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IB 169 Introduction/Overview Evolutionary Medicine
Lecture Topic #1 (Text pp. xiii-xvi; pp. 257-268, 272-275,
17/Box 1.7, Science Ellison pdf; PNAS Nesse pdf; PRSB Stearns
pdf)
Instructor: Tom Carlson Department of Integrative Biology
University of California, Berkeley
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IB 169 Syllabus Instructor: Tom Carlson [email protected]
Office Hours: Tuesday 3:40-4:00 PM, Wednesday
11:10-12:00, Thursday 12:40-1:30 in VLSB 1098 Lectures:
11:00-12:30 Tuesdays and Thursdays in
in 145 Dwinelle Discussion section one hour a week GSIs: Dena
Block [email protected] (Friday
sections) Charlotte Jennings [email protected]
(Wednesday sections) Katya Mack [email protected]
(Monday
sections) 2
IB 169 Required textbook
Gluckman, Peter; Alan Beedle; and Mark Hanson. 2009. Principles
of Evolutionary Medicine, Oxford University Press."
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Lecture material Lectures are based on information in
required text as well as other sources. Additional PDFs of key
articles from sources
other than the required text will be made available on IB 169
bspace site.
PDFs of lecture powerpoint slides will be downloaded onto IB 169
course website at bspace.berkeley.edu before each lecture.
Midterms & Final Exam material will be based only on
material presented in the lectures.
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Midterm & Final Exams
Midterm #1 on 2/19/15 at 11:00 AM (30% of grade)
Midterm #2 on 4/2/15 at 11:00 AM (30% of grade)
Final Exam: 5/14/15 at 8:00 AM (30% of grade)
Discussion section: 10% of grade
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IB 169 Lecture Topics
Overview of evolutionary medicine & evolutionary pathways to
disease
Primate evolution & diversity Ape evolution & diversity
Hominin evolution & diversity Human migration &
evolution
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IB 169 Lecture Topics
Evolutionary Theory Genetics: Molecular Basis of
Variation & Inheritance Evolution, Development &
Phenotypes Epigenetics
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IB 169 Lecture Topics
Life histories Puberty & Menarche Menopause Reproduction
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IB 169 Lecture Topics
Culture, Psychology, Stress and HPA & HPG axes
Diet and Metabolism Host-Pathogen Interactions Cancer
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Human Clinical Case Presentations
Human Clinical Case Presentations on a spectrum of different
disease pathophysiological states will be presented throughout the
course
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Evo-Devo Interaction of evolution with embryonic
and other developmental processes Role of genes regulating
embryonic
development. Epigenetic influences on development. The role of
developmental plasticity in
evolution.
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Life history
The traits that affect an organisms life cycle, especially the
schedule of reproduction and survival.
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Stress and endocrine and autonomic systems
Evolution of human endocrine system and autonomic nervous system
and responses to stress.
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Nutrition and metabolism
Evolution of human diet. Emergence of obesity, insulin
resistance, and metabolic syndrome, and the integrative
understanding of genetic, developmental, environmental, and
behavioral risk factors for these diseases.
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Infectious diseases Host-pathogen interaction Pathogen
resistance Pathogen virulence Human host immune response
Vaccinations Antimicrobial medications Emerging infectious
diseases
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Human defense
Hygiene theory. Autoimmune diseases.
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Cancer
Different evolutionary perspectives on development of different
types of cancers.
