Our analysis must not be misinterpreted as an attempt to champion altruism in relation to animals. It merely reaffirms the principle of justice. That is why there can be no general philosophical injunction that we subordinate our interests to those of animals under any circumstances. Each time we are confronted with a conflict between our own and an animal's interest, we must decide, after making fair allowance for each, which of the two interests deserves to be given preference. Thus it may well be permitted to injure an animal's interest in order to avoid injuring a preponderant interest of our own; but at the same time a limit is set to the extent of the injury, which is permitted only under condition that an actual conflict is involved—this must be proved separately in each case. After such proof has been supplied, we must ask further on which side lies the preponderant interest. In no event is it permissible to regard the animal's interest as inferior without good reason, and to proceed to injure it.
(Leonard Nelson, System of Ethics, trans. Norbert Guterman [New Haven: Yale University Press, 1956], 142 [first published in German in 1932])