Comprehensive Biology and Evolutionary Adaptations: Heritability, Altruism, Senescence, and Host-Parasite Dynamics

Explain genetic/physiological adaptations to underwater foraging among the Bajau

They can hold their breath for 5-13 minutes, experience vasoconstriction to restrict (and reroute) blood flow to necessary organs, and have bradycardia to lower oxygen consumption.

Why does heritability increase as environmental influences decrease?

Measure of how much of phenotypic variation is due to genetic influences vs environmental influences. it increasease because th genetic influence is taking over. overall genetic differences explain a larger share of the variation—so heritability increases.

What's a good example of heritability increase as environmental influences decrease phenomenon from lecture?

An example is myopia in Inuit children, where parental eyesight did not affect the children's eyesight due to environmental factors.

What is heritablity?

Vp =Va + Ve. Additative genetic influence plys geentic influence. As ve decreases, va increases. Heritability is the proportion of trait variation in a population attributable to genetic variation vs environmental variation. It indicates how much of the trait's variation can be explained by genetics.

What kinds of traits are most likely to have low heritability? Why?

Traits most closely linked with fitness tend to have low heritability. This is because of natural selection reducing genetic variation in those traits.

What is a defining characteristic of altruism? What does it require, in evolutionary terms?

Defining characteristic: lowering your fitness to raise the fitness of some other person.

Requires: a cost to the donor, benefit to recipient, and kin selection or reciprocal altruism.

Why was altruism thought to be an evolutionary dilemma?

Im not related to any of you and vice versa, yet i am. Why should we lower our fitness to assist another individual to pass their genes on. "where an individual lowers their own fitness to help another"

What is inclusive fitness?

Inclusive fitness is the sum of an individual's own reproductive success plus the reproductive success of their relatives (such as offspring, siblings, and cousins), weighted by the percentage of genes they share (e.g., 50% for full siblings, 25% for grandchildren)

How does inclusive fitness help to explain some forms of altruism?

resolves the "Darwinian dilemma" of altruism—where an individual lowers their own fitness to help another—through kin selection

What is c<rb?

hamilton's rule which represents the mathematical conditions required for the evolution of altruism via genetic selection- The cost to the individual (c) must be less than the benefit to the recipient (b) multiplied by their genetic relatedness (r)

what do the letters in c

• c represents the fitness costs to the individual performing the behavior.

• r represents the average coefficient of relatedness between the actor and the recipient.

• b represents the fitness benefits to all individuals involved in the behavior

how is c<rb related to altruism

shows that altruistic behavior can be favored by natural selection if it helps genetically related individuals enough to outweigh the actor's cost:

what characterises altruistic animals?

Characterises: willingness to lower their own fitness (reproductive potential) to raise the fitness of another.

what does reciprocal altruism require in order to evolve? Why does it require these things?

requires: long lives and long memories, sophisticated cognition, so they can track cheaters (i helped u but u didnt help me), a cost to the donor, for the helped party to give back later on

requires these things because it needs to have someone who expects a partner to help them later on. if tehy cant remember the past, they cannot recognize or punish those who cheat, which reduces the reliability (the point of it all).

What are the differences between organisational and activational effects of hormones?

Organisational: permanent effects in early life; organizing and shaping teh structure of the body/brain )(e.g., testosterone masculinizing the brain prenatally).)

Activational: influence transient behavioral effects due to changing hormone levels. appear late in life and are reversible((e.g., testosterone increasing aggression or mating behavior in adults).)

What factors affect testosterone levels?

Increase: extreme exercise, alcohol use(short term increas, long term decrease), competition,

Decrease: Age, body composition(aromatase converts testosterone into estrogen, reducing available testosterone), partnering and father hood, infection and injury

Does testosterone in men always decrease with age? What evidence is there for/against this idea?

Always, no, but goes general decrease.

Evidence: longitudinal studies showing consistent decline, there are outliers on graph of salivary testosterone.

What is the definition of anisogamy and how is it related to reproduction and mate choice?

definition: difference in gamete size

Related to reproduction female mammals (larger gamete; internal gestation and lactation) are required to invest more energy into reproduction/offspring

What is Bateman's principle?

when one sex invests more, members of the other sex will compete over them ie men fighting over women

What is senescence? How is it defined scientifically?

Senescence is the scientific term for aging.

