Yes, AFFINITIES is a Scrabble word!

Letter values in Scrabble US: A 1, F 4, F 4, I 1, N 1, I 1, T 1, I 1, E 1, S 1.

Is it a valid word?

AFFINITIES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(immunology) the attraction between an antigen and an antibody
(anthropology) kinship by marriage or adoption; not a blood relationship
(biology) state of relationship between organisms or groups of organisms resulting in resemblance in structure or structural parts
a close connection marked by community of interests or similarity in nature or character
the force attracting atoms to each other and binding them together in a molecule
inherent resemblance between persons or things
a natural attraction or feeling of kinship

Also: phylogenetic relation, chemical attraction.