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Medical terminology
Hx = history PE = physical exam Dx = diagnosis Tx = treatment Rx
= prescription
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Medical abbreviations CV = cardiovascular GI = gastrointestinal
GU = genitourinary DM = diabetes mellitus ID = infectious disease
OB = obstetrics GYN = gynecology OB/GYN = obstetrics &
gynecology
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History of evolution of evolutionary thought
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Evolution of evolutionary thought Linnaeus 1758: hierarchical
classification of organisms;
(Systema Naturae book by Linnaeus) Jean-Baptiste Lamarck early
1800s: proposed the
concept of evolution Darwin & Wallace 1858-1859: natural
selection and
evolution (Origin of Species 1859 by Darwin) Mendel 1866:
inheritance in peas ("Experiments in plant
hybridization". Journal Royal Horticultural Society 26: 132,
1866)
Ronald A. Fisher, Julian Huxley and others 1936-1947: modern
synthesis (Evolution: The Modern Synthesis, 1942 by Julian
Huxley)
Watson & Crick 1953: double helix of DNA (Nature 171,
738-740, 1953)
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Linnaeus classification system of organisms in 1758
Carl Linnaeus in 1758, published his Systema Naturae book
describing thousands of plants, fungi, and animals in a
hierarchical classification system of taxonomy with species,
genera, families, orders, classes, phyla, & kingdoms.
Binomial system of species names e.g., Homo sapiens
His underlying definition of a species was the ability of
individuals within the species to interbreed and produce viable
offspring.
However, Linnaeus thought that species were fixed and
immutable.
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Jean-Baptiste Lamarck contributions to
evolutionary thought In early 1800s, Jean-Baptiste Lamarck
from France proposed that evolution occurred and proceeded in
accordance to natural laws.
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Darwin & Natural Selection Charles Darwin first described
his ideas
of evolution and natural history in 1842, but they were not
widely circulated.
Charles Darwin and Alfred Russell Wallace independently
described natural selection in 1858.
Darwin published On the Origin of Species in 1859 which
describes how natural selection provides a mechanistic explanation
of how species change over time and how new species evolve.
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Natural selection
Darwin articulated that species were not immutable and that
through natural selection, selective retention of beneficial
variation can be a mechanism for a species to change and
evolve.
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Gregory Mendel & Inheritance In 1866, Gregory Mendel
published his
article on the nature of inheritance in his experiments with
plants.
Unfortunately, the importance of Mendels research was not
appreciated until the early 1900s when it triggered the development
of the field of genetics.
The understanding of inheritance and genetics aided the
development of evolutionary science.
26
Modern Synthesis Between 1936-1947, Ronald A. Fisher and
other
scholars contributed to the integration of the fields of
genetics, evolutionary biology, systematics, morphology, ecology,
and quantitative statistics to create the Modern Synthesis.
Other contributors to this synthesis include Theodosius
Dobzhansky, J.D.S. Haldane, Julian Huxley, and G. Ledyard
Stebbins.
In 1942, Julian Huxley invented the term when he published his
book, Evolution: The Modern Synthesis.
While this synthesis is well understood today in the biological
sciences, its application to human biology and medicine is still
emerging.
27
Elucidation of DNA Structure In 1953, the elucidation of the
structure of DNA by Watson & Crick enabled evolutionary
processes to be understood at a biochemical level.
This discovery aided the further development of molecular
biology and evolutionary science.
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Human Genome mapped Completed in 2003 Human Genome Project
publicly funded by
the US government (International Human Genome Sequencing
Consortium, Nature 2001, 409 (6822): 860921)
Celera Genomics, private company headed by Craig Ventor, a US
researcher (Science 291 (5507): 13041351.)
20,500 genes in Homo sapiens 29
Evolution in medical education
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Medical Education in 1870 in University College, London
Thomas Huxley was the most powerful voice in Britain in 1870 in
medical education policy.
He did not include topics such as evolution and comparative
anatomy in medical curricula.
He stated that there was simply too much information already
required in medical school in the topics of human anatomy,
physiology, pathology, and pharmacology.
Today, integration of evolutionary biology into medical
education is still lacking.
31
2009 was the 150th anniversary of the publication of On the
Origin of Species
A joint committee of the Association of Medical Colleges and the
Howard Hughes Medical Institute recommended that a core competency
on scientific knowledge by future physicians includes an
understanding of evolution by natural selection.