Defined as: Progressive loss of function accompanied by decreasing fertility and increasing mortality with advancing age. causes increasing mortality rates, reduced dna repair rates, progressive dementia, decllining hormine production,declining immune function, and atrophy of muscle

Effects are: cumulative, deleterious, and intrinsic

What is the utility of death hypothesis?

argues that senescence (aging) and death are programmed adaptations rather than simple biological failures- designed to limit population size or accelerate the turnover of generations

what is the evolutionary logic behund teh utility of death hypothesis

tissues inevitably become "worn-out" over time, rendering older individuals "valueless to the species". Therefore, death is necessary to reduce competition over limited resources, as there is little biological need for life after reproduction unless the parent is actively caring for offspring

Evidence for the utility of death hypothesis

For: existence of The Hayflick Limit, Cellular Mortality, telomere shortening

Against: Predation: It is rare for wild animals to live long enough to reach a "worn-out" age; most die from external factors first.

• Gradualism: Senescence is a gradual process of decline, not a sudden death mechanism.

• Group Selection: The theory relies on group selection logic, which struggles to explain how such a trait persists if an individual "cheater" could mutate to live longer and out-reproduce others

What is the Hayflick Limit? What parts of DNA/chromosomes is it related to?

Limitations to the amount of time that cells can divide

Cellular sentence cells that re immortal Cancer cells

Related to: Cancer cells and telomeres that keep the cells from dying

What are the relationships between caloric intake/restriction and senescence?

Restriction and senescence: caloric restriction (CR) slows aging by lowering the metabolic rate

• Calorie restriction in lab animals slows senescence

- Reduces metabolic rate and oxidative stress

- Models estimate that maintaining a 20% CR starting at age 25 could extend life by 5 years.

Review the triangular longevity-body mass plot. What are each of the points on the triangle? Where to primates and humans fit into this plot? What kinds of animals are they closest to, and why?

its separated into 3 colors: S representing animals with small size and short lives, B represent animals like bats with small sizes and long lifespans and W is for animals like whales with large mass and long lifespans

- primates fall in between B and W, but at high upon hte y axis, showing that they live a much longer lives than predicted, far off of the main trend. Smaller primates, like monkeys, are will be clustered closer to B, yet live longer lives than other mammals of similar sizes, like dogs and cats, or rabbits. So the bigger a primate is, the longer their life span

What is the "selection shadow," ?

"Selection shadow" refers to the phenomenon where the force of natural selection declines with increasing age especially after reproductive period

It relates to senescence (aging) in the following ways:

• Weakened Selection: Genes expressed late in life have a smaller effect on an organism's fitness because fewer individuals survive to old age to reproduce.

• Mutation Accumulation: Consequently, harmful mutations that only manifest in late life are "immune" from natural selection; they are not removed by purifying selection because they occur after the organism has likely already passed on its genes.

and how does selection shadow relate to senescence?

It relates to senescence (aging) in the following ways:

• Weakened Selection: Genes expressed late in life have a smaller effect on an organism's fitness because fewer individuals survive to old age to reproduce.

• Mutation Accumulation: Consequently, harmful mutations that only manifest in late life are "immune" from natural selection; they are not removed by purifying selection because they occur after the organism has likely already passed on its genes.

• Result: Senescence is the side effect of these deleterious mutations accumulating across generations.

What is antagonistic pleiotropy?

Beneficial alleles that increase fitness but may have negative affects later in life

Explain the disposable soma hypothesis.

evolutionary theory proposed by Kirkwood (2000) that explains aging as a necessary trade-off in energy allocation... trade off between reproductive effort and survival, reproductive lifespan evolves as balance between costs/benefits oof increasing reproductive events per lifetime. Aging occurs because organisms trade off perfect body maintenance for reproduction—the body (“soma”) is only maintained as much as is needed to pass on genes.

evolutionary logic behind the disposable soma hypothesis

The hypothesis argues that senescence and death are programmed traits that evolved to benefit the species (group selection) by:

• Limiting population size and accelerating the turnover of generations.

• Removing individuals whose tissues have become "worn-out" and are consequently "valueless to the species".

• Reducing competition for limited resources, arguing there is little need for life after reproduction unless the parent is caring for offspring.

evidence for and against disposable soma hypothesis

Evidence for: Preventing reproduction in Drosophila (fruit flies) results in increased longevity

Evidence against: existence such as birds having high metabolic rates but long lives, or marsupials not living longer than other mammals of similar size

In what ways was were Paleolithic diets and lifestyles different from current Western diets and lifestyles?

