Humans are fairly fragile organisms. Sure we live just fine on the surface of the Earth, as long as there is enough air and the temperature is neither too hot nor too cold. That means that we cannot explore the more extreme areas of our planet - or any planet - without technical assistance of some kind. Currently it's good old-fashioned engineering that allows us to delve the ocean depths or journey into space.
The science fictional approach is a bit different: instead of building machines to protect fragile human bodies, bioengineer human bodies to live in more extreme environments. While many of them might appear to be the mermaids of sailor lore, most are much stranger. Here are a few of my favorite examples:
James Blish's Microscopic Water Humans
"Webbed extremities, of course, with thumbs and big toes heavy and thornlike for defense until the creature has had a chance ot learn. Book-lungs, like the arachnids, working out of intercostal spiracles - they are gradually adaptable to atmosphere-breathing, if it ever decides to come out of the water. Also I'd suggest sporulation. As an aquatic animal, our colonist is gong to have an indefinite lifespan, but we'll have to give it a breeding cycle of about six weeks to keep its numbers up during the learning period; so there'll have to be a definite break of some duration in its active year. Otherwise it'll hit the population problem before it's learned enough to cope with it." ~ "Surface Tension"
In James Blish's 1952 classic short story "Surface Tension" humans crash land on a water covered planet. As their supplies are running out they create a race of microscopic aquatic humanoids to carry on their legacy. The small creatures eventually develop technology advanced enough to escape the bounds of their environment, breaking through the surface tension of their watery world in an "air ship".
Orca felt tired after the long swim from Harmony to the spaceport. She swam into the ferry dock, pausing where water and air and the metal ramp intersected. The air world began to come back to her. Her metabolism slowed and she felt chilly. She never noticed the cold, deep in the sea. [. . .] The afternoon breeze slapped small waves against the sides of the port and dried the droplets of water clinging to the fine hair on Orcas arms and legs. She stretched, spreading her webbed hands to the sun. ~ Superluminal
Divers - humans genetically engineered humans to live under water - appear in a number of Vonda McIntyre's stories. Their characteristics are more practical than beautiful: they have gills, insulating fur, webbed toes and fingers, the ability to hear and produce the same sounds as whales, and, for the men, dolphin-like retractable penises. Even with all those modifications, they can still breath regular air, live on land, and travel to the stars.
Vargovic had seen pictures of mermaids in books when he was a child; what he was looking at now were macabre corruptions of those innocent illustrations. These things were the same fusions of human and fish as in those pictures - but every detail had been twisted toward ugliness, and the true horror of it was that the fusion was total; it was not simply that a human torso had been grafted to a fish's tail, but that the splice had been made - it was obvious - at the genetic level, so that in every aspect of the creature there was something simultaneously and grotesquely piscine. The face was the worst; bisected by a lipless down-curved slit of a mouth, almost sharklike. There was no nose, not even a pair of nostrils; just an acreage of flat, sallow fish-flesh. The eyes were forward facing; all expression compacted into their dark depth. ~ "A Spy in Europa"
In Alastair Reynold's stories set in the Revelation Space universe, extensively bioengineered humans spread throughout the solar system. Among them are the Denizens and Gillies. Most Gillies have relatively minor modifications that allow them to live and work under water, such as gills on their chests. Denizens, on the other hand, were engineered as slave labor for the oceans of Europa. They have fewer human characteristics than the Gillies, and are able to breathe hydrogen sulfide instead of oxygen and have great physical strength. Originally they were only able to survive near thermal vents, but introduction of genes for the "antifreeze" proteins found in Antarctic fish allow the Denizens to survive anywhere in Europa's oceans.
"Representatives Freedom come," Jason pulsed. The mer, unlike dolphins or other marine mammals, used gills and had no air available to create sonar. Instead they had a small bone, equivalent in basic design to those of the inner ear, located in the nasal passages in their forehead. They could send commands to the bone that pulsed their words and turned them into high frequency sonar. It was also adequate, barely, to maneuvering in zero visibility, be that in the dark or in a cave or even in light silt. And they could receive and process, to an extent, the sonar images created by the delphinoids, who had a much more advanced system. But for conversation, the mer relied on verbal shorthand. ~ Emerald Sea
In John Ringo's Council Wars novels, Earth has become peaceful under the control of a computer called Mother. Genetic engineering has populated future Earth with elves and dragons and mer-folk, as well as Changed humans in the form of orcas and dolphins and manta rays and other beasts. While science fictional, the stories also include characters who are sword-wielding "reenactors" and near magical technology, which give the novels the feel of epic fantasy.
"I thought the Sharers engineered themselves to fit the planet, not the other way round."
"They did, of course: their webbed digits, their epidermal symbiosis with breathmicrobes. But that's only half the story. Today, none of Shora's species produce amino acids toxic to produce amino acids toxic to humans. In fact, many synthesize the precise ratio of amino acids needed for human nutrition. By contrast, on all other unterraformed worlds, the native flora and fauna are inedible. [...] It's not clear what happened, but around ten thousand years ago, the time Sharers got started, the fossil record shows widespread extinction." ~ Daughter of Elysium
Joan Slonczewski introduces the Sharers in her novel A Door Into Ocean. The Sharers are an all-female society of genetically modified humans living on the ocean planet Shora. While the Sharers live on giant floating "raft trees" rather than under water, their skin contains purple breathmicrobes which allow them to spend an hour under water, they have translucent eyelids that protect their eyes like goggles while diving, and webbed hands and feet. From their rafts they manage the planet's ecosystem with their advanced biomanipulation skills.
Unfortunately, Slonczewski's stories involving the Sharers are available for free. I recommend seeing if your library carries her novels.
Here are few more free short SF stories with humans engineered for ocean working and living:
Image Credit:Atomic Bear Press Peggy Kolm is the creator of Biology in Science Fiction, a blog that covers the marine world as well as other biology-related topics in science fiction, including engineering, cloning, and aliens. Peggy has kindly offered to write a series for The Reef Tank of special marine-related blog entries related to science fiction for The Reef Tank.