Adrenarche

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Human Uniqueness Compared to "Great Apes": 
Speculative Difference
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Adrenarche is the postnatal onset of secretion of the androgen hormones dehydroepiandrosterone (DHEA) and DHEA-sulphate (DHEA-S) from the adrenal gland. Among the primates, these hormones are produced in a novel histological region called the zona reticularis. In humans and chimpanzees adrenarche occurs between the ages of 6 to 10 years. In some other primates, such as the rhesus monkey, the up-regulation of DHEA and DHEA-S begins peri-natally. Across primate species there are differences in the production of DHEA related with stage of development, social status, and gender, but little is known about systematic variation in adrenarche. DHEA acts as an anti-glucocorticoid wtih a wide variety of effects, including promoting immune function, altering glucose metabolism, and being neuroprotective, all suggesting a selective benefit. The evolutionary origins of adrenarche are not known. There is debate as to the relationship of adrenarche to puberty (pubarche). It is known that human adrenarche can result in the growth of some pubic and axillary hair, as well as changes in body odor. However, in humans the onset of adrenarche clearly precedes the increase of gonadal steroid secretion of puberty. In chimpanzees, the age at adrenarche and pubarche are more closely related. In humans, adrenache has been related to the adiposity rebound at the transition between the childhood and juvenile stages of the life cycle. Very little is known about the consequences of adrenarche for chimpanzee development. It is proposed that adrenarche and DHEA-S may play a role in hominoid evolution in terms of extended brain development and prolonged life span compared with other primates.

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
6,000 thousand years ago
Probable Appearance: 
3,500 thousand years ago
Definite Appearance: 
3,500 thousand years ago
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