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You won’t believe what humans, birds, and reptiles have in common

Published Aug 13th, 2020 11:20PM EDT
science news
Image: tugolukof/Adobe

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  • Researchers studying the makeup of tears from various species have discovered that humans, reptiles, and birds have similar tears. 
  • The research could lead to new treatments for veterinary use.
  • The levels of certain electrolytes in tears are very similar across our various species.

Humans are unique creatures in many ways. We have highly advanced cognitive abilities and our brains have allowed us to perform stunning feats (and plenty of terrible things, too). Still, we’re just animals, and that means we share things with other animals that are sometimes shocking.

In a new study published in Frontiers in Veterinary Science, researchers reveal that birds and reptiles are incredibly similar to humans in one surprising way: our tears. As the scientists explain, the makeup of human tears closely mimics that of species of reptiles including crocodilians and birds like parrots.

As CNN reports, the research was conducted in Brazil, with scientists collecting tear samples from a variety of different animal species including hawks, parrots, tortoises, sea turtles, and caimans. When compared to human tears, they weren’t an exact match, but they were much closer than you might expect, with similar levels of certain electrolytes.

“Although birds and reptiles have different structures that are responsible for tear production, some components of this fluid (electrolytes) are present at similar concentrations as what is found in humans,” Arianne Oriá, lead author of the study, said in a statement. “But the crystal structures are organized in different ways so that they guarantee the eyes´ health and an equilibrium with the various environments.”

Distinct changes in the crystalline structures of the dried tears of aquatic animals like sea turtles and caimans suggest their tears are specialized for their environment. The researchers suggest that adaptations in tears may not always have natural triggers, and that pollution may also play a large role.

“Tears are the most exposed fluids to the environment. So, with subtle modifications to the environment, the tears will modify. For example, in humans, we know that people who smoke have their tears modified,” Oriá said. “If we modify our habitat with pollution or something else, we will create an unhealthy habitat for our tear film. So animals, as well as humans, will have to have many many years to re-adapt to the habitat.”

Understanding the tears of other species could lead to advancements in both veterinary medicines or even offer scientists hints as to how to make human eye treatments more effective. Ultimately, however, the research will likely benefit animals the most, especially ones that are found sick.

“It’s important to understand healthy animals in order to treat sick animals, because species depend on their vision,” Oriá says. “Animals are not able to live without vision in the wild. A sea turtle without vision will die.”