Finally, whether a chimerical donkey-horse was interfertile with either donkeys or horses would depend on which cell line comprised its reproductive system. Even if the rest of its outward appearance were that of a donkey, if it had 100% horse cells in its reproductive system, when bred to a horse, it would produce a 100% fertile horse, with a full 32 pairs of horse chromosomes, and no donkey characteristics whatsoever.
Understanding this distinction is crucial for understanding Swenson’s Ape reproductive physiology and secondary sexual characteristics, because Swenson subsequently found that all Swenson’s Ape species are profoundly chimerical. Chimerism not only occurs within and across all Swenson’s Ape species; it is both a usual and an essential part of their reproductive lifecycle.
Most Swenson’s Ape matings result in multiple zygotes (fertilized cells), that is, fraternal twinning. Thereafter, any or all of four types of chimerism may (and usually do) occur. These are: stem cell transfer, tetragametic, germ line, and parasitic chimerism. This means that Swenson’s Ape offspring may inherit multiple cell lines from each parent, and these cell lines may or may not be fused n vivo. In the upper classes, parasitic chimerism results in asymmetry, as discussed below.
Stem cell transfer occurs via cross-placental blood-vessel connections between twins, and is especially common for stem blood cells. In this case, the individual’s bloodstream, immune system, and bone marrow will have different DNA from other parts of its body.
Tetragametic chimerism occurs through the fertilization of exactly two ova (two gametes) by exactly two sperm (two more gametes), followed by the fusion of the zygotes (the two fertilized eggs) at a very early stage of development. This results in an individual with intermingled cell lines. That is, the chimera is formed from the merger of two fraternal twins. The resulting individual can be male, female, or both. In Swenson’s Apes, for reasons as yet not well understood, both is most common.
Similarly, germ line chimerism occurs when multiple ovi are each fertilized by one or more sperm. The fertilized eggs then divide, and the resulting blastocysts (cell clumps) may or may not fuse to form one or more chimeric embryos. These embryos exist for a fairly extended period prior to implantation, and then may attempt to implant at the same hemophore (blood vessel node.). In this case, the embryos merge. If this happens, one embryo atrophies, except for the reproductive cell lines, which complement those of the other embryo. The twin then develops normally, except that it bears the reproductive cell lines of its sibling. If the merged embryos were of opposite sex, this results in a truly hermaphroditic individual. Again, in Swenson’s Apes, for reasons as yet not well understood, this is the most common outcome.
Parasitic chimerism occurs slightly later in embryonic development, when a “male” embryo attaches to a “female,” eventually fusing into a single, hermaphroditic individual with a shared circulatory system. “Male” and “female” are indicated parenthetically, because at this stage of development, the embryo consists of little more than an undifferentiated alimentary canal, with no developed digestive capacity or limb differentiation, and either or both embryos may already be stem cell, tetragenetic, or germ line chimeras.
The War Between the Sexes
In a further elaboration of this trend, all asymmetric Swenson’s Apes (that is, classes excluding Swenson’s Marmosets and Swenson’s Shrews) are chimerically hermaphroditic, and are formed in vivo from the “parasitic” attachment of a “male” germ line embryo to a vestigial genital pore formed at the side of the head of a “female” germ line embryo. On contact, an enzyme digests the lips of the (attaching) mouth and the (attached to) pore. At this point, as blood vessels form, the circulatory systems of the pair fuse.
“Male” development then continues as follows: First, the attaching embryo forms and injects male gonadal stem cells, which migrate to colonize the (female) birth canal. Given appropriate hormonal triggers, these gonadal colonies form multiple testes, one or more of which may or may not produce viable sperm, and may or may not descend, depending upon various factors that affect hormonal regulators, including rank, age, courtship rituals, and nutritional status. Most commonly, multiple testes produce sperm, but none or one testis descends. Second, in response to hormonal and enzymatic triggers, the axial limb buds migrate dorsally, and continue growth as the “gripping” hand and arm—creating the “asymmetrical” physiognomy of the “upper” Swenson’s Apes.
Under specific circumstances, reproduction within a caste may proceed sexually, asexually, and/or chimerically. All Swenson’s Ape matings are spermatozoically competitive. During mating, the hermaphroditic pairs exchange sperm packets. Because of the chimerically redundant testes, these sperm packets may (and usually do) contain sperm from multiple germ lines. Sperm may be stored in special ducts for long periods, perhaps even years. This means that once a Swenson’s Ape has mated, under some conditions it is capable of continuing to bear offspring until its stored sperm is exhausted or dies. Because of the prevalence of hermaphroditic chimerism, all fertile Swenson’s Apes are also capable of self-fertilizing without ever mating at all, although this seems to be rare and has not been observed in the upper castes.
An additional factor accounts for previous reports of so-called “sex changing” in Swenson’s Apes. In the case of sexual reproduction, two Swenson’s Apes initially engage in elaborate courtship ritual and display, which stimulate associated hormonal production. At the end of this first phase, a bank of highly muscular sacs are excited and contract. These eject up to 144 chitonous “love darts,” similar to those produced by common land snails. Thereafter, sperm packets are exchanged.
Received packets are “split” by an enzymatic process that both triggers ovulation and dilates storage ducts, releasing stored sperm. All sperm—the recipient’s own, plus all lines within the received sperm packet— then “compete” to either re-enter storage, or ascend the birth canal and fertilize all available eggs. Sperm that do not reach the “safe haven” of a storage duct or an egg are scavenged by digestive enzymes. Conception normally results in multiple zygotes, for both parties.
However, the mucous coating on the “love darts” contains a powerful hormonal cocktail that blocks further production of androgenic (male) hormones and excites production of oogenic (female) hormones. This leads to retraction of the testis and growth of a placental bed, enabling embryonic implantation. At this point, given sufficient hormonal injection, a “darted” Swenson’s Ape becomes “female” for the purposes of gestation and birth. It is therefore theoretically possible for both Swenson’s Apes to become pregnant as a result of mating, but this has not been observed. The prevailing theory is that Swenson’s Apes sequester a significant proportion of available oogenic (female) hormone precursors in love dart mucous, thus rendering their bodies so depleted that they are unlikely to “receive as much as they give.” Thus, it may be a matter of chance that one or the other Swenson’s Ape will have further developed “love darts,” and thus have give up the chance at “being female.”
Where Have All the Flowers Gone?
At this point, we might well note: these creatures have a bizarre reproductive physiology. We might indeed ask: why!?
In the absence of any physical specimens, I can only speculate, but speculate I will. To begin, we must turn back to that basic foodstuff of the Swenson’s Apes: the “grasses” distributed thickly on the mudflats of the lower Oquirr delta. As is well noted, vegetation on New Utah is now sparse, but on first arrival our Founders reported vast, lush, green fields, glinting “almost aquamarine” in the long, sunny days. The “pastures” nourished man and beast alike: among its other ingredients, an old Founder’s soup recipe calls for “one measure marsh grass, dried and powdered.”