At Penrhyn Glas, a dozen shapes were bobbing in the green water of Porth y Gwichiaid, the \u201cwinkle cove\u201d. We peered at them. The shapes seemed to peer back. Given the spread of visual acuity in our small group, there was some confusion about what we were seeing. It wouldn\u2019t be the first time one of us had mistaken a fisherman\u2019s buoy for a creature\u2019s head. For myself, while everything at the end of my nose is a blur, objects at a distance have uncanny clarity. The distinguished profile, the colouring, the shape of the nostrils could only be a grey seal.<\/p>\n
We edged closer to the shoreline and as we did so, the seals lifted themselves further out of the water, also fascinated. Every so often, one would turn and slip under the water and then re-emerge at a slight\u00a0distance to resume viewing. I knew what I\u00a0could see, but what about the seals?\u00a0Their ancestors were mustelids, like otters or weasels, which, as Darwin theorised, made the natural transition from freshwater to salt. As it spent more time at sea, the proto-seal\u2019s eye evolved to new conditions. Otters have some perception of colour, having two cone receptors in their eyes, but seals lost one along the way. They can differentiate colours\u00a0from subtle contrasts in brightness, but otherwise their world is monochrome.<\/p>\n
The payoff was an enhanced ability to see in the low light of the ocean depths. Seals routinely dive to 50 metres, but can go much deeper than that. Yet they breed onshore and spend their first weeks out of the water. To manage these extremes, the seal has a powerful iris that can squeeze its pupil to a pinhole in the strong light of a late summer sky. Some paleoanthropologists have speculated that we also evolved along the sea\u2019s edge, prospering from its rich food supply. Aspects of\u00a0our physiology offer some evidence for this. The seal went the other way, from land to ocean. Standing or floating, we watch each\u00a0other, wondering.<\/p>\n