How can studies of animal behaviour and reactions be applied to human psychology?

Most animal experiments are conducted by psychiatrists and psychologists, and they almost always never reach a conclusion after conducting them; Henry Harlow, Vincent Dole, etc.

Despite decades of cruel and painful experiments, many psychologists criticize the field for producing little scientific benefit. Animals are experimentally manipulated in ways that would be ethically unacceptable in humans, yet this results in artificially-induced conditions that correspond only superficially to the naturally occurring human condition. In attempting to discover the inner workings of the human mind, psychology researchers ultimately lose sight of the inherent value of an animal's own consciousness.

Studying humans would seem a lot more efficient, wouldn't it?