Paleo diet:

lots of raw vegetables and fruit

Greater activity difference in the degree in nutrient variety

Greater fiber intake

More vitamins and minerals

Lower fats

Higher protein intake

Similar carb intake but different sources.

Agriculture changed things because of

Selective breeding of animals

Today: we dont move much, we eat unhealthily, and are super lazy overall.

What are the immunological processes underlying allergies?

IgE-mediated response, binding(IgE antibodies bind to the allergen and subsequently to mast cells and basophils), degranulation(releasing chemicals such as histamines and tryptase.), and recruitment(Additional immune cells, specifically basophils and eosinophils, are recruited to the area where they also degranulat).

What is the hygiene hypothesis?

rising prevalence of allergies and autoimmune diseases is caused by a lack of exposure to infectious agents, symbiotic microorganisms, and parasites during early childhood

What is the immunological mechanism involved with he hygiene hypothesis? How is it related to allergies and asthma?

Immunological responses:

Systemic Balance (Th1 vs. Th2),Regulatory Failure (The Role of IL-10) The hypothesis emphasizes the loss of regulatory mechanisms that evolved alongside parasites (specifically helminths/worms), Immediate Reaction (IgE and Mast Cells)

related to allergies and astha: reduced stimulation of regulatory pathways.

The immune system becomes biased toward TH2 responses, which drive IgE production, mast-cell activation, and eosinophilic inflammation.

This increases susceptibility to allergies and asthma.

What is the helminth hypothesis?

suggests that the human immune system evolved to coexist with parasites (specifically helminths). In the absence of these parasites due to modern sanitation, the immune system becomes deregulated and may overreact to innocuous antigen or IgE antibodies and the associated inflammatory responses evolved to "swarm" and combat macro-parasites like worms

What is the immunological mechanism involved in the helminth hypothesis? how is it related to allergy/asthma

- IgE Mismatch: IgE antibodies evolved to "swarm" multicellular parasites. Without these intended targets, the system may overproduce IgE or misdirect it toward harmless targets.

• Loss of Regulation (IL-10): Parasitic infections stimulate the production of IL-10, a broadly inhibitory cytokine that helps maintain immune homeostasis. Without infection, IL-10 levels drop, removing a critical "brake" on inflammation.

- related to allergies and asthma: Allergies and asthma are often IgE-mediated inflammatory responses. Under this hypothesis, these conditions arise because the immune system lacks the regulatory dampening (IL-10) provided by parasites, causing it to launch aggressive attacks against harmless environmental triggers (allergens) instead of worms

What is an autoimmune disease? What are some specific examples?

condition characterized by inflammatory dysregulation in which the immune system mistakenly attacks the body's own tissues. It is not a single condition but a category of over 100 different disorders

Examples: Rheumatoid arthritis, lupus, multiple sclerosis, etc.

Define "pathogen,"

any microorganism or agent/An infectious agent that can be transferred from host to host- pARASITE THAT CAN BE TRANSFERRED FROM HOST TO HOST

define "parasite,"

An organism living in or on another organism, feeding off of it, harming it, and showing some degree of adaptation to it-organism living in or on another, feeding off of it , showing some degree of adaptation to it and harming it

define "disease/illness"

the manifestation of the harm done by a pathogen to a host

What is the Red Queen hypothesis?

this hypothesis describes the constant, co-evolutionary struggle between hosts and parasites. It posits that organisms must constantly adapt and evolve not merely to gain an advantage, but simply to "stay still" (survive) against opposing organisms that are also evolving

How is red queens hypothesis related to host/pathogen co-evolution?

The hypothesis frames co-evolution as an "arms race" involving the reciprocal modification of evolutionary strategies. Because the fitness of the host depends on the pathogen (and vice versa), both must continuously evolve. Long-lived species (hosts) are often at a disadvantage compared to rapidly reproducing parasites

How does Fisher's Fundamental Theorem relate to the red queens hypothesis?

