Why "mysterious ways" don't matter.

[Esquilax]

I don't have his book, but here is an excerpt from Wikipedia article on Speciesism regarding Richard Dawkins' opposition.

In the chapter "The one true tree of life" in The Blind Watchmaker, he argues that it is not only zoological taxonomy that is saved from awkward ambiguity by the extinction of intermediate forms, but also human ethics and law. Dawkins argues that what he calls the "discontinuous mind" is ubiquitous, dividing the world into units that reflect nothing but our use of language, and animals into discontinuous species:
The director of a zoo is entitled to "put down" a chimpanzee that is surplus to requirements, while any suggestion that he might "put down" a redundant keeper or ticket-seller would be greeted with howls of incredulous outrage. The chimpanzee is the property of the zoo. Humans are nowadays not supposed to be anybody's property, yet the rationale for discriminating against chimpanzees is seldom spelled out, and I doubt if there is a defensible rationale at all. Such is the breathtaking speciesism of our Christian-inspired attitudes, the abortion of a single human zygote (most of them are destined to be spontaneously aborted anyway) can arouse more moral solicitude and righteous indignation than the vivisection of any number of intelligent adult chimpanzees! ... The only reason we can be comfortable with such a double standard is that the intermediates between humans and chimps are all dead.

http://en.wikipedia.org/wiki/Speciesism#...us_mind.22

I tend to agree with this line of argument, which is why I don't partake in animal products- leather and so on- beyond food. There's definitely a hierarchy involved, depending on sentience and cognition (I doubt anyone would mourn a swatted mosquito, as it doesn't have the intelligence to render that wasteful in a moral sense) but there's no need to exhibit unnecessary cruelty or callousness regarding animals. This is somewhat reflected in our legal system, where animal cruelty laws exist.

It's a difficult line to properly quantify, definitely a grey area, but that's not a challenge to human derived morality in itself. It's just an effect of living in a complicated world.