What is the most likely cause of a new trait such as blue eyes developing in humans?

The emergence of a new trait, such as blue eyes in humans, is primarily attributed to mutation. Mutations are changes in the DNA sequence that can occur spontaneously or due to environmental factors. When a mutation leads to a variation in a trait, such as eye color, it can be passed down to future generations if it occurs in the germ cells (sperm or egg). This genetic change results in a new phenotype within the population.

Mutations are essential for introducing genetic diversity within a species, and in this case, the mutation affecting melanin production in the iris gives rise to blue eyes. This genetic variability is a fundamental mechanism of evolution, as it provides a source for natural selection to act upon, potentially allowing for adaptation to different environmental conditions over time.

Adaptation to new environments refers more to the process by which a species develops characteristics that enhance their survival and reproduction in a specific habitat, rather than the initial cause of a new trait. Acquired characteristics from parents suggest traits developed during an organism's lifetime, which do not get passed on genetically, so this doesn't contribute to the development of blue eyes. Migration of populations can lead to the spread of existing traits among different groups but does not itself create new traits.