The virtual assistant in iOS can do all kinds of stuff, of course. But here are the 16 things we think everyone should try at least once.
In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision.
The earliest predecessors of the eye were photoreceptor proteins that sense light, found even in unicellular organisms, called eyespots. Eyespots can only sense ambient brightness: they can distinguish light from dark, sufficient for photoperiodism and daily synchronization of circadian rhythms.