Senescence — 2020 Paper I

Approach

• Demand of Question: Explain senescence as biological ageing and discuss its major physiological and evolutionary dimensions.
• Structuring the Response: Define senescence, outline major age-related changes and theories, and distinguish it from chronological ageing.
• Key Dimensions to Cover: Cellular ageing, homeostasis, telomeres, oxidative damage, mutation accumulation, antagonistic pleiotropy and disposable soma theory.

Model Answer

Introduction

Senescence is the progressive decline in physiological function and biological resilience with advancing age, leading to reduced capacity to maintain homeostasis and increasing vulnerability to disease and mortality. It is a biological process and should not be equated simply with chronological age.

Major manifestations

Senescence involves gradual changes in:

• muscular strength and bone density;
• immune competence;
• cardiovascular efficiency;
• reproductive function;
• sensory capacity;
• tissue repair and recovery.

At the cellular level, ageing is associated with:

• accumulation of molecular damage;
• cellular senescence;
• altered mitochondrial function;
• changes in telomere dynamics;
• reduced regenerative capacity.

Evolutionary explanations

1. Mutation accumulation — Peter Medawar: Harmful mutations expressed mainly at older ages are weakly removed by natural selection.
2. Antagonistic pleiotropy — George C. Williams: Genes beneficial early in life may have detrimental effects later.
3. Disposable soma theory — Thomas Kirkwood: Organisms allocate limited energy between reproduction and long-term somatic maintenance.

Thus:

Limited maintenance → Accumulated damage → Functional decline → Senescence

Biocultural dimension

Human ageing varies with:

• nutrition;
• disease exposure;
• physical activity;
• occupation;
• socioeconomic environment.

Conclusion

Senescence is therefore a biological and biocultural process, resulting from evolutionary trade-offs interacting with environmental and lifestyle conditions across the life course.