Dolicocephalinae

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The "Long-headed Hominids"

  • Class Mammalia
  • Subclass Placentalia
  • Order Primates
  • Family Hominidae
  • Subfamliy Dolicocephalinae
    • Elf - Hylocineta asterphila
    • Gnome - Gnoma albescens


Dolicocephalines are one of the two subfamilies of Family Hominidae. Their name means "long-heads" because their skulls are longer and narrower than those of the other subfamily, the eurycephalines. The two subfamilies of Hominidae represent two different strategies for dealing with the expanded, extended development of the brain.

Dolicocephalines accommodate the extended brain growth by being born at an very early stage of development compared to eurycephalines. Dolicocephaline infants are born after a comparatively short gestation period (about 200 days). At birth, infants weigh just 1 or 2 kilograms (about 3-5% of adult weight), with comparatively underdeveloped lungs, reflexes, and immune systems. Most significantly dolicocephaline infants are born with very soft, loose skulls that can accommodate a great deal of continued brain growth after birth. The cranial sutures (the gaps between the plates of the skull) remain apparent for 3.5 to 4 years. All this means that dolicocephaline infants require much more intensive care for their first several months of life, and continuing through several years.

The feature that gives the name of the dolicocephalines (their longer skull) is a secondary adaptation. Since dolicocephalines did not widen the birth canal and pelvic girdle as eurycephalines did, as dolicocephalines continued to evolve larger brains their skulls expanded in a mostly linear direction instead of the more globular skull expansion of the eurycephalines.

To take full advantage of the length-specific expansion, dolicocephaline fetuses are carefully oriented for birth by actions of both the fetus and by the uterus muscles so that the long head is aligned directly along the birth canal, and not across it.

Slight misalignment is not infrequent and easily correctable, so a birthing dolicocephaline mother is usually attended by at least one older relative. More severe misalignments (more than 20 degrees) are much rarer, and if it uncorrected are almost invariably fatal to the infant, and often to the mother. Even if such a misalignment is corrected midway through labor, the infant may have already sustained brain damage, abrasion of the spinal cord by vertebrae, or a broken neck. But other than this rare circumstance, dolicocephaline birthing is less dangerous then among eurycephalines.

However, a dolicocephaline infant requires more intensive care than a eurycephaline and is more delicate even compared to a eurycephaline infant conceived at the same time, and certainly compared to one born at the same time. Dolicocephaline infant mortality rates are significantly higher than those of eurycephaline under similar circumstances. Particular causes of infant mortality in dolicocephalines are a softer skull and lesser development of the heart and lungs and immune system at birth.

With such high investments into each infant, dolicocephalines practically never twin. The low rate of population replacement in dolicocephalines correlates with their long life spans, around a hundred years. With higher infant mortality, and lower birth rates, adult lifespans must be greater in order to maintain population sizes.

Because of the more intensive childcare, a dolicocephaline parent must be able to count on full commitment from its mate. Consequently dolicocephalines have a very strong pair-bonding drive and mate for life after long, often elaborate, courtships. Polygamy, though practiced by some eurycephalines, approaches being a physiological impossibility for dolicocephalines.

Due to their differences in reproductive strategy, dolicocephalines have much less sexual dimorphism than eurycephalines. The strong pair-bond and elaborate courtships influence this in two ways. First, direct male-male competition is reduced, so that males are closer in size to females. Secondly, the long courtships has meant that differences between females and males have not needed to be so apparent.

The strong pair-bond is a physiologically enforced characteristic, related to the distribution in the brain of receptors for sexual behavior hormones. This creates a strong physiological/emotional association between a specific individual and sexual behavior (sexual behavior defined very broadly). As implied above, the pair-bond comes into existence gradually over a lenghty courtship process.

Pair-bonding is a trigger to significant parts of puberty. On the most direct and simple level, the late stage development of the pair-bond triggers the hormone signals that lead to full, adult development of sexual anatomy and behavior. On a subtler level, the process of pair-bonding at several stages triggers periods of brain growth and/or re-organization. Eurycephalines have a brain growth spurt at the beginning of puberty, providing the raw material for new neural pathways to process new behaviors. Dolicocephalines have a smaller spurt at the beginning of adolescence (at the time when courtship behavior first starts happening), and another, larger, one late in the process.

Most dolicocephaline cultures only consider individuals who have completed pair-bonding to be adults. This reflects, but often overstates, an underlying biological reality that the unbonded lack the final stages of brain growth that a normal, bonded individual has undergone. Most dolicocephaline cultures do not have a strong stigma against same-sex bondings. Though the principals are similarly non-reproductive, they do experience the full developmental pathways of other bonded individuals.

Since brain and body development occur in feedback with the behavioral processes of pair-bonding, failure in a bond (usually due to the untimely death of one of the principals) can cause a range of developmental abnormalities, particularly if it occurs late in the process. Effectively, growth patterns are initiated, but the later pieces and directions are never supplied.


This article has Design Notes: Dolicocephalinae/Notes

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