Hippos’ skin tones are either purple-gray or slate, with brownish-pink coloring around their ears and eyes. The inner skin layers are thick; and they have a layer of blubber, like that of their closest relatives, whales. The outer skin layers, however, are very thin.

In the 1980s, Colombian cocaine kingpin and drug trafficker Pablo Escobar purchased four hippopotamuses for his private zoo. After he died in 1993, the Colombian government left the hippos in a pond on his ranch because it was unable to transport them to a suitable environment. In the years that followed, the hippos escaped the property, relocated to the Magdalena River and reproduced at a rate—their numbers have grown to an estimated 80 to 100—that some ecologists consider to be unsustainable.

Some have viewed the hippos as invasive pests that should not run wild in South America. But a new study by an international group of researchers challenges that view.

And, the Escobar hippos have now achieved another milestone: they’ve reached the status of “personhood.”

The Magdalena River runs up the western side of Colombia for almost 1,000 miles. With the fifth-largest river basin in South America, the Magdalena has a fertile valley that supports crops such as cacao, coffee and corn. ©Erik Cleves Kristensen, flickr

What’s the definition of the “natural world”? Introduced species may bring us closer to it.

What most of us think of as the modern “natural world” is very different than it was for the last 45 million years. For example, even recently, rhino-sized, wombat relatives called diprotodons; tanklike, armored glyptodons; and two-story-tall sloths ruled the world. These giant herbivores began their evolutionary rise not long after the demise of the dinosaurs. However, they were abruptly driven extinct beginning about 100,000 years ago, most likely due to hunting and other pressures from our Late Pleistocene ancestors.

While human impacts have caused the extinction of several large mammals over the last 100,000 years, we have since introduced numerous species, inadvertently rewilding many parts of the world, such as South America, where giant llamas once roamed, and North America, where the flat-headed peccary could once be found from New York to California.

Using that knowledge as a premise, the authors of the new study, published in the journal Proceedings of the National Academy of Sciences in the United States of America on April 7, 2020, undertook a worldwide analysis that compared key ecological traits of herbivores (body size, diet and habitats) from before the Late Pleistocene extinctions to introduced species of the present day, such as Escobar’s hippos.


The horses brought over in the 1400s from Spain were not the first horses in North America. Native Americans had long-standing relationships with wild horses that go back thousands of years.

The analysis revealed that such introductions restore many important traits that have been lost for thousands of years. For example, the feral hippos in South America are similar in body size and diet to extinct giant llamas, while a bizarre type of extinct mammal—a notoungulate—shares large size and a semiaquatic habitat with hippos. So, while hippos don’t perfectly replace any one extinct species, they restore parts of important ecologies across several species.

The researchers say this is because 64 percent of introduced herbivores are more like extinct species than local native species. These introduced “surrogates” for extinct species include evolutionarily close species in some places, such as the wild mustangs in North America, where pre-domestic horses of the same species lived but were driven extinct.

What can a broader perspective achieve? An understanding of the role introduced species play.

Many people are concerned about feral horses and donkeys in the American Southwest because they aren’t known to have been on the continent in historic times. But this view overlooks the fact that horses had been present in North America for more than 50 million years; all major events in their evolution, including their origin, took place here. They only disappeared a few thousand years ago because of humans, meaning that the North American ecosystems they have since been reintroduced to had co-evolved with horses for millions of years.


Hippos are the third-largest living land mammal, after elephants and white rhinos. Despite their large and bulky appearance, they have adaptations to their semi-aquatic environments that allow them to move swiftly on both land and water.

So, while we usually think of nature as defined by the short period of time for which we have recorded history, we should realize that this is already long after pervasive and strong human influences. Broadening our perspective to look beyond the past few hundred years—to a time before widespread, human-caused, prehistoric extinctions—to include the evolutionarily relevant past lets us ask more nuanced questions about introduced species and how they affect the world.

The authors of the study conclude that, strangely enough, by introducing species across the globe, humans restored lost ecological traits to many ecosystems, making the world more like the Late Pleistocene, bringing broader biodiversity benefits and counteracting a legacy of extinctions.

Who is a “legal person”? For the first time in a U.S. court, hippos.

Not only have Pablo Escobar’s hippos prompted research into what, exactly, a natural habitat is, they have now inspired an advance in the animal-personhood movement.


A hippo’s powerful jaws can open to 150 degrees, revealing their enormous incisors.

Just about a month ago, on October 20, 2021, the Animal Legal Defense Fund announced that the U.S. District Court for the Southern District of Ohio has recognized animals as legal persons for the first time in the United States.

In pursuit of deposing two wildlife experts with expertise in nonsurgical sterilization who reside in Ohio, the Animal Legal Defense Fund filed an application on behalf of the plaintiffs—the “community of hippopotamuses living in the Magdalena River”—in a Colombian lawsuit against the country’s government regarding a plan to kill roughly 100 hippos who are descendants of animals imported by Pablo Escobar.

In Colombia, animals have standing to bring lawsuits to protect their interests. In granting the application pursuant to 28 U.S. Code § 1782 to conduct discovery for use in foreign proceedings, the U.S. court recognized the hippos as legal persons with respect to that statute.


Hippopotamuses love water, which is why the Greeks named them “river horses.” Hippos spend up to 16 hours a day submerged in lakes and rivers to keep their massive bodies cool under the hot sun.

This U.S. statute allows anyone who is an “interested person” in a foreign litigation to request permission from a federal court to take depositions in the U.S. in support of his or her foreign case. The U.S. Supreme Court has said that someone who is a party to the foreign case “no doubt” qualifies as an “interested person” under this statute. The Animal Legal Defense Fund reasoned that since the hippos are plaintiffs in the Colombian litigation, they qualify as “interested persons.” The court’s order authorizing the hippos to exercise their legal right to obtain information in the United States is a critical turning point in the broader fight for recognizing that animals have enforceable rights.

The lawsuit in Colombia was filed on behalf of the hippos by an attorney on July 31, 2020, in an attempt to save the animals from being killed. While the lawsuit is ongoing, the regional environmental agency involved in addressing the hippo population announced it had started to provide a fraction of the animals with the contraceptive drug GonaCon on October 15, 2021. It is unknown if the Colombian government’s use of the drug will be safe and effective, and it is also uncertain how many hippos the government still intends to kill. The hippos’ lawsuit seeks an order to provide a contraceptive called PZP (porcine zona pellucida), given its historical success in hippos held in zoos and its recommendation by an international advisory committee assembled by Animal Balance, a worldwide organization that focuses on sterilization of animals.

In lieu of slaughtering the Magdalena River hippopotamuses, the testimony of two Animal Balance wildlife experts will be used to bolster support for using the PZP contraceptive to prevent the hippos from continuing to grow their population.


Hippos’ eyes and nostrils are located high on their heads, which allows them to see and breathe while mostly submerged.

What kinds of stories come out of bad situations? Ordinary hippos doing extraordinary things.

Pablo Escobar’s four original hippos most likely never knew how prolific their descendants would be, how many studies they would prompt, how they’d change our perspectives on ecosystems and the “natural world,” and how they’d advance the personhood-for-animals movement. They were just hippos, trying to live their lives.

As American broadcast journalist Daryn Kagan once said, “Bad things do happen in the world, like war, natural disasters, disease. But out of those situations always arise stories of ordinary people doing extraordinary things.”

I’d argue that, sometimes, those situations give birth to stories of ordinary hippos, too.

Here’s to finding your true places and natural habitats,