“I’ll believe it when I see it.”
Try telling that to your dog or a fly. See what exactly? That hummingbird visiting flowers sees things quite differently than you or I, even if between individual humans our vision can be quite varied. Understandably, we tend to get a bit caught up in ourselves, because despite good science we still only really know definitively what the world looks like to us (and by that I mean down to each of us individually).
What does the world look like to some of the animals that we share the Hill with?
First, a bit about “eyes.”
Any eye, no matter the structure, detects light and processes it into neurons that help the organism with said eyes “see.” Enough said. But without getting too metaphysical about it, what exactly is seeing? For some organisms, it means merely detecting light and dark. For others it means seeing colors, shapes, and movement. There are simple eyes which consist of a lens or multiple lenses within a single structure (like our eyes or an eagle’s) and compound eyes are arrays of many lenses (think of fly eyes). The arrangement of these lenses and the photoreceptor cells are quite diverse and complex (even in the case of “simple” eyes) and although Darwin famously said that “the eye to this day gives me a cold shudder,” it’s fairly apparent why this is the case: organisms have deeply different needs from their eyes.
To attempt to briefly explain the evolutionary development of eyes, or even try to explain all the details of the different eye structures of even the few creatures below is laughable. So I’ll settle down into my childhood comfort zone and regurgitate some animal facts. I do this for your sake, because while eye evo-devo is a vast and fascinating subject, the real joy is knowing that slugs have no focus, and that birds can see an entire spectrum of light invisible to us.
Cats — Cats are obviously good at seeing at night. If you’ve ever caught your cat’s eyes in a flashlight, you also know their eyes are not like ours. Cats have a reflective layer called the tapetum lucidum, allowing them to see with much less light than us (around 1/6th the amount we’d need to see well). This is also why they have irises that can go from narrow slits to wide moons; they are extremely sensitive and need to protect themselves as they move between day and night. Continue reading