Evol unit 2 part 2

What explains why humans today live longer on average than their ancestors?

Advances in sanitation and medicine, especially improvements associated with the Industrial Revolution, reduced infant mortality and helped more people survive to older ages.

What is the difference between average lifespan and maximum lifespan?

Average lifespan is the average age people live to; it has increased substantially. Maximum lifespan is the upper limit of human longevity, which the notes say has remained around 120 years.

What is cultural evolution in the context of human lifespan?

Changes in human knowledge, technology, sanitation, and medicine that improve survival and lifespan without requiring a genetic change in humans.

What demographic change is happening globally?

The global population is aging: older people make up a larger share of the population while children under five make up a smaller share.

Why is the proportion of young children shrinking in many populations?

People are choosing smaller family sizes, while more people survive into older ages. The decline is not simply because more children are dying.

How has the age structure of human populations changed historically?

Historically, there were proportionally more children than older people; that relationship has now shifted in many populations.

According to the notes, what proportion of Americans reach age 65?

The notes state that about 90% of Americans are alive at age 65, compared with about 50% at older ages in the comparison described in class.

What was the global annual birth rate around 1950 according to the notes?

About 37 births per 1,000 people per year.

What was the global annual birth rate around 2010 according to the notes?

About 19.5 births per 1,000 people per year.

What global annual birth rate do the notes project for 2050?

About 15 births per 1,000 people per year.

What annual birth rate for the United States is listed in the notes?

About 11 births per 1,000 people.

What is aging?

The process of growing older, beginning at birth.

What is senescence?

The process of bodily deterioration that occurs at older ages and increases vulnerability to disease.

What does morbidity mean in the context of aging?

Illness or reduced health; senescence increases vulnerability to disease and can involve a period of increasing morbidity.

Why is death costly in evolutionary terms?

Death can reduce fitness by limiting the number of descendants an individual produces.

Why does senescence raise an evolutionary question?

Building a human body is energetically expensive, so it raises the question of why natural selection does not maintain the body indefinitely.

What is the miscarriage rate mentioned in the notes?

The notes estimate that about 30â€"40% of fertilized embryos are miscarried; about half of those losses are attributed to chromosome-number abnormalities and other genomic problems.

What can cause problems beyond miscarriage during human development?

Additional problems can occur during fetal development or childhood.

Why is producing a human body energetically expensive?

Human development requires substantial energy and resources, from embryo development through growth and reproduction.

Why is natural selection often ineffective at extending lifespan late in life?

Natural selection is strongest when traits affect survival and reproduction earlier in life. Effects that appear after reproduction have less influence on how many descendants an individual leaves.

How does evolution occur across generations?

Evolution occurs across successive generations as inherited variation changes in populations. Without offspring carrying genetic variation forward, that variation cannot be passed into future generations.

Why might the children of a very fit parent not be equally fit?

Offspring inherit a combination of genetic variants and may not inherit the exact combination that contributed to the parent's fitness.

Why is the increase in modern human lifespan largely cultural rather than genetic?

Sanitation, medicine, and other technological and social changes have helped people survive longer without a comparable increase in the maximum human lifespan.

How does senescence happen in the body?

Different body parts and tissues gradually wear down and lose function; tissues differ in their capacity to regenerate.

Which tissues have high regenerative capacity according to the notes?

Skin, the gastrointestinal tract, and the liver.

What makes the liver an example of strong regeneration?

The liver can regrow after part of it is removed; both the remaining liver and a donated portion can grow toward their original size.

Which tissues have moderate regenerative capacity in the notes?

Muscle and bone.

What can happen to bone repair later in life?

Bone may not form new tissue as effectively after a break later in life, according to the notes.

Which tissues have low regenerative capacity according to the notes?

The heart, brain, and connective tissues.

How are connective tissues associated with aging in the notes?

Connective tissues can thin or deteriorate, contributing to conditions such as arthritis.

What did August Weismann propose about death?

He proposed that the death of older individuals could benefit the species by removing worn-out individuals.

What is the central problem with the idea that aging evolved for the good of the species?

Natural selection does not generally act at the level of what is best for an entire species. A trait must affect reproductive success or survival in ways that influence inherited variation.

Why is the claim that older individuals must die for the good of the species considered flawed?

It assumes evolution produces traits for the benefit of the species as a whole. The notes emphasize that natural selection does not work that way.

Why does natural selection have limited influence on post-reproductive humans?

After reproduction, an individual's traits generally have less direct effect on the number of descendants they produce, so selection against late-acting harmful effects is weaker.

What are the two major evolutionary theories of senescence in the notes?

Mutation accumulation theory and antagonistic pleiotropy.

What is mutation accumulation theory?

Harmful genetic mutations that act late in life can persist and accumulate because natural selection is less effective at removing them when their effects occur after reproduction.

Why are lethal mutations affecting embryos or young people more likely to be selected against?

