In previous research, other scientists had used embryonic stem cells to grow optic cups, the structures that develop into almost the entire globe of the eye during embryonic development. And other research had developed optic cup-like structures from induced pluripotent stem cells.
Rather than grow these structures directly, Gopalakrishnan's team wanted to see if they could be grown as an integrated part of brain organoids. This would add the benefit of seeing how the two types of tissue can grow together, rather than just growing optic structures in isolation.
However, if you want to argue the natural evolution of the eye, it's super easy. Convergent evolution says much, the eye has clearly evolved multiple times.
Start with a patch of light sensitive cells, may helps you hide when predators swim overhead. Iterate from there. Now you got humans with medium range vision, raptors that can spot a mouse from 100' up, octopi with radial optic nerves that have no blind spot. And that one's pretty funny. If god designed our eyes, why did he put the optic nerve in the back, making us partially blind and having to use processing power to fool us into not noticing?
