Final answer:
The referred phenomenon is the 'Healthy Immigrant Effect,' a population-level finding that shows immigrants often have better health outcomes than their U.S.-born counterparts.
Step-by-step explanation:
The phenomenon being described, where settlers report better physical and mental health outcomes compared to their U.S.-born peers, is commonly referred to as the Healthy Immigrant Effect. This effect highlights how immigrant populations often showcase better well-being and health after arrival in a new country, compared to native residents. This may be attributed to selective migration where individuals self-select for traits that enable them to succeed in new environments, influencing this positive health trend among immigrants.
Additionally, the Founder Effect in human populations, such as the specific case of the Amish, exemplifies how a small group of immigrants can carry certain genetic traits that become prevalent within the isolated community. The Healthy Immigrant Effect, however, is much broader, encompassing not only the genetic but also social, psychological, and environmental facets influencing the immigrant experience and their health outcomes in the host nation.