Notes on the Biology of Aging and Theories of Aging

This week's sessions focus on:
- Metabolic rates and body size
- Thermoregulation
- Life history evolution (scholarly context in reproduction and aging)
Current session emphasizes the biology of aging, exploring:
- Why and how we age

Understand concepts of aging including:
- Definition of aging
- Intrinsic and extrinsic drivers of aging
- Diversity in aging patterns across taxa (various species)
- Main evolutionary theories explaining aging

Aging can be defined simply as:
- Decline in biological function over time, leading to eventual death.
More complex definitions exist involving:
- Increasing mortality and decreasing reproductive success as one ages.
Note:
- Aging is often synonymous with senescence in literature regarding population aging.
- In cell biology, senescence refers to cells that stop dividing.

Aging occurs despite environmental stresses, indicating:
- Genes influence patterns of reproduction and body maintenance.
- Aging is a combination of these genetic predispositions and environmental conditions.

Death can arise from various hazards, including:
- Predation, accidents, disease, starvation, extreme temperatures.
Extrinsic factors can affect aging by:
- Accelerating or decelerating aging processes based on lifestyle and environmental pollution in humans.

Key points regarding extrinsic factors for humans:
- Lifestyle choices (exercise, diet)
- Avoiding harmful substances (bad diet, drugs, smoking)
- Difficult-to-avoid environmental pollutants.

Environmental temperature significantly impacts aging rates:
- Chronic heat shortens lifespan, while chronic cool extends it.
- Acute heat shock can extend lifespan due to heat shock proteins that protect against stress.

Dietary restriction is an evolutionary conserved factor that mediates lifespan, with implications spanning several species.
Evidence indicates that:
- Reduced caloric intake (without starvation) leads to extended lifespans in species like mice, worms, and humans.
Visual data shows clear links between caloric intake and lifespan in model organisms like mice.
Points to remember:
- Caloric intake of 85, 50, and 40 calories a week showed longer lifespans compared to fully fed counterparts.
- Research on rhesus macaques supports findings related to lifespan with caloric restriction.

The relationship between reproduction and survival resources is crucial:
- Restricting diets reallocates resources from reproduction to body maintenance, influencing longevity.
- However, balancing reproduction and longevity can vary significantly by species.
Present day dietary habits suggest challenges for adhering to caloric restrictions due to societal issues like obesity.

Aging patterns show variation across species, including:
- Human aging shown via example of performance decline in 5km world records and skin wrinkle density.
Aging patterns highlight the balance of genetic and environmental interactions.

Key theories include:
- Mutation Accumulation
- Antagonistic Pleiotropy
- Disposable Soma
- Hyperfunction theory (modern understanding)

Suggests that natural selection's effectiveness declines with age, allowing deleterious mutations to accumulate post-reproductive age.

Gene mutations may have beneficial effects early in life but negative impacts later, contributing to aging.

Emphasizes resource allocation favoring reproduction over body repair, leading to faster aging processes.

Proposes aging is linked to continued growth and development processes that override the necessary decline, resulting in aging-related diseases.

Aging processes vary by species and depend heavily on environmental and lifestyle factors.
Understanding aging requires considering evolutionary history and modern living conditions.

Resources available on course portal (Canvas) for further study and exam preparation.