Relation to Fisher's Fundamental Theorem Fisher's Fundamental Theorem states that the rate of evolution is proportional to genetic variation. In the context of the Red Queen hypothesis, this means a population requires sufficient genetic variance to fuel the rapid adaptation necessary to keep up with its evolving parasites

the insufficient time hypothesis

This view suggests that high virulence is merely a temporary state caused by a lack of evolutionary time. It posits that because pathogens that harm their hosts ultimately harm themselves, host and pathogen should eventually evolve toward benign coexistence

Restricted Adaptation Hypothesis:

This hypothesis typically applies to vector-borne diseases. It argues that a pathogen cannot be benign in both the vector (e.g., a mosquito) and the host simultaneously. Therefore, high virulence in the host is a necessary trade-off for survival in the vector.

Adaptive Severity Hypothesis:

This hypothesis argues that virulence is an active, beneficial adaptation rather than a mistake or a trade-off. It suggests that specific symptoms (such as diarrhea in Cholera) are evolved mechanisms that directly aid the pathogen's survival, reproduction, and transmission. For example, this hypothesis predicts higher virulence when transmission does not rely on a mobile host (e.g., malaria

From where are many/most antibiotics derived from?

many antibiotics are naturally produced by bacteria and fungi as a tool for competition over resources

What does the origin of antibiotics imply about the evolution of antibiotic resistance genes?

antibiotic resistance is an ancient evolutionary adaptation rather than a modern development. Resistance genes—estimated to be 2 billion years old—evolved in nature long before human medical use. Consequently, modern antibiotics do not create resistance from scratch; they apply selection pressure that kills susceptible bacteria while allowing pre-existing resistant strains (often carrying resistance on plasmids or "accessory genomes") to survive and multiply

What are the ways that antibiotic resistance genes are transmitted from bacterium to bacterium?

antibiotic resistance genes are often carried on plasmids (extrachromosomal DNA), which function as an "accessory genome".

They are transmitted between bacteria through horizontal transfer mechanisms, including:

Transformation: The uptake of exogenous, foreign DNA from the environment.

• Transduction: The introduction of DNA from one bacterium to another via phage viruses.

• Gene Transfer Agents (GTAs): The transfer of random pieces of the host genome

What are the different mechanisms of antibiotic resistance?

Selection, De Novo Mutation, Horizontal Gene Transfer:

selection with antibiotic resistance

Antibiotics apply selection pressure that kills susceptible bacteria, allowing rare, pre-existing resistant strains to survive and multiply

De Novo Mutation with antibiotic resistance:

Resistance can arise from new mutations, though this is rare and slow (taking 600-700 generations) compared to acquiring pre-existing genes

Horizontal Gene Transfer with antibiotic resistance

Resistance genes are often carried on plasmids (extrachromosomal DNA functioning as an "accessory genome") and transferred between bacteria via:

◦ Transformation: The uptake of foreign DNA from the environment.

◦ Transduction: The transfer of DNA via phage viruses.

◦ Gene Transfer Agents (GTAs): The transfer of random pieces of the host genome.

Why aren't all bacteria resistant to antibiotics?

- Metabolic Cost and Growth Rates: Resistance genes are often carried on plasmids (extrachromosomal DNA). Maintaining and replicating these plasmids requires energy and resources. Consequently, bacteria that do not carry these plasmids (plasmid-free hosts) grow faster than those that do

- Competitive Disadvantage Because of the energy required to maintain resistance, resistant bacteria compete poorly against sensitive (non-resistant) bacteria in environments where antibiotics are absent. Without the specific selection pressure of the drug to kill off their competitors, the resistant bacteria are out-reproduced by the more efficient, non-resistant strains.

What is the biology and genetics of the sickle cell trait, and how is it related to malaria?

• Genotypes:

◦ SS (Homozygous Recessive): Individuals suffer from Sickle Cell Anemia. Under hypoxic stress, Red Blood Cells (RBCs) sickle, increasing blood viscosity and impairing oxygen transport. Historically, this resulted in high mortality before age 5.

◦ AS (Heterozygous): Individuals carry the "sickle cell trait" (one HbA and one HbS allele).

◦ AA (Homozygous Dominant): Individuals have normal hemoglobin but are fully vulnerable to malaria.

how is sickle cell related to malaria

Relationship to Malaria: The HbS allele persists due to a Heterozygote Advantage:

• Mechanism: In AS individuals, RBCs infected by the malaria parasite (Plasmodium) rupture prematurely, preventing the parasite from reproducing effectively.

• Evolutionary Context: This is a case of gene/culture co-evolution: the advent of agriculture created environments that increased mosquito populations, thereby increasing the selective pressure favoring the HbS allele.