How does the absence of women affect the plot and theme of The Road?

Well, women are not completely absent from The
Road, although the female characters are temporary and tragic.  There is the
argument flashback between the father and mother, where the mother has decided to take
her life rather than face the reality of the post-apocalypse world.  Her decision, and
her absence from the book is a major theme: the absence of hope, the absence of future. 
Most of the other women in the book are horrible victims, those held captive and bred
for food, which simply reinforces McCarthy's theme of
hopelessness.

Only at the very end of the story does he
give a glimpse past the hopelessness, with the woman who embraces the orphaned
boy.