There was a time when doctors performed surgery on infants without anesthesia. And I don't mean centuries ago. This happened in the 1980s, and it wasn't rare. Somehow, despite babies crying or screaming, the medical community had convinced itself they couldn't feel pain.

A lot of the reasoning had to do with the belief that infant brain pathways were too immature to register the sensation. And a massive contributor to the horrifying misunderstanding was that the tiny patients couldn't verbalize their emotions. They couldn't say: "I'm in a lot of pain. Please help."

Then in 1987, the American Academy of Pediatrics finally deemed the practice we'd now consider barbaric to be unethical. Study after study showed that infants do feel pain like us. And I know I'm not alone in my shock that this practice wasn't remedied sooner. 

But what if humanity is unknowingly falling into a similar trap all over again? What about the emotions of animals?

Like infants, animals can't say: "I'm in a lot of pain. Please help." And many can't even cry, yet there's a growing abundance of research to suggest that animals across the spectrum -- from octopuses to fish to bees -- experience emotional and physical pain, and sometimes even anxiety.

In 2011, for instance, researchers conducted a study on honeybees that involved agitating them by shaking them around. After analyzing the bees, the team saw they exhibited brain chemistry changes, like lowered serotonin, that are directly associated with anxiety, depression and other negative psychological states.

"For animals, we've gone through the same sort of stages, in the sense that, since animals don't talk, their feelings were denied," Frans B. M. de Waal tells me. He's a biologist, primatologist and professor emeritus at Emory University, who's also the author of best-selling books like Are We Smart Enough to Know How Smart Animals Are? "It's very strange that people have denied pain in fish for so long, and that's because fish don't call out when they are in pain."

In a new review, published Thursday in the journal Science, de Waal lays out what we know so far about animal emotions -- and what this knowledge might ask us to change in our moral framework as the humans who live among them, test them for science and even eat them.

"Although we are used to thinking about how our actions affect other humans, recognizing widespread animal sentience requires us to also notice -- and consider -- our impact on other species," de Waal and fellow author Kristin Andrews, a professor of philosophy at York University and York Research Chair in Animal Minds, write in their paper. "This way, animal sentience is bound to complicate an already complex moral world."

On the bright side of things, the treatment of animals has steadily been improving over the years, especially of mammals that can cry out in pain or somehow indicate they feel negative sensations, the review notes. 

Dogs, dolphins and cows can yell when they're being hurt, making it much easier for us to empathize with them. And researchers have very strict rules in place for scientific studies that employ animal subjects. When I worked in a laboratory testing mice, I attended a week of specialized training to learn just how to ethically handle and euthanize them. We had a protocol, and if I didn't follow it, there'd be consequences.

But when it comes to species that appear insensitive to painful sensations, like fish, or those that might require complex mechanisms for more-than-baseline comfort, like farm animals, we might have work to do. 

"We can do a lot better," de Waal says. "I've worked all my life with primates in captivity, and it's a rule that primates need to be kept socially ... they have to be kept in a small group. And I think for primates, that's a good rule. But I also know that, in practice, many labs still keep monkeys in single cages."

De Waal also calls out the total lack of laws surrounding ethical treatment for invertebrates.

"We have all sorts of rules for rats and mice -- how you need to treat them, and how you need to kill them, and so on," de Waal says. But despite indications that invertebrates experience sensation too, "we don't have that for them."

Lobsters are invertebrates, and chefs boil these animals alive. This situation might be different if lobsters could look us in the eye and say something like, "I'm in pain."

"In the history of research on emotions, feelings have usually been denied to anyone who cannot speak," de Waal says. "And that's a very strange position because, of course, feelings don't require language. It's not as if you cannot feel if you don't know the language."

Even though we may not know exactly what animal emotions are -- because they can't communicate them through language -- the review says we can identify when they experience negative emotions or positive emotions. 

Some researchers have suggested that organisms that are simpler than humans could have less-developed emotions, and other researchers, de Waal explains, believe the opposite. Perhaps simpler brain chemistry, and thus the inability to contextualize emotions, makes their sensations worse or unceasing. It might be best to use a blanket rule when considering how to ethically treat animals, rather than discriminate by which animal feels the "most" emotion. 

We just don't know yet. Though what we do know is that those emotions exist.

Knowing that animals feel emotions gives rise to a glaring question: Is it unethical to eat them? One extreme might be to say we shouldn't do anything to harm animals at all, ever. No eating, testing or anything else. The other might be to say that what you do to animals doesn't matter.

"I think we need to end up somewhere in between," de Waal says. "You need to take the sentience of animals into account. You cannot just act as if they are rocks -- that's a bit of what we're doing at the moment, in the agricultural industry."

Every day, crowds of chickens, cows, pigs and sheep are tended to on farms "in cooped-up spaces," de Waal says, "without sunlight and without air." De Waal says that when considering a shift in our moral actions, we need to focus on these farm animals, and not just on animals in research labs, with strict regulations, or zoos, with trained professionals. Farm animals, de Waal says, would probably consider a zoo to be a "paradise."

In the end, thinking about how to navigate animal emotions might bring up more moral questions than are answered. Regardless, de Waal says, something needs to change, especially with regard to farm animals. And it's our responsibility to figure it out.

"We're basically treating them as if you can do anything you want," de Waal says. "I don't think that's the right attitude."

Correction, March 26: The original version of this story misstated Kristin Andrews' background. She's a professor of philosophy at York University and York Research Chair in Animal Minds.