Certainty Style Key

Certainty styling is being phased out topic by topic.

Hover over keys for definitions:
True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Likely Difference
MOCA Domain: 
MOCA Topic Authors: 

The dementias are a group of conditions of which the principal feature is a loss of cognitive capacity, that is the ability to assimilate change in the environment. The conditions are acquired generally in old age, and thereby are distinguished from learning disabilities which are developmental. Dementias are also irreversible and by this feature are distinguished from the confusional states from which recovery may occur if the precipitating cause is removed. Disorientation in time and space is characteristic of the 'organic states' (dementias and confusional states), and memory failure is invariably present and usually progressive in the dementias. Much is known about the pathology of the dementias. In Alzheimer's disease, the commonest, there is accumulation of beta-amyloid protein which forms plaques within brain tissue, and the presennce of neuro-fibrillary tangles within neurones. There are also relatively selective neurotransmitter losses eg of the cholinergic and adrenergic projextions to the cerebral cortex. A number of predisposing genes are established of which by far the most important is ApoE. The presence of homozygocity for the ApoE4 allele substantially increases the individuals risk of suffering from Alzheimer dementia as also to a lesser extent does one E4 allele relative to the E3 and E2 alleles.

Changes resembling the plaques and tangles of Alzheimer dementia have been described in the great apes, but the changes are not nearly so severe as in the human condition and it is unclear whether there is cognitive loss.


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: 
200 thousand years ago
Definite Appearance: 
2 thousand years ago
Universality in Human Populations: 

Dementias occur in all human populations, probably with the same spectrum of pathology (transmissible dementias of the kuru type and wiith prion-related pathology eg in the Papua-New Guinea population, and the Parkinsonian-dementia syndrome of Guam being unusual exceptions).

Mechanisms Responsible for the Difference: 

The possibility  has to be considered that the organic dementias with their age-related and approximately uniform incidence across populations represent sapiens-specific variation that relates to the genetic change implicated in the transition from a hominid precursor eg H heidelbergensis or H antecessor.

Related MOCA Topics
Related Topics (hover over title for reason):
Referenced By:


  1. Tauopathy with paired helical filaments in an aged chimpanzee., Rosen, Rebecca F., Farberg Aaron S., Gearing Marla, Dooyema Jeromy, Long Patrick M., Anderson Daniel C., Davis-Turak Jeremy, Coppola Giovanni, Geschwind Daniel H., Paré Jean-Francois, et al. , J Comp Neurol, 07/2008, Volume 509, Issue 3, p.259-70, (2008)
  2. Apolipoprotein E variation at the sequence haplotype level: implications for the origin and maintenance of a major human polymorphism., Fullerton, S M., Clark A G., Weiss K M., Nickerson D A., Taylor S L., Stengârd J H., Salomaa V, Vartiainen E, Perola M, Boerwinkle E, et al. , Am J Hum Genet, 2000 Oct, Volume 67, Issue 4, p.881-900, (2000)
  3. Nucleus subputaminalis (Ayala): the still disregarded magnocellular component of the basal forebrain may be human specific and connected with the cortical speech area., Simić, G, Mrzljak L, Fucić A, Winblad B, Lovrić H, and Kostović I , Neuroscience, 1999 Mar, Volume 89, Issue 1, p.73-89, (1999)
  4. A beta40 is a major form of beta-amyloid in nonhuman primates., Gearing, M, Tigges J, Mori H, and Mirra S S. , Neurobiol Aging, 1996 Nov-Dec, Volume 17, Issue 6, p.903-8, (1996)
  5. Arginine residues at codons 112 and 158 in the apolipoprotein E gene correspond to the ancestral state in humans., Hanlon, C S., and Rubinsztein D C. , Atherosclerosis, 1995 Jan 6, Volume 112, Issue 1, p.85-90, (1995)