History, by my reading, seems more replete with examples of extended families, which include additional relatives like grandparents, aunts, and uncles.

eg:

  Some sociologists and anthropologists consider the extended family structure to be the most common family structure in most cultures and at most times for humans, rather than the nuclear family.

which also provides the common use definitions:

  A nuclear family (also known as an elementary family, atomic family, or conjugal family) is a term for a family group consisting of parents and their children (one or more), typically living in one home residence.

  It is in contrast to a single-parent family, a larger extended family, or a family with more than two parents.

  Contemporary trends such as increased one-parent families, high divorce rates, second marriages and homosexual partnerships have all contributed to variations in the traditional family structure.

  But to what degree has the function of the family changed and how have these changes affected family roles in cultures throughout the world? This book attempts to answer these questions through a psychological study of families in thirty nations, carefully selected to present a diverse cultural mix.

  The study utilises both cross-cultural and indigenous perspectives to analyse variables including family networks, family roles, emotional bonds, personality traits, self-construal, and 'family portraits' in which the authors address common core themes of the family as they apply to their native countries.

  From the introductory history of the study of the family to the concluding indigenous psychological analysis of the family, this book is a source for students and researchers in psychology, sociology and anthropology.

I can't access the first source for that Wikipedia quote, but the second is a defunct website created by a graduate student. The fact that they're using it in the introduction for an article about the nuclear family is a good reason why people should be skeptical about claims on Wikipedia and should look into the sources themselves, not treat Wikipedia as if it was a source.

Isn't the extended family just a superset of the nuclear (or atomic) family? Defining the boundaries at grand-parents, aunts and uncles (I'm guessing proximity-based living relatives is kind of where you're making the boundary). By that logic an extended family is a nuclear family (formally) as it contains the definition of nuclear families by default, the nuclear family is just the smallest self replicating unit we've got available by default. Sperm (differential change between gens), (egg - really mitochondria) consistent base stability (ground truth) across gens, and the ability to self replicate.

EDIT: If you're arguing mixture of experts works better, than sure, I got you, if your arguing that there's a more non-binary way to do the self replication, that's a harder road to hoe. At least if you want to do it for free, which has a better track record of working for most people.

See my other comment in this thread about anthropologists dichotomizing societies based on nuclear vs extended families. In short, it’s orthogonal to the issue.