The eyes of a fish-eater polarize light, removing the bright reflections that normally prevent land animals seeing below the surface of water. Its brain automatically compensates for the refraction.
The fish-eater, Piscator longidigitus, is an upland-dwelling, semiaquatic, piscivorous descendant of the temperate woodland-dweller, from 3 million years (the 30020th Century), from Man After Man: An Anthropology of the Future. It is a patient hunter, waiting for freshwater bony fish to swim closer in range.
Three million years have passed and the results of constant natural selection and evolution are apparent. The temperate woodland-dwellers have diversified, and developed specialized body forms to fit different environments.
Living by upland lakes and beside rivers, the fish-eater is equally at home on land and in the water. Its pelt is smooth and glossy, its shape streamlined. Ears are small and close to the head, the neck is short and feet are broader than usual.
The brook burbles down the slope, bouncing off the exposed rocks and rubble in the gully, washing soil from the banks beneath the hanging tangled roots of the great deciduous trees. Newly-hatched flies weave and gyrate in the cool sunlight above the little pools and backwaters that gather beneath and behind the waterfalls. The exposed rocks are pocked by smooth circular potholes, worn by the swirling stones caught up in the infrequent floods. At present, though, the stream is flowing with gentle splashes and gurgles, through the V-shaped cleft in the soil, and downwards through the wooded hillside towards the distant plains.
The air is cool, almost as cool as it was during the ice ages of ancient times. There can be no more now for a very long while. The continent at the South Pole is covered with ice, but there is no permanent icecap in the north. The gradual movements of the continents has opened the oceans to such an extent that warm currents from the Equator now sweep up to the polar sea and keep it permanently free of ice.
There is less carbon dioxide in the atmosphere than there has been for a long time, and this is the reason for the cooling. Sunlight shining down onto Earth's surface is reradiated away into space, with little of it being trapped in the layers of air. The algae that were induced to grow on the lowlands by the aquatics have absorbed much of the atmospheric carbon dioxide, and now it lies trapped in vast deposits of peat and lignite below the roots of the forests of the coastal plains. The aquatics themselves have long ago abandoned that wasteful exercise, and now grow more concentrated food out at sea.
In the shadow beneath an overhang, screened by the interwoven arches formed from the sturdy roots of a great tree and by the more delicate soil-clogged roots of the grasses and undergrowth plants, there sits a figure. If he had the wit to interpret them, the rocks in the bank behind him would tell him of an important part of his history. They are normal strata of dark finely-bedded shale, except for one thin layer which is quite unusual. Shale is formed from compacted mud that was once deposited layer upon layer in quiet waters, but this one particular bed of the sequence seems to consist of a different material altogether. It looks as if all kinds of foreign matter spread in and were deposited on top of the mud at one particular time. It is a very thin bed, and so the deposition could only have taken place in a period of a few thousand years at the most. The top boundary of this layer is as abrupt as the bottom, and above this the normal sequence of shale continues, showing the continuing deposition of clean mud. Evidently the continuous deposition of mud in the area had been disrupted for a short period while great changes took place in the world at that time, and the resulting bed of foreign matter had eventually been turned to rock along with the mud above and below.
The figure has never noticed this. It is not part of his life and he is looking the other way. Sunlight, sparkling from the pool below him, casts ripples of light on his face and arms. He has the long limbs and the long face of one of the hunting people, but there is something a little different about him. His neck is shorter, his ears smaller, his fingers longer, and his feet broader than usual. Also, his eyes are strange (not in their appearance but in their function). The lenses smooth out the bright reflections from the water's surface enabling him to see directly into the depths. His brain compensates for the refraction and distortion caused by the different densities of the water and the air. He uses these faculties to watch the bottom of the pool for his prey, for this creature feeds on fish.
In the temperate regions of the world, where the forests and woodlands still exist on the upland slopes, the hunting people still pursue their age-old lifestyle, just as they have done since they were engineered. However, as there are so many different food sources in the habitat, many of them have begun to specialize, and to develop bodily forms that are appropriate to their particular way of life. Most lie in wait for birds, or dig in the ground after burrowing mammals. Some even feed on nothing but insects that they remove from the layers of their wooden homes.
One group has developed as an almost exclusive fish-eater. Living mostly by the hilly lakes and rivers, these creatures spend most of their t
The fish-eaters have evolved by natural selection the streamlined shape earlier engineered into the aquatics.
ime on dry land, but enter the water to chase their prey. Their broad feet help them to swim, and their long fingers can spear their slippery prey with ease. Their pelt has become particularly smooth and glossy, and they are beginning to adopt a streamlined shape to their bodies, with a bulbous head tapering into the smooth shoulders without much of a neck. Their eyes work best above the water, but their focus can be adjusted to allow their use beneath the surface as well.
The individual beneath the overhang (so still that he appears to be asleep) suddenly focuses his eyes on a movement not far below the surface of the pool. A long fish swims in from the more turbulent area near the current, its deep tail whisking back and forth, moving its body lazily along with an ease that would make the watcher feel jealous if he had the capacity to feel such emotions. Taking his time, he watches the creature come closer and closer.
His hand cleaves the water so expertly that it hardly makes a splash. The pointed claws on the long fingers close around the scaly body, and pin it before the slippery shape can wriggle free. Then, with an almost reflex jerk, he yanks it from the water and onto the bank beneath the overhang.
With a swift blow he kills it.
Then he eases himself from his hiding place, straightening out the slight cramp in his muscles, and gathers up his catch to take it back to his mate and family.
No, he is not a fully-adapted water creature. There are other derived humans in the world who are more perfectly built for the water environment. Nevertheless he is good enough to survive and to continue his line.
By 5 million years (the 50020th Century)[]
They are wiped out by the Travelers of the stars.