Mice (Mus Musculus)

Mice are often used in scientific research because they share many genetic and physical traits with humans. However, since mice and humans evolved in different environments, they have distinct differences. While both species have certain shared biological processes, their reactions to experiments can vary significantly. Mice are great for studying shared biological traits and understanding how different species develop from common genes. But when it comes to mimicking human diseases, mice might not always be the best models since the connections between genes and diseases can vary between humans and mice. So, while mice are helpful in research, it's essential to consider both their similarities and differences with humans.

Benefits for Longevity Research

Mice are beneficial for longevity research for several reasons:

1. Short Lifespan: Mice have a relatively short lifespan, typically 2-3 years. This allows researchers to study the entire life cycle of the organism in a condensed time frame, making it feasible to observe the effects of interventions on aging within a realistic research period.
2. Genetic Manipulability: Mice genomes can be easily manipulated, allowing scientists to create genetically modified strains to study specific genes or pathways related to aging.
3. Conserved Aging Mechanisms: Many biological processes related to aging are conserved between mice and humans. This means that discoveries in mice often provide insights into human aging and potential interventions.
4. Cost-Effective: Maintaining mice in a research setting is less expensive compared to larger animals. This makes it economically feasible to run long-term studies with large sample sizes.
5. Reproducibility: Mice have relatively short reproductive cycles and produce numerous offspring. This allows for studies across multiple generations in a short time.
6. Controlled Environment: It's easier to control external factors such as diet, environment, and exposure to substances in mice, ensuring that the observed effects are due to the interventions and not external variables.
7. Rich Data Sets: Due to the extensive use of mice in research, there's a wealth of pre-existing data available. This enables researchers to compare and contrast findings from longevity studies with data from other domains.
8. Ethical Considerations: While all animal research has ethical considerations, the use of shorter-lived organisms like mice often presents fewer ethical complexities than the use of longer-lived animals, especially primates.

Differences Between Human and Laboratory Mice

Feature	Mice	Human	Difference
Lifespan	~2-3 years	~80 years (average)	~40x
Reproductive Age Start	~6-8 weeks	~12-15 years	~100x
Growth Rate	2-3 months to maturity	18-25 years to reach full adult size	~90x to ~100x
Genome	~20,000-25,000 protein-coding genes	~20,000-25,000 protein-coding genes	differences in some gene families and pathways
Genome Size	~2.7 billion base pairs	~3.2 billion base pairs
Number of Chromosomes	40 (20 pairs)	46 (23 pairs)
Heart Rate	~500-700 beats/minute	~60-100 beats/minute	~8x
Metabolic Rate	Faster	Slower	Variable (often >10x)
Bone Density Decline	Begins around 1 year	Begins in late 20s	~25x
Body Weight	20-40 g (female) & 25-45 g (male)	Average 62 kg (female) & 77 kg (male)	~2000x (average)
Brain Size	~0.4 cm³	~1400 cm³	~3500x
Blood Volume	~2 ml	~5 liters	~2500x
Caloric Restriction Response	Increases longevity	Increases longevity
Diet	Omnivorous, often fed controlled diets in labs	Omnivorous, varied diet
Telomere Length	Relatively longer in many cells	Shorter in somatic cells
Reproductive Cycle	4-5 days (Estrous cycle)	~28 days (Menstrual cycle)	~6x
Pregnancy Duration	~19-21 days	~280 days	~14x
Immune System	Faster initial response, less memory-driven	Slower response, memory-driven
Drug Metabolism	Faster drug metabolism due to differences in liver enzymes	Slower drug metabolism
Blood Cell Lifespan	Red cells: ~40 days	Red cells: ~120 days	~3x
Allometric Scaling Correction Factor	3	37	~12x

See for relating the ages of men and mice.