Lesson 5

Question 1

Why do organisms die

Answer 1

Proximate (mechanistic) causes:
- Extrinsic factors: Accidents, disease, environmental threats.
- Intrinsic factors: Cellular senescence, programmed aging, genetic factors.
- Senescence: Decline in reproductive potential and increased mortality with age.
- Apoptosis: Programmed cell death.
- Hayflick Limit: Cells have a finite capacity to divide before they die.
- Telomeres: DNA caps that shorten with each cell division, limiting lifespan.

Question 2

Why do organisms die (ultimate/evolutionary) causes

Answer 2

Disposable Soma Theory: Organisms allocate energy to reproduction over long-term maintenance.

Mutation Accumulation Theory (Medawar): Harmful mutations manifest later in life and are not strongly selected against.

Antagonistic Pleiotropy (Williams): Genes beneficial early in life may be detrimental later (e.g., high fertility early, cancer risk later).

Question 3

Why cant we live forever?

Answer 3

Telomeres are protective caps of DNA and protein structures found at the ends of chromosomes, playing a crucial role in preserving genomic integrity, regulating cell division, and potentially influencing aging and cancer development.

Telomeres shorten with age, causing replication issues. Telomerase is an enzyme that can extend telomeres; active in cancer cells, allowing uncontrolled division.

Question 4

P53 gene

Answer 4

Regulates telomerase, protecting against cancer.

High levels cause tissue aging, low levels increase cancer risk.

Represents a tradeoff between longevity and cancer resistance.

Question 5

Apoptosis

Answer 5

Programmed cell death

Question 6

Smoking and aging and senescence

Answer 6

• chemicals within cigarette smoke directly reduce telomere length

This has two implications, by:
- Identifying the mechanism for premature aging
known among smokers
- providing further evidence for a direct link
between smoking and cell replication (Cancer)

Question 8

Cell senescence and Covid

Answer 8

• There are now many lines of evidence that severe Covid-19 infections influence cellular inflammation and aging
• Senescent cells damage function can lead to death in elderly
• Shorter telomeres, more susceptible to tissue damage

Question 9

Disposable soma theory

Answer 9

cell maintenance is costly (non-genetic)
With extrinsic mortality high in the wild, it is
wasteful to use metabolic resources to maintain the
body beyond the expected lifespan
Using energy to increase reproductive capacity is
more beneficial from an evolutionary standpoint
the body is like a disposable product, only designed
to last as long as necessary.
Species with higher extrinsic mortality expend less
energy on cell maintenance = shorter lifespans

Question 10

Accumulated mutations theory

Answer 10

the influence of natural selection decreases with age.

Mutations that do not manifest themselves until late in life will not be subject to selection

Therefore, mutations accumulate with age, and damage cell function

Question 11

Antagonistic Pleiotropy theory

Answer 11

• Genes exist which are beneficial in early life, but have harmful effects in later life

If the genes confer reproductive advantage, they will be selected for, despite “trade off”

“live fast, die young” – faster reproducing animals live shorter lifespans

Question 12

Modern mortality patterns

Answer 12

Cultural and socioeconomic factors strongly affect mortality:

• Wealth correlates with lower mortality.
• Gender differences: Female mortality generally lower.
• Global variation in death causes reflects different social and healthcare contexts.