Glenn, this image haunts me! Since I first laid eyes on it a couple of hours ago, I have not been able to write what I feel.
First of all, converting this to B&W definitely adds to the sadness that I feel. The despair and loneliness of animals being locked up in zoo's. Yes, I know that for some species, it is vital that they are protected. I think it also depends on the type of zoo where they are kept - if it only has the bare cage and bars, then I think it is very cruel.
Regarding the actual animals in your image. There is such a sweet and tender touch between them all. The little one nursing on his momma, and her hand gently laying on top of his head portrays the love and protection she feels for her child. The one full breast, the other one sucked dry ... to me it portrays the process of living and feeding.
The other couple ... to me it looks like an older female, comforting and cuddling a youngster in the group. I am not sure if it is her child, because her teats does not look as if it had milk for a while. Once again you captured the protective hand ... gentle, yet protecting. The expression on the child's face is priceless. To me it seems like absolute content. He knows he is safe and loved.
As for the technical quality of the image - I'm afraid I am much too much of an amateur to give you my input. But will leave you with this ... your image is powerful. Whether one wants to see it as cruelty to animals (for keeping them in zoo's) or whether wants to rather concentrate on the love and community aspect of the primates ... it depends on the viewer.
For me ... this is an image that I am taking to my favourites folder, and thank you for bringing this to me.