Humans have bred fruits to be so sweet, a zoo had to stop feeding them to some animals

Thinking about how human activity has changed his favorite foods.
Thinking about how human activity has changed his favorite foods.
Image: Reuters/Rebecca Naden
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On Sunday, the Sydney Morning Herald reported that zookeepers at the Melbourne Zoo are weening some animals off of fruits because they were too sweet for the animals’ own good. Red pandas and primates had been gaining weight, and some had signs of tooth decay as well.

“The issue is the cultivated fruits have been genetically modified to be much higher in sugar content than their natural, ancestral fruits,” Michael Lynch, the zoo’s head veterinarian, told the Sydney Morning Herald.

For the most part, Lynch is referring to the selective breeding of plants that humans have been doing for some 9,000 years, since the dawn of agriculture. Though we don’t typically think of traditional crop breeding as a form of genetic modification, it is. Today, advances in genetic sequencing have allowed farmers to genetically engineer certain crops, which essentially speeds up the breeding process. It’s often used to make versions of a crop that is virus- or pest-resistant.

Genetic modification of either kind—traditional or high-tech—isn’t inherently dangerous or safe; that depends on the results. The processes have given rise to a lot of foods we love: Bananas with tiny seeds, watermelon full of thick, red interiors, peaches the size of our fists, and corn on a nice, thick cob. Today we get more of the flavor and nutrients from a single fruit than we ever have before.

That means more sugar in fruits, but that sugar is good for us. As Annaliese Griffin has previously written for Quartz, the fructose in raw fruits is packaged in fiber, which means it’s harder for our bodies to break down. As a result, it can’t spike the levels of sugar in our blood the way refined sugars, like those added to candy or a soda, do.

Some animals at the Melbourne zoo, particularly red pandas and monkeys, have developed a sweet tooth for the genetically modified fruit they’ve been given over the years. If they could, many of them would eat mostly fruit and completely ignore other, less sweet foods that are normally provided to them to try to help them maintain a balanced diet, Lynch told the Herald. In captivity, zookeepers had previously been feeding red pandas and monkeys diets high in fruit, to mimic what they’d eat in the wild. However, wild fruits are a lot less sugar-dense than what we’ve made for ourselves.

The solution for zoo animals is simple: Keepers have switched red pandas diets from fruits to little nutritional pellets sweetened with just a bit of pear, and trading out fruits for other animals with green, leafy vegetables, which are still rich in nutrients.