What do you mean by environmental factors? The environment drives evolution, so changes in the environment would change who survives, which would lead to evolution. If it is an environmental factor that led to selection of individuals having this vein being more likely to propagate, that would still be evolution. This also some very simple scenarios that could lead to such a pressure, like the artery having some minor benefit in reproduction, but a disease we eradicated would disproportionately kill people with the artery.