They can prevent survival to reproduction or reduce reproductive success, so carriers may leave fewer descendants and the mutations can decrease in frequency.

Why can mutations that cause harm after age 70 persist in a population?

If their harmful effects appear after most reproduction has occurred, natural selection may be too weak to remove them effectively.

What does mutation accumulation theory say about late-acting harmful alleles?

They can remain in populations and accumulate because selection is less effective against effects that occur at older ages.

What is antagonistic pleiotropy?

A situation in which one allele affects multiple traits or aspects of the phenotype, with at least one beneficial effect and another harmful effect.

How can antagonistic pleiotropy contribute to senescence?

An allele that improves survival or reproduction early in life can be favored by natural selection even if it causes harmful effects later in life.

Why can an allele with harmful late-life effects increase in frequency?

If its early-life benefits improve reproductive success enough, natural selection may favor it despite its later harmful effects.

How do mutation accumulation and antagonistic pleiotropy differ?

Mutation accumulation is a passive process in which late-acting harmful mutations persist because selection is weak. Antagonistic pleiotropy involves an allele being actively favored because it benefits individuals earlier in life despite later costs.

Are mutation accumulation and antagonistic pleiotropy mutually exclusive?

No. Both processes may contribute to senescence.

How is Huntington's disease used as an example in the notes?

The notes present Huntington's disease as an example of antagonistic pleiotropy, stating that women with the allele have more children than women without it.

How are many cancers connected to mutation accumulation in the notes?

Many cancers are more common at older ages, fitting the idea that harmful mutations can accumulate when natural selection is less effective late in life.

At what biological levels can aging-related changes occur?

At the molecular level, including DNA, and at the cellular level as cells experience stress and damage.

What can cause mutations in body cells as people age?

Cell division, internal cellular stresses, and exposure to carcinogens can contribute to DNA mutations.

Why do most mutations in ordinary body cells not directly drive biological evolution?

Most body-cell mutations are not in sperm or egg cells, so they are generally not passed to the next generation.

What is p53?

A protein described in the notes as a major cancer-suppressing protein that helps determine the fate of cells with DNA damage.

What can p53 do when a cell has DNA damage?

It can trigger apoptosis, or programmed cell death, or allow a cell to survive if the damage is judged not too severe.

What is apoptosis?

Programmed cell death; it removes a cell from the body.

How can apoptosis contribute to senescence?

Removing damaged cells reduces the number of cells in a tissue and can contribute to age-related loss of function.

How can accumulated DNA mutations contribute to cancer?

If enough mutations accumulate in a living cell, the cell may develop into cancer.

How do aging-related mutations interact with inherited genetics?

Mutations that accumulate during life occur on top of genetic variants a person already inherited that may be associated with aging or cancer.

What is the relationship between senescence and morbidity in the notes?

Senescence is associated with increasing vulnerability to disease, and people may spend a substantial portion of later life experiencing greater morbidity and reduced bodily function.

Can cultural evolution eliminate senescence completely?

The notes suggest that medical innovation can treat diseases associated with senescence, but the genetic basis and complexity of aging make preventing aging itself difficult.

What evidence is offered against the idea that aging can simply be prevented?

Average lifespan has increased, but the maximum human lifespan has not significantly increased beyond roughly 120 years, according to the notes.

What is a proposed explanation for the natural limit on human lifespan?

It may be an unintended byproduct of genetic programs that are useful for early-life processes such as development, growth, and reproduction, rather than a program directly selected to cause death.

Why is it difficult to alter one part of the genome to prevent aging?

The genome is interconnected, so changing one component can have multiple side effects elsewhere in the body.

Does the notes' discussion establish one theory of senescence as the only correct explanation?

No. The notes caution against treating antagonistic pleiotropy as definitively superior to mutation accumulation; evidence may support both processes.

What is the social challenge created by an aging population?

Societies must adapt to more older adults and support their health, participation, and roles in society.

What is the International Day of Older Persons intended to highlight, according to the notes?

The role of older people in society.

What is the broad evolutionary explanation for human senescence in the notes?

Senescence may result from the accumulation of harmful mutations or from antagonistic pleiotropy, in which early-life benefits come with late-life costs.

What is an evolutionary mismatch?

A situation in which traits that evolved under ancestral conditions interact poorly with modern environments.

Why are obesity and type 2 diabetes discussed as mismatch-related conditions?

Modern environments make energy-dense foods easier to obtain and often involve less physical activity than ancestral environments, while human appetites and biology reflect older conditions.

What kinds of foods are described as especially easy to obtain in modern environments?

Fatty and sugary foods.

Why might humans be drawn to fatty and sugary foods?

Such preferences could have been useful when energy-rich foods were less available, but they can contribute to health problems when those foods are constantly accessible.

What trend in global obesity is described in the notes?

The notes state that the global rate of obesity has doubled since 1980.

What trend in childhood overweight is described in the notes?

