Answer: objects in a category have a family resemblance to one another
Step-by-step explanation:
The TYPICALITY EFFECT explains why humans have a tendency to classify objects in a category due to that object sharing characteristics with other members in that category as opposed to the members of that category that do not.
In other words, we classify TYPICAL members of a group as being in that group as opposed to ATYPICAL members of that group.
For example, categorizing a DOG as a MAMMAL is a no brainier but classifying a WHALE as a MAMMAL will meet some resistance even though they are.