Spacer
A posthuman race native to the Spacer Guilds.They have been created by a combination of natural selection, directed-breeding programs, and germline genetic engineering. Currently, they are classified as a subspecies of Homo sapiens, but as they are still rapidly evolving, it has been speculated that they may split into multiple completely distinct posthuman species before their gene pool stabilizes, if it ever does.
External Physical Attributes
Universal Spacer Traits
All spacers are derived from pan-human stock, and this, combined with general distortions to the human form due to living in null gravity and the need to develop specific traits to better adapt to life in space, has led all spacers to be easily identifiable by a few general characteristics. Their skin and facial-features appear generally pan-huamn: dark tan skin coloration, large dark-grey to black eyes, slanted eyelids, dark hair (if they have any hair) etc. Their chests are enlarged compared to Ur Humans; in older generations, this was simply the result of organs spring-loaded against gravity bunching up in the upper torso. In later generations, where the arrangement of internal organs has been loosened to match that of an Ur Human's under gravity, the lungs have been enlarged to deal with more rareified air. Incidentally, this is one of the reasons that spacers have difficulty in even the slightest gravity- without the spring-loading on their internal organs, they tend to bunch up in the abdomen just as Ur Humans' organs tend to bunch up in the chest. Spacers are generally gracile, with thin, long limbs and expanded spines due to the lack of gravitational strain leading to low bone and muscle mass. The exception is that female spacers tend to have wider hips and higher pubic bones than Ur Human females, although the gluteal muscles are reduced. Finally, all spacers have noticeably lengthened and at least semi-prehensile toes and similarly lengthened fingers.
Variations
Size
Older generations tended to be quite tall due to spinal expansion outside the influence of gravity, but later generations have been purposefully breeding towards small size.
General Appearance
Many spacers, especially Mykenaens, have a silvery sheen to their skin tone, created by the presence of artificially engineered pigments designed to provide extra radiation protection. Many spacers have removed pubic and cephalic hair, and some have done away with all body hair entirely. Also, many spacer populations have bred for a thin layer of subcutaneous body fat for padding and insulation purposes, making all individuals look very feminine and sometimes infantile.
Body Structure
Foot structure occupies a rather large range between those who have simply lengthened their toes and reduced their heels to those who have so shortened the metatarsals while lengthening the phalanges and increasing the dexterity of their halluces that they appear almost like extra hands, which is of course their purpose. Additionally, many populations have actually taken to greatly extending the tarsal and carpal bones to effectively create double-jointed limbs. Along the lines of transforming the feet and legs into extra hands and arms, there are also large populations with greatly reduced gluteal muscles compared to Ur Humans.
Sexual Characteristics
In all cases, female external sexual organs are exactly the same as those of Ur Humans. Male sexual organs, however, range from Ur Human standard to being completely withdrawn into the body within an external covering when not in use, causing the individual to appear nearly female. As far as secondary sexual characteristics, most populations have completely eliminated pubic hair, and female breasts are generally much smaller than the Ur Human average.
Internal Physcial Attributes
Universal Spacer Traits
Low-Pressure/Null-Gravity Adaptations
In terms of internal organs, spacers are nearly identical to Ur Humans. Their lungs, however, tend to be larger and their hearts smaller and much weaker, simply due to lack of excersize rather than any particular genetic alteration. There are alterations to the cardiovascular system to prevent the lungs from outgassing oxygen in the event of pressure loss, primarily relating to alterations in hemoglobin, the airways have reflexive shut-off flaps, and spacer skin tends to be stronger than Ur Human skin, also as a protection against pressure loss. Spacer hemoglobin also has a very high oxygen affinity, and they have smaller and many more red blood cells.
Reproductive Adaptations
The most important differences between spacer and [Human|Ur Human] physiology are concerned with the female reproductive system. In the early days of spacer evolution, the infant mortality and miscarriage rates were very high due to embryonic malformations caused by the lack of gravity as well as complications in childbirth leading to a ceasarean delivery rate unparalleled in any other society. Obviously some changes must have occured in embryonic chemical signalling mechanisms via natural selection to reduce the deformation rate, but no one has yet identified exactly what these are, and so we shall focus only on the female reproductive system. Combined with low fertility rates, these problems caused population growth to barely exceed replacement for quite some time until natural selection as well as directed breeding programs expanded the bone structure of the female hip-girdle to ease delivery- this makes walking much less efficient, but of course that is a non-issue in null gravity. Successively, genetic engineering programs were introduced to reduce and control the ovulation rate. Finally, minor alterations were made to increase the fertility rate by introducing a chemical gradient within the uterus leading towards the currently active fallopian tube and altering sperm to follow this gradient rather than swimming randomly trying follow nonexistant gravitational cues.
Variations
Bone Structure
Many spacer populations have been breeding and engineering towards more bones that will grow more solidly without the need for gravitational stressing. Most of these are also pursuing programs to alter internal bone-structure to resemble that of birds, keeping their mass low.
Cardiovascular System
All spacers have expanded lungs compared to Ur Humans, but some have gone farther, increasing the density of alveoli and decreasing air-tube diameter to greatly increase surface area and oxygen use efficiency. This does, however, present some minor difficulty when they have to deal with full-density Earthlike atmospheres. To assist their smaller hearts, some populations have introduced autonomic motor programs that cause peristaltic action in the arteries. To prevent blood from rushing into the head and staying there, creating a puffed-up appearance common among Ur Humans who have not yet become accustomed to null gravity, many spacers also have expanded jugular veins to allow blood to drain more easily, although this is not really necessary.
Hibernation
Most spacers, especially those who routinely go on long-haul voyages, are altered for easier hibernation. They have engineered biochemical circuits that magnify their bodies' reactions to NOx and hydrogen sulphide, as well as a cold-temperature trigger which floods the bloodstream with massive levels of glucose, both to act as an anti-freeze and to power metabolic recovery when coming out of hibernation.
Sensory Apparatus
Vision
Many spacers are capable of seeing in the near infra-red and UV ranges. Some have eyes altered to move their lense like a mollusk rather than deforming it. Most have photosensitive pigments in their lenses that darken to filter out damaging radiation.
Touch
Many spacers are equipped with absolute temperature receptors such as are found in many birds' beaks as well as the usual Ur Human relative temperature receptors. Additionally, many have extra-sensitive body hairs used to detect air currents.
Aural Structures
Hearing is generally unmodified, although later generations often have more sensitive hearing than Ur Humans to deal with lower-air-density environments. Many populations have highly sensitive eardrums that can detect pressure variations of millibars. The semi-circular canals, which give Ur Humans their sens of balance, are fairly useless for their original purpose, but have been modified in many populations to create highly sensitive accelerometers.
