Emotional Lacrimation (Crying)

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Human Uniqueness Compared to "Great Apes": 
Absolute Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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There are three types of lacrimation (shedding of tears, or "crying"): basal, reflexive, and psychic.  These types of tears can be differentiated by the stimuli that elicit them and their chemical composition.  While humans across the world produce psychic tears in response to both positive and negative emotions, and while similar emotions have been identified in other animal species, no reports exist of other animals showing psychic lacrimation.

Basal tears protect and lubricate the eyes, and are produced constantly.  Reflexive tears are produced in response to an acute irritant such as dust or dirt. Psychic tears, on the other hand, are produced during strong emotional responses (both positive and negative), and contain more of certain hormones (prolactin, adrenocorticotropic hormone, and leucine enkephalin).



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
Definite Appearance: 
100 thousand years ago
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The lacrimal system is rather complex. The lacrimal gland, the major source for tear production, is situated just above the eye. The lacrimal nucleus, the major source for innervating the lacrimal gland, is a subnucleus of the superior salivary nucleus in the tegmentum of the pons (part of the brain stem). The lacrimal nucleus receives projections from the autonomic nervous system as well as from various brain structures, including the frontal lobe, globus pallidus, thalamus, and hypothalamus. The projections from the frontal lobe are thought to be important in human psychic lacrimation.

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  2. Innervation of the lacrimal gland in the cynomolgous monkey: a retrograde tracing study., van der Werf, F, Baljet B, Prins M, and Otto J A. , Journal of Anatomy, 06/1996, Volume 188, Issue Pt 3, p.591 - 601, (1996)
  3. The lacrimal secretory system and its treatment., Jones, L T. , Am J Ophthalmol, 1966 Jul, Volume 62, Issue 1, p.47-60, (1966)