Full Idea
Kinship is essentialized, but admits of degrees, ...and people can be essentialist even about categories they do not view as fixed over time, such as age groupings.
Gist of Idea
Kinship is essence that comes in degrees, and age groups are essences that change over time
Source
Susan A. Gelman (The Essential Child [2003], 03 'Summary')
Book Reference
Gelman,Susan A.: 'The Essential Child' [OUP 2005], p.88
A Reaction
Given my notion of essence are necessarily explanatory, I embrace both of these points. Being very athletic comes in degrees, and changes over times.