The thorny ethics of hybrid animals

One of the greatest movies of all time, Napoleon Dynamite, introduced many to the scientific concept of hybridization:

Ligers, the hybrid offspring of lions and tigers, are real, though their “skills in magic” are still under investigation by top scientists.

The creatures are likely only man-made creatures, since the habitats of these two big cats only overlaps in India’s Gir Forest. Their mashup names belie their origin stories, with an offspring taking the first half of its name from its father and the second half from its mother. Endless fun can be had with this naming convention:

Lion father + tiger mother = liger.

Tiger father + lion mother = tigon.

Leopard father + jaguar mother = jagleop.

Lion father + jagleop mother = lijagleop.

Real ligers often suffer from genetic defects, like excessive growth. Credit: Wikimedia.
Real ligers often suffer from genetic defects, like excessive growth. Credit: Wikimedia.

The fun sort of drains out of this exercise, however, when you learn of the health issues associated with these hybrids. Ligers, for example, grow big… too big for their own organs, in fact.

Many big cat hybrids suffer birth defects and never make it to adulthood. If they do, they can pass these mutations on to future generations because, though the males are sterile, the females are fertile.

Many species can crossbreed, not just big cats. There’s zonkeys (zebras + donkeys), camas (camel + llama), pizzlies (polar bears + grizzlies), and many, many more.

These animals fetch a premium on the exotic animal black market, often to disastrous consequences: at least 19 people have been killed and 85 hurt in the U.S. by privately kept wolf-dog hybrids since 1982.

Due to all these factors, hybridization in captivity is understandably widely opposed by conservationists. But, hybridization can happen naturally, and that is a much muddier issue.

Yoamel Milián-García. Credit: ResearchGate.
Yoamel Milián-García. Credit: ResearchGate.

“Natural hybridization it is not bad at all. It’s part of the evolutionary process,” said Yoamel Milián-García, biologist with the University of Havana on the island of Cuba.

Miles and members of MOBProd met Milián-García in July when they visited Cuba. Milián-García is working to determine the genetic makeup of the Cuban crocodile population. In a seminal 2015 paper, he found that almost half of the wild Cuban crocs in his sample of 227 were hybrids with the American crocodile. To compare, only 16.1 percent of a group of 137 Cuban crocs raised in captivity showed genetic indications of hybridization.

As Miles reported for the PBS NewsHour, the Cuban crocodile is highly endangered–with only around 3,000 individuals left roaming in the wild. Much of the issue has been the intense poaching of these animals for their skin and meat, especially during Cuba’s food shortage in the 1990s.

The American crocodile, despite its name, is also native to Cuba and is doing quite well. They are more shy and harder to catch than their Cuban comrades, so they are less at risk for poaching. The fact that there is more hybridization in the wild than in captivity points to a natural evolutionary response to an environmental pressure, albeit one imposed by humans.

“We are trying to understand if this is part of the natural process,” said Milián-García. “If that is part of the natural process, it doesn’t mean that we are necessarily going to lose the Cuban crocodiles.”

Organisms naturally hybridize in the wild, making it difficult for scientists and conservationists to disentangle which ones are human-caused and, hence, should be controlled. This natural hybridization is likely extremely important for the creation of new species: about half of all plant species on Earth arose due to hybridization. Even humans participated in this hybridization early in our history–many of us carry a few percent of Neanderthal DNA.

Natalia Rossi.
Natalia Rossi.

“The debate goes deeper because Yoamel found that American crocodiles from Cuba are more closely related to Cuban crocodiles of Cuba than with American crocodiles of the continent,” said Natalia Rossi, a colleague of Milián-García who works for the World Conservation Society.

So, these hybrid crocodiles are fairly close to being fully Cuban. Deciding when to intervene is tricky for conservationists. Sometimes, hybridization is the sole path for saving the remnants of a species, like the efforts that kept the Florida panther population from extinction by crossbreeding them with Texas cougars.

“There are many species that hybridize in the world,” said Rossi. “In the case of Cuban crocodiles, so far, the decision is just to do nothing in terms of eradicating hybrids.”

Miles pets a wild Cuban crocodile that was just caught in the Zapata swamp.
Miles pets a wild Cuban crocodile that was just caught in the Zapata swamp.

How new species form–and what even defines a species–are difficult questions for scientists. Science can answer some of these questions, but is mute on the moral questions such as intervention. These are issues that need to be addressed by conservationists, ethicists, even philosophers.

While the moral implications are being sorted out, there are still 3,000 Cuban crocodiles–and many other species around the world–that need protection.

“In our lifetime, we can study the past. We can try to have some predictions about the future. But what we can really do is to protect what we have,” said Rossi.


A version of this story appeared on the PBS NewsHour website.

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