Nah. If that were their primary function, they'd be like chimp teats, which look like BOTTLES THAT YOU USE TO FEED CHILDREN.
breasts are a gender marker, sure. they're used to feed infants
They are an evolutionary adaptation to being bi-pedal, because males used to only have an ass to look at and assess, and upright, face-to-face women developed a surrogate pair of ass-lobes to recapture our fleeting attention.
"Ah, those endless forests, and their horror-haunted gloom! For what eternities have I wandered through them, a timid, hunted creature, starting at the least sound, frightened of my own shadow, keyed-up, ever alert and vigilant, ready on the instant to dash away in mad flight for my life. For I was the prey of all manner of fierce life that dwelt in the forest, and it was in ecstasies of fear that I fled before the hunting monsters."
Jack london, "Before Adam"