In April 2009, a meeting, Evolution in Health and Medicine
sponsored by the National Academy of Sciences and the Institute of
Medicine where a panel of deans and faculty from leading medical
schools around the world endorsed incorporation of evolutionary
principles in medical curricula.
Unfortunately, instruction on evolution in medical school
education continues to be rare. 32
Education in medicine today Medical science has become dominated
by
relatively reductionist approaches looking at levels of
organization (gene, cell, tissue) individual organ systems, or
different disciplines (physiology, biochemistry, or anatomy),
without adequate attention on how these levels, systems, and
disciplines interrelate with our ecological environment and
evolutionary history.
Integration of evolutionary and ecological perspectives
illuminates our understanding of the causes and mechanisms of
health and disease both in individuals and populations.
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An evolutionary perspective broadens the way physicians and
medical researchers think about
health and disease Enhances quality of diagnosis and
treatment of patients. Enhances our understanding of human
populations and contributes to design of appropriate public
health interventions.
Helps identify important research questions to explore.
34
Reasons evolution has not been included in medical education
Crowded medical curriculum. Bias against the relevance of
evolution in
understanding health and disease. Lack of appropriately skilled
faculty members
in medical schools available to teach evolutionary
principles.
Up until recently, there has been a lack of appropriate, user
friendly materials to teach the topic of evolutionary medicine.
35
Books on evolutionary medicine Fortunately, in recent years,
useful books and articles
on this topic have become more available. In 1994, Randolph
Nesse and George Williams
published the groundbreaking book entitled Why We Get Sick: The
New Science of Darwinian Medicine.
Since the publishing of this book, numerous other books and
edited editions on the topic of evolutionary medicine have been
published.
The 2009 publication or Principles of Evolutionary Medicine by
Gluckman, Beedle, and Hanson is the first specifically designed
textbook on evolutionary medicine.
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Evolutionary Medicine books in chronological order Nesse,
Randolph; Williams, George Williams. (1994). Why We Get
Sick: The New Science of Darwinian Medicine. Stearns, Stephen C.
(1999). Evolution in Health and Disease. New
York: Oxford University Press. Trevanthan, W.R., Smith, E. O.,
& McKenna, J. J. (1999). Evolutionary
Medicine. Oxford: Oxford University Press. Nabhan Gary Paul.
(2004). Why Some Like it Hot: Food, Genes, and
Cultural Diversity, Island Press. Barnes, E. (2005). Diseases
and Human Evolution. University of New
Mexico Press. pp 1-484. Trevanthan, W.R., Smith, E. O., &
McKenna, J. J. (2008). Evolutionary
Medicine and Health: New Perspectives, Oxford University Press,
Oxford, pp 1-532.
Stearns, S. C., and Koella, J. K. (2008). Evolution in Health
and Disease, 2nd Edn. Oxford University Press, Oxford. pp.
1-374.
Gluckman, Peter; Alan Beedle; and Mark Hanson. (2009).
Principles of Evolutionary Medicine, Oxford University Press.
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Microevolution & Macroevolution (Futuyma 2009,
Evolution)
Microevolution: usually refers to slight relatively short term
changes within a species.
Macroevolution: usually meaning the evolution of substantial
phenotype changes, typically great enough to place the changed
lineage into a distinct new species or higher taxon.
38
Trait Any detectable variation in a genetic character. A trait
is a distinct variant of a phenotypic character of
an organism that may be inherited, environmentally determined,
or be a combination of the two.
Traits typically result from the combined action of several
genes, though some traits are expressed by a single gene
(monogenic).
No trait is perfect. Every trait must be analyzed in terms of
the benefits
and costs of the trade-offs inherent in a particular trait.
Natural selection favors traits that improve the fitness
(reproductive success) of individuals and their kin. 39
Fitness Fitness = reproductive success. Selection operates to
enhance fitness. Enhancement of fitness, does not necessarily
operate to enhance health or longevity Fitness involves
trade-offs which enhance
reproductive success even if they incur other costs such as a
shorter life.
