
complex objects at all levels and determining
predictability
Constraints and history dictate evolutionary
systems
Natural Selection

Natural selection is the result of two
constraints
 Reproduction
 Ongoing

interaction with the environment
Natural selection gives direction to
changes
Natural Selection as a Tinkerer

Natural selection is not an engineer
 Engineers
use specific tools to achieve a planned
result with an ideal outcome in mind

It is a tinkerer
 It does

the best it can with what is available
Some evolutionary changes appear to be
constant, small-scale improvements (not long
term “projects”)
Results of Tinkering


Human females
spontaneously abort
nearly all malformed
fetuses before the first 3
weeks of pregnancy
Humans have
developed an
association between
pleasure and sex to spur
them to reproduce
Tinkering and the Human Brain


New structures
superimposed over old
ones
Conflicts between the
“visceral” brain and
the logical brain occur
because of these
additional structures
and connections
Conclusions




Darwin, Wallace, and many others represent the
foundation of the unifying theory of evolution
Theories about evolution are shifting because of new
genetic information and breakthroughs in other fields
Though most scientists agree evolution is a fact, there are
still questions about types of evolution (sympatric vs.
allopatric), its speed, and how exactly it occurs
Developing fields like genetics and evo devo are uncovering
new information and raising even more questions