The small, non-representative group of initial colonists will create a genetic bottleneck. Their specific genetic makeup will have an outsized influence on all subsequent generations born on Mars, leading to rapid evolutionary change and reduced overall genetic diversity compared to Earth's population.

Species from different branches of the tree of life often independently develop similar traits to solve the same problem, like swallows and swifts evolving for aerial insect hunting. This 'convergent evolution' makes them appear closely related, posing a significant challenge to accurately mapping evolutionary history.

Contrary to the idea of linear progress, human evolution has had detrimental effects on our health. Over centuries, our mouths have grown smaller, leaving insufficient room for teeth to grow straight and constricting our airways. This is a primary cause of modern afflictions like sleep apnea, snoring, and asthma.

Natural selection often favors traits that maximize reproductive fitness, even if it pushes them to a dangerous peak where a small step further leads to catastrophic failure. This "cliff edge" model helps explain disorders like schizophrenia or childbirth complications, where genes beneficial in moderation can be disastrous in excess.

Living in a sterile Martian habitat, colonists would only be exposed to a tiny fraction of Earth's microbes. Their immune systems would be unprepared for Earth's vast microbial diversity, making a return journey potentially fatal. This creates a permanent biological quarantine that would accelerate human speciation.

A human born and raised in Mars's one-third gravity would likely not develop the bone density and muscular strength required to withstand Earth's gravity. The physical stress would be painful and potentially debilitating, effectively trapping them on their home planet for life.

To shield against radiation and meteorites, Martian habitats will likely be built underground, not in glass domes. A society that lives its entire existence underground, reliant on artificial light and disconnected from an open sky, would develop a psychology profoundly different from Earth's.

The Inca civilization developed in extreme isolation, protected by the Andes, the Amazon, and the Pacific. This allowed for the growth of a unique society. However, this same isolation proved fatal, as it meant they had no immunity to Old World diseases like smallpox and no conceptual framework for dealing with outsiders.

Women raised in one-third gravity may have bones too brittle for natural childbirth, risking fatal pelvic fractures. If C-sections become the norm, the evolutionary pressure that limits a baby's head size to fit the birth canal is removed. This could lead to the rapid evolution of larger-headed humans.