Science is unable to discover any major difference between human beings and animals, outside of what they consider to be "cognitive abilities." These abilities are defined as the process of thought and the communication of thoughts. Studies have proven that we all experience pain, pleasure, fear, contentment, anxiety, sense of loss, and most importantly...love, and the ability to form emotional bonds with others.
Animals lack human speech, instead relying on sounds, pheromones, and physical displays to convey messages. Is this not communication of thoughts? Human babies and those with disabilities also lack skills in conventional speech. Are they less than human? Perhaps human beings are the ones deficient in skills to discern the meaning of the languages of other species.
Self awareness: Literally, a sense of self. "This is me, and this is mine." Possessiveness and social hierarchy indicate they are endowed with sense of self.
The concept of past, present, and future: Many human beings have no grasp of history, and were it not for photos, drawings, and tales related to them of their childhood, would have no memory or concept of their past. No one has been scientifically proven to remember their own infancy. Animals have been shown to still grieve for others long since departed, evidence of a concept of past and current state of loss. Animals are aware of their present state of being, as evidenced by satisfying their current needs regarding hunger, thirst, shelter, and companionship. They actively prepare for the future in terms of caching meals for later use, digging dens in preparation for inclement weather, or motherhood.
Throughout history mankind has denigrated and devalued others to justify his use and abuse of others, as evidenced by slavery and the subjection of women. If animals were endowed with the same rights as humans there would be no justifiable slaughter and laboratory use of them. Human beings are still primitive and sacrificing others in the name of a higher power...the pseudoscience of man's superiority.
Animal and human rights should be one and the same. A truly intelligent being would comprehend this.