The Colony Genetics
Problem
How many people do you need to start a colony that survives a thousand years?
There is no agreed answer. Only estimates. The most-cited figure for a long-duration space colony is approximately 160 founders, based on work by anthropologist John H. Moore. Other models range from 98 to over 10,000. The answer depends on what you are trying to preserve: bare survival, genetic diversity, cultural complexity, or species-level robustness. This is the genetic side of the continuity question.
The Estimates
Proposed minimum viable populations vary by two orders of magnitude. Each one measures something different.
// Bar lengths are logarithmic. The accent bar is the figure most cited in the literature on long-duration crewed missions.
The Population Pyramid
A population pyramid is more useful than a head count. Move the slider and watch how the demographic profile evolves a century later.
The Founder Effect
Genetic diversity erodes each generation in a closed population. The smaller the founder group, the steeper the curve.
The Founder Couples Math
Five generations of arithmetic: births, survival, and pairing. The cohort drifts off the mean fast.
// Assumes 2.1 children per couple, 95% survival to reproductive age, balanced sex ratio. Real cohorts diverge from these means quickly.
The Hard Realities
The math above assumes a controlled population in a stable environment. None of those assumptions hold in space.
Radiation exposure
Cosmic rays and solar events damage germline DNA. Mutation load rises generationally.
Fetal development in low gravity
No human pregnancy has been completed off-Earth. Animal data is suggestive and worrying.
Sex-ratio drift
Random sampling in small cohorts produces uneven ratios. A 60/40 split halves effective N.
Skill loss across generations
Founders are screened experts. Their grandchildren learn from books and each other.
Cultural drift
Languages, norms and goals diverge from origin. By Gen 5 the "mission" may not mean the same thing.
Recessive disease alleles
A single founder carrier seeds the entire downstream population. Screening is imperfect.
Mate selection
Small isolated populations have few choices. Pairing must be planned, not chosen, to preserve N_e.
Compounding effects
All of the above interact. The combined effect is not modeled by any current dataset.
Is 160 enough?
Probably enough to survive. Probably not enough for what most people picture when they say "colony." It is the figure most cited in the literature, and the literature is thin. The 150 Human Test uses this number as its starting point.
Cited & consulted
- // Moore, J. H. (2003). "Evaluating Five Models of Human Colonization." American Anthropologist, 105(1).
- // Salmon & Allshouse minimum viable population estimates for isolated cohorts.
- // NASA Human Research Program — radiation, microgravity and reproductive health publications.
- // Standard demographic transition models & conservation-genetics N_e literature.
// Estimates vary across methodologies. Numbers shown are educational, not operational.