Same way humans were differentiated by using races - ranking us lower&#x2F;higher better&#x2F;worse than others, that&#x27;s what people do with species.<p>If you find the theory of evolution a fact, then you wouldn&#x27;t laugh at me. Any rational evolutionary biologist will agree that species are here to simplify the conversations, they cannot be used for ranking which species are better - they are also not the main theme of research.<p>Do you know how species are defined? Sane definition? - members of the same species can produce a fertile offspring. But there are hundreds if not thousand of exceptions where this happens even across the species boundary - the reason why it happens is that our labeling is in its core subjective and somewhat arbitrary, there&#x27;s no dividng line&#x2F;plane&#x2F;svm-hyperplane.<p>In the parallel lines of time in evolution and natural selection we&#x27;ve been as long as all the living beings.<p>You wouldn&#x27;t find homo erectus (neanderthalensis, habilis, rudolfensis, ergaster, floresiensis, even some australopithecae) attractive but you could procreate. There&#x27;s a biological reason why you can&#x27;t have children with a horse, it&#x27;s not a species reason, it&#x27;s not even ingrained in our species labeling as can be seen from the above definition.<p>What, you would rank the being as irrelevant (or less relevant) if you can&#x27;t have children with it? Comedy of irrationality.<p>Go try finding your rationality and get back to us on that.