Childhood overweight has increased, including a doubling in the number of overweight children over about 25 years in Africa, according to the notes.

What health problems in children are associated with obesity in the notes?

Breathing difficulties, fractures, hypertension, early markers of cardiovascular disease, insulin resistance, and psychological effects.

What social and psychological difficulties can children with obesity experience?

Bullying and stigma can affect psychological well-being, even as obesity becomes more common.

What is BMI?

Body mass index, a measure used to categorize weight relative to height.

What BMI ranges are listed in the notes?

The notes list 18.5â€"25 as the normal range, below 18.5 as underweight, and above 30 as obese. They also list 25â€"30 as overweight.

What is one limitation of BMI?

BMI is a screening measure and does not directly describe how much body fat a person has or where that fat is distributed; it should not be treated as a complete measure of health.

What are the two types of body fat mentioned in the notes?

Subcutaneous fat, located under the skin, and visceral fat, which accumulates around internal organs.

Why is visceral fat a concern?

Fat accumulated around internal organs can be particularly harmful from a health perspective, even when it is not obvious from appearance.

Is obesity simply an age-related condition?

No. The notes emphasize that obesity has increased across adult age groups and is not simply a consequence of getting older.

What change in adult obesity is mentioned in the notes?

The notes describe an increase of about 10% over 15 years and worsening trends across American groups over roughly 50 years.

What is the thrifty genotype hypothesis?

The hypothesis that ancestral environments favored genetic variants that promoted storing energy as fat when food was available, helping people survive when food later became scarce.

Why might fat storage have been advantageous for ancestors?

Energy stores could help fuel metabolically expensive bodies and brains during periods when food was scarce.

Why is the thrifty genotype hypothesis considered an evolutionary mismatch explanation?

Traits that may have helped ancestors survive food shortages can contribute to obesity when modern environments provide abundant calorie-dense food.

Have the genes responsible for the thrifty genotype hypothesis been clearly identified, according to the notes?

The notes state that the genes responsible have not been identified.

What is the thrifty phenotype hypothesis?

The hypothesis that the environment during gestation can influence how a fetus develops and its later risk of obesity and metabolic disease.

How does the thrifty phenotype hypothesis differ from the thrifty genotype hypothesis?

Thrifty genotype focuses on inherited alleles favored by ancestral conditions; thrifty phenotype focuses on developmental effects of the environment during gestation and their later-life consequences.

What is epigenetics according to the notes?

Inherited or developmental influences that are not encoded directly in the DNA sequence letters A, C, G, and T, and that can affect how genes are switched on or off.

How can a mother's environment affect a developing fetus through epigenetics?

Conditions during gestation can influence gene activity and development, potentially affecting the child's health across the lifespan.

What is the proposed thrifty phenotype mismatch?

A fetus exposed to low nutrient availability may develop in ways suited to scarcity, but later face a calorie-rich environment, increasing the risk of obesity and metabolic disease.

Why might babies exposed to poor maternal nutrition be at greater risk of metabolic syndrome later?

The thrifty phenotype hypothesis proposes that their development may adapt to a low-nutrient environment, leaving them less suited to abundant calories later in life.

What connection between birth weight and later metabolic disease is described in the notes?

The notes state that babies born at low birth weights, often associated with insufficient maternal nutrition, are more likely to develop obesity and metabolic syndrome than babies born at normal or high birth weights.

What historical example is used to discuss prenatal famine and later disease?

The Dutch famine near the end of World War II; the notes say children exposed to famine in the womb had higher rates of diabetes and cardiovascular disease than children born earlier or later.

What does the thrifty phenotype hypothesis not explain fully?

It does not explain why every person who develops obesity does so, since obesity has multiple contributing factors.

What is type 2 diabetes?

A form of diabetes that develops during life and is commonly associated with insulin resistance or insufficient insulin; the notes contrast it with type 1 diabetes.

How does type 2 diabetes differ from type 1 diabetes in the notes?

Type 2 diabetes is described as acquired during life, though it is increasingly diagnosed in younger people. Type 1 diabetes is described as lifelong and present from early life; the notes state it accounts for about 5% of diabetes worldwide.

What is insulin resistance?

A condition in which cells, including fat and muscle cells, do not respond properly to insulin.

What is hyperglycemia?

Higher-than-normal blood sugar.

Why do people with diabetes need to monitor blood sugar?

To track and manage blood sugar levels and reduce the risk of complications.

How can untreated diabetes damage the body?

High blood sugar can damage organs and blood vessels, contribute to narrowed vessels and high blood pressure, and cause eye, kidney, and nerve damage.

What can happen if diabetes-related damage becomes severe?

It can contribute to organ failure and reduced blood flow to the extremities and can be fatal.

How does the thrifty phenotype hypothesis connect to type 2 diabetes?

A fetus adapted to low nutrient availability may be less well suited to a calorie-rich environment later, potentially increasing insulin resistance and type 2 diabetes risk.