In a precedent-setting case, PETA US, three marine-mammal experts and two former orca trainers are suing SeaWorld on behalf of five orcas who were taken from their home by force, locked up, put to work and never allowed to leave. The case intends to prove that these orcas are being held as slaves in violation of the 13th Amendment to the US Constitution. The suit is one of the most groundbreaking legal cases ever to reach the courts - the first ever to assert that a constitutional right should extend to nonhuman animals.

In the not-too-distant past, newspapers vigorously editorialised in opposition to extending to women the right to own property, gain custody of their children or vote. "What's next?" they wrote, "The right of asses to vote?" The idea of women attending medical school was similarly denounced with bold statements asserting that these "frail creatures" would "faint at the sight of blood." Black men and women were declared "subhuman" and "lacking in the emotions, senses and morals of white people," and those who fought for their rights often found themselves attacked not only in print but also by enraged supremacists.

We can be ashamed of our past shortsightedness and bigotry, but to fail to examine our present treatment of those we see as "different" is to put at risk our society's moral evolution. Our current challenge is to put history's lessons to work today, and PETA US' lawsuit can and will do just that.

Orcas in the wild lead rich, complex lives. They are intelligent animals who work cooperatively, form close relationships, communicate using distinct dialects and swim up to 100 miles every day. Orcas at SeaWorld are forced to toil day after day, repeating the same endless tasks with no choice in the matter and no escape. They have been turned into perpetual breeding machines to provide more performers for SeaWorld's cruel shows.

Attorneys will ask for Tilikum, Katina, Kasatka, Ulises and Corky to be released into a more appropriate environment, such as a coastal sanctuary. Protected sea pens would allow these orcas greater freedom of movement; the ability to see, sense and communicate with their wild cousins and other ocean animals; and the ability to feel the tides and waves and engage in the types of behaviour that define who they are.

Our understanding of animals expands every day. Animals are no longer regarded as "things" to dominate but as breathing, feeling beings with families, intellect and emotions. The UK was the first country in the world to introduce an animal welfare law to prevent the cruel treatment of cattle in 1882, and the European Union officially recognised animals as sentient beings back in 1997. What we should really be asking ourselves is this: why is it taking so long for animals to gain legally recognised rights? Just as we look back with shame at a time when humans were viewed by some as property and less deserving of protection and consideration, we will look back with shame on our current treatment of animals.

Follow Mimi Bekhechi on Twitter: www.twitter.com/@Mimi_Bekhechi