Rodents make up 75 percent of all animals used in scientific testing. They breed easily, and their physiology and genes overlap enough with ours to stand in for us.Take them away and the vaccines still need testing. The drugs still need trials. The question is simply who does the testing on.In a world without wildlife, the answer starts pointing uncomfortably back at us.Avoiding dangerous encounters on a wilderness walk sounds appealing until you consider what wildlife actually does. Animals keep Earth’s biodiversity in balance, and without them the repercussions land squarely on our species.There have been five major extinctions in Earth’s history, and we may be entering a sixth. Events on that scale wipeout 75 to 90 percent of all species, and they can be traced geologically through the chemical composition of rocks and fossils.For the last 11,500 years we have been living in the Holocene Epoch, which began as the last Ice Age ended. Many scientists argue we have already moved into something else, the Anthropocene, starting either with fossil fuels and the Industrial Revolution or, some suggest, as far back as the invention of farming.Either way the pressure keeps building. As our population grows, so does demand for food, fuel, and plastic production, while wildlife populations shrink.A recent intergovernmental report estimates that up to one million animal and plant species are on the brink of extinction.Which brings us to medicine, and the part most people never consider. Over 50 percent of modern medicines and 90 percent of traditional medicines derive from wild plants and animals.Lose the animal trials and researchers would have to fall back on computer modelling and in vitro tissue culture design. That transition would not happen overnight, and it would be an expensive logistical nightmare for scientists everywhere.Meanwhile the ingredients themselves would vanish too. Viper venom is used in blood pressure medication. Insulin has come from the pancreases of pigs. Those are not luxuries.Food is the next problem. Milk, cheese, hamburgers, all of it becomes a memory, and we would have to scale lab grown meat and vegetable production dramatically just to keep people fed.Then there is the part happening invisibly in the ocean. Plankton generate a huge portion of the planet’s oxygen and help regulate the climate. Without them, breathing itself gets harder.Bees and other pollinators are the same story on land, keeping vital plant life growing. Replacing them would mean inventing new technology to pollinate artificially, whether through insect drones or engineered wind systems.Even your wardrobe changes. Without silkworms, sheep, and properly pollinated cotton crops, silk, wool, and cotton all become scarce and expensive, leaving synthetic fabrics as the default.And the companionship disappears with everything else. Robotic pets exist, and they are simply not the same thing.There is genuine good news, though. Conservation work is producing results.Whale populations are approaching their pre whaling numbers. The bald eagle, once close to extinction, is recovering. And the gorillas of Virunga National Park continue to thrive because people committed themselves to protecting them.Plenty of work remains. But that work is the difference between a world that keeps its wildlife and one where the only available test subjects are the ones reading this.