Anything can serve as moral authority. The question is what morals do you want to live under. Nature promotes the survival of the fittest. There rarely is a family unit and even if there is helping someone outside your cirlce is unheard of. There is no wellfare, if you can't provide in any way you die. There is no such thing as rape. No one cares about murder its actually expected. You have no rights to anything. If you can't fight for it and win its not yours. Also the idea would force humans to except they are no special case from nature. I dnt see that happening either XD
Nature offers no moral authority whatsoever on account of the fact that one cannot derive an ought from an is. That is to say, we can look around us all we like to see the way things are, but in doing so we can never find something which authoritatively suggests how things ought to be.
Nature does not take a moral stance if an organism (humans) breed to the point of starvation and death. The physical world sets limits. Nature doesn't respond to or 'think' in terms of right and wrong. Nature doesn't care whether humans exist or do not exist. It simply has the capability to respond in an undesirable or indifferent fashion towards human objectives and desires. Nature provides the final judgement, but that judgement is not based on human morality; it is indifferent. It simply seeks its own state of balance.