The socioeconomic demands of the present and the threatened socioeconomic demands of the future have led the American woman to displace, or threaten to displace, the American man in science and industry.
I think this is referring to the (future) women's rights movements and the push for women to be more of a worker, rather than a mother. This is HIGHLY controversial so I will try to choose my words wisely. To me, this article points out that someone (mother or father) needs to be there to love (provide comfort and warmth) to babies. And if a woman wants to be the bread winner, be at work more than at home, and have a partner (man or woman) be at home taking care of the baby, her income needs to be great enough to support the partner at home as well. When both partners work and cannot provide the baby's love needs, the baby could struggle to develop positively. All I am really trying to say here is that we, as Americans, need to find a way that one partner can work and it be enough to provide for our families; for our children's sake. It is very insightful that Harlow noticed this fact in 1958.