Final answer:
People who look alike but aren't related are often called doppelgängers. In biology, analogous features arise in unrelated species due to convergent evolution. The concept of similarity without relation can be mirrored in social categorization, like the term 'Millennials.'
Step-by-step explanation:
The term for people who look alike but aren't related is commonly referred to as doppelgängers. However, this concept can be paralleled in biology by the term analogy or homoplasy, where unrelated organisms appear very much alike because they have evolved under similar environmental constraints, leading to common adaptations.
A good example of this in nature is the way insects, bats, and birds have developed wings; these structures are analogous as they serve the same function but have different embryonic origins and structural make-up, exemplifying convergent evolution.
In the social sciences, people who share characteristics but not necessarily frequent interaction or a sense of group identity are considered to be a category rather than a group. An example provided is Millennials, who are categorized together because they were all born within a specific time period but do not form a cohesive interacting group.