Humans evolved from 4-eyed weirdos: Meet the great-grandfish that had extra eyes to escape predators

Fossils have a way of rewriting family trees, pulling back the curtain on creatures that feel alien and oddly familiar, like distant cousins we never knew we had.

Half a billion years ago, oceans were full of experimental life forms during the Cambrian explosion, when evolution was throwing everything at the wall to see what stuck. These weren't just random blobs; they were the roots of spines, brains, and eyes that let tiny swimmers spot danger in murky waters.

Earth was dotted with four-eyed ancestors

Rare fossils from China's Chengjiang beds, dating back 518 million years to the Cambrian period, show our earliest vertebrate relatives as a jawless fish called myllokunmingids, and they had four eyes. Two larger ones flanked the head's sides, with two smaller ones centered up top, all image-forming like camera lenses.

"This changes how we think about the early evolution of vertebrates. It turns out our ancestors were visually sophisticated animals navigating a dangerous world," said study co-author Jakob Vinther, associate professor at the University of Bristol, in a statement, according to a news report.

Species like Haikouichthys ercaicunensis and an unnamed myllokunmingid had these kinds of features and are preserved in detail, despite soft eyes rarely fossilising.

Why four eyes?ns

Back then, oceans turned deadly as big predators emerged, pressuring small, soft-bodied swimmers. "In that environment, having four eyes may have given these animals a wider field of view, important to avoid predators," Vinther explained. Noodle-thin and vulnerable, these ancestors used extra peepers for panoramic vision amid the chaos.

What did scientists observe during analysis?

Lead author Peiyun Cong of Yunnan University and the team used microscopes and chemical tests to spot melanosomes, light-absorbing pigments, and lenses in all four eyes. "We started by examining the obvious large eyes to understand their anatomy - and it was a complete surprise to find two smaller, fully functional eyes between them. Seeing that was incredibly exciting," Cong shared.

The smaller central eyes connect to a "third eye" feature seen in some modern vertebrates, like the light-sensing parietal eye in lizards, and to the pineal gland deep in our brains, which produces melatonin to help regulate sleep.

"What we're seeing is that the pineal organs began as image-forming eyes. Only later in evolution did they shrink, lose visual power, and take on their modern role in regulating sleep," Cong noted.

What does this tell us about evolution?

This changes ideas of simple early eyes, suggesting four-eyed vision was ancestral, later simplifying to two as seas calmed. Published in Nature, the study traces our lineage from these survivors.