Evolutionary biology considers how an organism trades-off one
component of its biology against others to enhance fitness.
40
Proximate versus ultimate causes of disease
Most medical training focuses on understanding the immediate
mechanistic pathophysiologic pathways leading to the disease, the
so-called proximate causes.
In this course we will explore the ultimate causes, the so
called evolutionary factors which result in the emergence of
pathways to health or disease.
41
Ultimate causes of human disease and health
How has evolution led to a particular trait or set of traits
persisting?
Is the trait helpful or not helpful under the present
circumstances?
Have the limits of acclimatization been exceeded due to a
mismatch of evolutionary history, ancestral environment, and
present environment?
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Proximate causes The anatomical, physiological,
molecular, and pathophysiological mechanisms that lead to a
biological phenomenon.
Insulin resistance leads to type 2 diabetes mellitus.
Mutation in hemoglobin gene leads to sickle cell anemia.
Exposure to tuberculosis may lead to pulmonary TB.
43
Ultimate causes The ultimate cause is the evolutionary
explanation
for why a person gets sick under certain circumstances.
To understand the ultimate cause, the following questions must
be asked:
Why are some people prone to developing insulin resistance and
type 2 diabetes mellitus?
Why do certain populations carry a mutation in hemoglobin gene
which leads to sickle cell anemia?
Why do some people develop pulmonary tuberculosis as a result of
being exposed to tuberculosis while other people do not?
44
Normal versus abnormal Definitions of normality,
abnormality,
and disease are not absolute and are influenced by the
environmental context of the individual and the individual
variation in phenotype.
45
Normal vs abnormal Modern medical thinking has a tendency to
dichotomize into normal or healthy and abnormal or
unhealthy/pathological.
However, such assessments are contextual: an adaptation (e.g.,
sickle cell) may prevent a certain disease (i.e., malaria) in a
heterozygous carrier and thus make a person healthy, while this
same adaptation puts a homozygous individual at risk for another
disease (sickle cell crisis) and thus makes the individual
unhealthy.
We will explore these trade-offs in this course.
46
Determinants of an individuals biological health status
Environment: physical, biological, and social world they lives
in.
Development: which stage of development they are in.
Behavior: how they live in world. Physiology/anatomy: how they
function in
world. Transgenerational ancestral influences
mediated through genetic and cultural inheritance. 47
Relevant histories in systematic evolutionary framework
#1: Medical history of the complaint/illness. #2: Developmental
history of the individual since
conception. #3: Evolutionary history of the individuals lineage.
Hx of probands (persons) population (including
genetics, drift, isolation, & migration) Hx of hominid clade
(including consideration of how
our environment has changed) Assessment of all these histories
is essential for a
comprehensive understanding of how an individual responds to
their environment.
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Evolutionary Pathways to Disease and/or Health
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Evolutionary Pathways to Disease and/or Health An evolutionary
matched environment. An evolutionary mismatched or novel
environment. Outcomes of demographic history. Outcomes of cultural
history. Outcome of evolutionary constraints. Sexual selection and
sexual competition and their
consequences. Life-history and/or developmental associated
factors. Antagonistic pleiotropy. A harmful allele when homozygous
is maintained by heterozygote
advantage. Effects of deleterious allele does not become
apparent until after
reproductive age. Spontaneous mutations for a deleterious gene
defect replace
alleles eliminated by selection. Exaptation. Excessive and
uncontrolled defense mechanisms. Fighting the evolutionary arms
race with microbes.
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An evolutionary mismatched or novel
environment
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An evolutionary mismatched or novel environment
The biological processes that determine our present structure
and function may have evolved in very different environments
compared to those we now live in.
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An evolutionary mismatched or novel environment
Evolutionary change of our biological structure and function is
slow while our physical, nutritional, and social environments may
be changing relatively quickly.
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An evolutionary mismatched or novel environment
Many humans now live in environments that are very different
from those in which our ancestors lived and evolved.
