There's a difference between having moral worth and being a moral agent. Non-human animals (generally) cannot contemplate the ethical character of their actions, so they are not moral agents, nor should we consider them such. This does not mean they are unworthy of moral consideration. What is being evaluated is the ethics of the behavior of people who are moral agents, and there have been guide sticks for the behavior of people for as long as people have been thinking about ethics.
There's a difference between having moral worth and being a moral agent. Non-human animals (generally) cannot contemplate the ethical character of their actions, so they are not moral agents, nor should we consider them such. This does not mean they are unworthy of moral consideration. What is being evaluated is the ethics of the behavior of people who are moral agents, and there have been guide sticks for the behavior of people for as long as people have been thinking about ethics.