Cowbirds:

As with any species there are also birds of lessor qualities like the cowbird. Consider that the cowbird during nesting time will look for a nest, wait until the host leaves for a few minutes and then will lay its egg in the nest and let the host bird hatch it. The cowbird will take out one of the host birds eggs to replace it with her own.

The unsuspecting host then raises the chick along with its own. Sometimes the cowbird chick, because it is larger, will force the host birds chick out of the nest to make more room for itself. Consider human society as it exists today and see if any comparisons can be made between the cowbird characteristics and human characteristics.