These environmental mismatches can challenge our health.
Constraints on evolutionary processes (the speed, substrate, or
direction of selection, or in scope of plasticity) in the presence
of environmental novelty can lead to ill health.
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An evolutionary mismatched or novel environment
Many populations of people are living in the same geographical
area where their ancestors emerged, however, the ecological,
nutritional, and/or physical activity environment has changed
compared to the environment of their ancestors.
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An evolutionary mismatched or novel environment
The ancestral Homo sapiens diet and level of exercise was very
different than the contemporary sedentery lifestyle with diet of
highly processed foods.
The mismatch between the ancestral and contemporary diet and
exercise regimes has resulted in dramatic increase in rates of
obesity, insulin resistance, type 2 diabetes mellitus, and
cardiovascular disease.
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An evolutionary mismatched or novel environment
Demographic history of migration can result in an evolutionary
mismatched environment.
Some populations of people have a demographic history of
migration which has resulted in a contemporary population living in
a novel (and potentially mismatched) environment compared to their
ancestors.
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Outcomes of demographic history
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Outcomes of demographic history A persons evolutionary history
includes the
adaptations of his or her ancestral lineage to their
ecosystems/environments.
A person may now live in a different ecosystem/environment where
the ancestral lineage adaptations may be maladaptive.
For example if a person with a evolutionary history of ancestors
from a far northern latitude (e.g., Norway) migrates close to the
equator, their level of skin melanin will be maladaptive to the
high levels of UV radiation at these latitudes.
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Outcomes of demographic history
Homo sapiens migrated out of Africa about 60,000 years ago.
Depending on where they migrated to, humans may have passed
through population bottlenecks which generated founder effects.
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Outcomes of cultural history
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Outcomes of cultural history Social behaviors characteristic of
a
persons cultural group which can influence health and
disease.
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Outcomes of cultural history
A persons family, peers, and/or broader culture may have very
specific practices of what kind of food they eat which can
influence health and disease; a persons choice of how they eat is
influenced by their culture.
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Outcomes of cultural history A womans family, peers, and/or
broader culture may have strong opinions on how a female should
approach labor and delivery e.g., whether she plans to get an
epidural for labor or a scheduled C-section for delivery; this can
influence a womans choice on how she approaches birth options.
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Outcomes of cultural history A womans family, peers, and/or
broader
culture may have strong opinions on whether a female should
choose to feed her infant breast milk or formula; this can
influence a womans choice on how she approaches infant feeding
which influences the health of the infant.
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Results of evolutionary constraints
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Result of evolutionary constraints
Bipedal walking results in constraints on size of pelvic
inlet/outlet in females which can make some newborn deliveries
difficult.
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Results of evolutionary constraints
The change in shape and position of larynx necessary for human
speech has resulted in increased likelihood of sleep apnea.
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Life-history and/or developmental
associated factors
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Life-history and/or developmental associated factors
The human life-course strategy is one of deployment of resources
in the period up to peak reproductive performance, but trading-off
that investment against the associated loss of reparative function
in the post-reproductive period when a direct fitness advantage is
not possible.
Thus the primary investment in maintenance and repair is prior
to peak reproductive age and declines in post-reproductive
years.
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Life-history and/or developmental associated factors
Tradeoffs emerge when stress in early life cues an individual to
go into puberty early to increase the likelihood of reproduction,
however, earlier puberty has its inherent risks/costs.
The adaptive strategy of advancing puberty can result in a
mismatch between biological and psychosocial maturation.
Individuals who go into puberty earlier have a higher likelihood
of risk-taking behavior, depression, and even suicide. 71
Life-history and/or developmental associated factors
Early-life events with late life consequences e.g., infants with
early nutritional stress are at greater risk for developing
obesity, Type 2 diabetes, hypertension, and coronary artery disease
as adults, especially if they grow up in a sedentary environment
with abundant access to calories.
