They were only concerned for the members of the "Aryan" race. The sufferings of anyone else simply did not matter to them. If special consideration is not given to any certain race or sex, then why should it be given to any certain species? Under this principle, everything is irrelevant except for the interest themselves. If non-human animals were left out of the principle that would be going against the principle itself. Simply because some people are not members of out race does not entitle us to exploit them (Singer 56). This also holds for non-humans, the fact that other animals are less intelligent than we are doesn't mean that their interests may be disregarded (Singer 56). Singer makes an excellent point when he specifies that the characteristic entitling a being to equal consideration is the capacity for suffering. This is true and can be seen in his next example. It would be nonsense to say that it was not in the interest of a stone to be kicked along the road by a schoolboy (Singer 57). If the sentence was re-worded and a mouse was being kicked along the road, it auld be quite obvious that those were not in its interests. .
Of the various objections about the equality of animals under the equal considerations principle, I feel that the most important one questions why humans shouldn't eat animals, if animals eat each other. Singer also describes this as the Benjamin Franklin Objection. When Franklin's friends were preparing to fry a fish, it was cut open and a smaller fish was found inside of its stomach. Franklin then figured that if fish eat one another then there is no problem with eating fish at all. When thinking about this objection the theory of the "survival of the fittest" comes to mind. Singer shoots down this argument by explaining that if we hunted for food and actually captured that animal, then that could be called "survival of the fittest". Since we do not hunt and instead we mass produce domestic animals in factory farms, this is not "survival of he fittest".