These early life events can trigger epigenetic changes
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dreammareSticky NoteThe body performs maintenance and repair
before the time when reproduction peaks. However, after that, the
body's maintenance and repair function wane.
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Antagonistic pleiotropy
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Antagonistic pleiotropy
Traits that have been selected to have benefits in early life
but then have detrimental effects later in life.
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Antagonistic pleiotropy Antagonistic pleiotropy is related to
life
history and describes traits which have been selected for
because they are advantageous in early life in promoting
reproductive fitness, but these same traits may have costs later in
life.
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Antagonistic pleiotropy An example is the presence of stem
cells in tissues which are adaptive during growth and
reproduction to promote tissue maintenance and repair, but the
persistence of certain stem cells can increase the risk of
neoplasia (cancer) later in life.
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Antagonistic pleiotropy, IGF-1 Nutritional factors acting at
multiple levels
regulate the secretion of insulin-like growth factor-1 (IGF-1)
and IGF-1 promotes fetal growth and muscle and skeletal growth
during childhood and adolescence and fitness in early reproductive
life.
However, in later life, high IGF-1 levels are associated with
and increased risk of certain cancers.
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Antagonistic pleiotropy testosterone
An example of this is the hormone testosterone, which is
essential for enhancing fitness in males in early life and in young
and middle adult years, however, in later life, testosterone can
increase risk of prostate cancer and heart disease.
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dreammareSticky NoteEarly advantages: Allow fetal growth,
muscular growth, skeletal growth, and fitness for childhood and
adolescence
Late disadvantage: increased risk of certain cancer.
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Antagonistic pleiotropy Given the higher rates in extrinsic
mortality and shorter lifespans in humans until recent
centuries, the negative effects in later life of such antagonistic
pleiotropic selection would have been largely hidden, further
favoring selection for the beneficial early-life effects.
79
Antagonistic pleiotropy (Fig. 5.8) Mutations that may improve
early-life
reproductive fitness may have deleterious effects in older age,
either by acting directly on older animals or by causing latent
damage in younger animals which is unmasked in older animals.
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Antagonistic pleiotropy
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Sexual selection
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Sexual selection (Futuyma 2009, Evolution)
Differential reproduction as a result of variation in the
ability to obtain mates.
Variation in the number of offspring produced as a consequence
of a competition for mates.
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Mate choice and ratio of testes/body size
Humans also have a relatively small testes weight/body size
compared to some other primates e.g., chimpanzees.
Relatively small testes as in humans is associated with
relatively monogamous mating systems.
Large testes like in chimpanzees are associated with promiscuous
mating systems where both females and males have multiple partners
(Fig 7.2); because there are multiple male partners, releasing more
sperm per ejaculation enhances sperm competition for egg. 84
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Testes are larger in males in species where there is a
multi-male mating system and
sperm competition would be predicted to be a factor in fitness
(Fig. 7.2)
85
Mate choice & sexual diphorphism Sexual dimorphism in body
size is associated with
polygynous mating systems, e.g., with gorillas. Human males are
on average taller and heavier than
females. Human males have a higher % of body mass as muscle
compared to females. However, humans have a relatively small
degree of
sexual dimorphism in body size and hence monogamous pair bonding
rather than extreme polygyny has been and continues to be most
typical for humans.
Some evolutionary biologists suggest that a mild partial-harem
mating system may have been the norm in human evolution.
86
Parental investment
The cost of reproduction is much higher for the female than the
male.
The female needs to gestate the fetus and breast feed the
infant.
Both parents can potentially provide considerable effort to
provide resources, protections, and education to their
offspring.
87
Evolutionary pathways that enable alleles that cause
monogenic disease to not be eliminated from the
population
88
Evolutionary pathways that enable alleles that cause monogenic
disease to
not be eliminated from the population Heterozygote advantage
(e.g., sickle cell
disease, cystic fibrosis, Tay-Sachs). Effects of the deleterious
allele may not
become apparent until after peak reproductive age (e.g.,
Huntingtons chorea).
Recurrent mutation may retain a deleterious allele in the
population (e.g., some forms of hemophilia).
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A harmful allele when homozygous
is maintained by heterozygote advantage
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Reason why alleles that cause monogenic disease persist in
population:
heterozygote advantage
The deleterious effects of the disease-promoting allele are
confined to or expressed most strongly in homozygotes, but
heterozygotes for the allele have some selective advantage over
homozygotes and this causes the frequency of the allele to be
maintained in the population.
91
Reason why alleles that cause monogenic disease persist in
population:
heterozygote advantage provides protection in the following
ways
Sickle cell allele protects against malaria Cystic fibrosis
allele protects against diarrhea and
tuberculosis Tay-Sachs allele protects against tuberculosis
Phenyketonuria allele: pregnant mothers who are
carriers of this allele have lower spontaneous abortion rates
and their fetuses are less likely to get cross-placental infection
by the potentially fatal mycotoxin, ocratoxin A (see Woolf, Am J
Hum Genetics, 1986, 38(5):773-5)
92
Effects of deleterious allele does not become
apparent until after reproductive age
93
Reason why alleles that cause monogenic disease persist in
population:
effects manifest after peak reproductive age
The effects of the deleterious allele may not become apparent
until after reproductive age, so the parent may pass on the allele
to a child before negative selection has had a chance to
operate.
An example of this is Huntingtons chorea/disease which has
symptoms that typically do not emerge until middle age adult
years.
Familial transmission accounts for more than 95% of new cases of
Huntington chorea/disease.
94
Spontaneous mutations for a deleterious gene defect replace
alleles
eliminated by selection
95
Spontaneous mutations for a deleterious gene defect replace
alleles eliminated by selection.
A deleterious allele is maintained in the population by
recurrent mutation.
Even if copies of the deleterious allele are lost from the
population because individuals carrying them die before
reproducing, the allele is created anew at some finite rate by
spontaneous mutation within the population.
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Reason why alleles that cause monogenic disease persist in
population:
recurrent spontaneous mutations Examples of this includes some
forms of
hemophilia as well as some aneuploid conditions e.g., Trisomy
13, and Trisomy 18.
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Reason why alleles that cause monogenic disease persist in
population: recurrent spontaneous mutations
Hemophilia: recessive sex-linked X chromosome disorder
Hemophilia A (clotting factor VIII deficiency) and Hemophilia B
(clotting factor IX deficiency) are the two most common forms of
hemophilia and both are maintained by new spontaneous mutations
that replace the alleles eliminated by negative selection.
Both are recessive sex-linked X chromosome disorders. Since
males have only one X chromosome, all males with
the allele have hemophilia. Females need to be homozygous with
allele on both X
chromosomes to have hemophilia; for this reason, it is rare in
females.
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Recessive sex-linked X chromosome inheritance Dominant allele X
(normal clotting)
Recessive allele x (abnormal clotting) Y is male sex
chromosome
Mom is carrier and Dad is unaffected
Sex chromosomes X x
X XX Unaffected
Xx Carrier
Y YX Unaffected
Yx Affected with hemophilia
Reason why alleles that cause monogenic disease persist in
population: recurrent spontaneous mutations
Hemophilia: recessive sex-linked X chromosome disorder
Mother and father has two daughters and two sons Mother is
carrier of hemophilia allele Father is unaffected One son is
unaffected One daughter is unaffected One daughter is carrier of
hemophilia allele One son is affected with hemophilia
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Recessive sex-linked X chromosome inheritance
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Excessive & uncontrolled defense mechanisms
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Excessive and uncontrolled defense mechanisms
Diseases of autoimmunity e.g., eczema, rheumatoid arthritis, and
inflammatory bowel disease can be considered as situations where
the normal evolved processes of defense are inappropriately and
excessively activated causing persons own antibodies to attack
their own tissues.
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Fighting the evolutionary arms race
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Fighting the evolutionary arms race
Humans are in a co-evolutionary relationship with viruses,
bacteria, fungi, and parasitic diseases.
The short generation times of microorganisms compared to the
long generation times of humans enables the microbes to evolve much
more rapidly to attempt to out-compete human defense systems.
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Fighting the evolutionary arms-race: Hypotheses on life history
strategies of
viruses, bacteria and other microbial pathogens
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Evaluation of biological phenomena through
Niko Tinbergens 4 questions
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Niko Tinbergens 4 questions applicable to biological
phenomena
#1: What is the mechanism underlying the phenomenon of
interest?
#2: How does the phenomenon develop during the lifetime of the
individual? That is, what is its ontogeny? (Ontogeny = the origin
and development of an individual organism from embryo to adult)
#3: What is the function of the phenomenon? How does it serve
the organisms interests?
#4: How did the phenomenon evolve? What is its evolutionary
history? Are there analogous phenomena in other species, and what
is their evolutionary relationship to humans? What is the evidence
for a selected origin?
108
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Niko Tinbergens 4 questions applicable to biological
phenomena
#1: What is the mechanism underlying the phenomenon of
interest?
109
Niko Tinbergens 4 questions applicable to biological
phenomena
#2: How does the phenomenon develop during the lifetime of the
individual? That is, what is its ontogeny? (ontogeny = the origin
and development of an individual organism from embryo to adult)
110
Niko Tinbergens 4 questions applicable to biological
phenomena
#3: What is the function of the phenomenon? How does it serve
the organisms interests?
111
Niko Tinbergens 4 questions applicable to biological
phenomena
#4: How did the phenomenon evolve? What is its evolutionary
history? Are there analogous phenomena in
other species, and what is their evolutionary relationship to
humans?
What is the evidence for a selected origin?
112
Answers to Tinbergens 4 questions on how and why we sweat when
frightened
Question #1: what is the mechanism underlying the phenomenon of
interest?
Question #1 answer: the proximate mechanism is activation of the
sympathetic nervous system fight/flight response which stimulates
sweat glands to sweat.
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Answers to Tinbergens 4 questions on how and why we sweat when
frightened
Question #2: How does the phenomenon develop during the lifetime
of the individual? That is, what is its ontogeny? (Ontogeny = the
origin & development of an individual organism from embryo to
adult)
Question #2 answer: Sweat gland innervation is not completely
mature until an infant is a few months of age. Also, the infant
must be old enough to have the ability to perceive a threat that
frightens and triggers the activation of the sympathetic nervous
system fight or flight response.
114
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Developmental plasticity of sweat glands continued answer to
question #2: Sweat glands are innervated in the
early weeks after birth and the density of innervation and thus
the capacity to sweat and tolerate extreme heat is influenced by
whether or not an infant is brought up in a cold or hot
environment.
This influences how an adult is able to sweat and tolerate
heat.
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Answers to Tinbergens 4 questions on how and why we sweat when
frightened
Question #3: What is the function of the phenomenon? How does it
serve the organisms interests?
Question #3 answer: Sympathetic fight/flight activation
generates increased heat in the body and the sweating helps
dissipate this excess heat and maintain normal body
temperature.
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Answers to Tinbergens 4 questions on how and why we sweat when
frightened
Question #4: How did the phenomenon evolve? What is its
evolutionary history? Are there analogous phenomena in other
species, and what is their evolutionary relationship to humans?
What is the evidence for a selected origin?
Question #4: answer: The evolution of the fear, fight, or flight
response is beneficial to
any species who faces the risk of predation. Since a successful
fight/flight response will require the capacity
to lose the excess heat to maintain normal body temperature,
homeothermic species may thermoregulate and lose heat by sweating
and/or panting.
Humans have evolved to sweat to thermoregulate. Thus sweating
may have evolved as a thermoregulatory system
but has been integrated into the fear response because of the
need to dissipate heat during the fight or flight response.
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