Parental Investment

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: 

Parental investment (PI) is defined within Life History Theory as the allocation of resources, such as time or energy, to offspring that incurs some cost to the parent. That cost is usually measured in terms of the benefits to a particular offspring which curtail the parent’s ability to invest in and produce other offspring. Some level of PI is found in all reproducing organisms, but PI is most costly in those species providing parental care behavior at pre-natal or post-natal stages of life, including egg guarding, preparation of nest, brood carrying, incubation, placental nourishment, and post-natal care including food provisioning, lactation, and protection of offspring. Parental care is found in species of invertebrates, fish, amphibians, reptiles, birds and mammals. PI for most primate species, including chimpanzees, bonobos, and orangutans, is typical for the mammals, in that female primates invest heavily both pre-natally and post-natally in the care and feeding of infants. In comparison, males of most primate species invest relatively little in offspring. Exceptions are the considerable male PI provided in species of marmosets and tamarins, Aotus (South American owl monkey), some macaques (e.g., Macaca sylvanus, the Barbary macaque), gorillas, and humans. In general, there is greater paternal PI with greater paternal certainty, e.g., paternal certainty is relatively low for chimpanzees but relatively high for gorillas. In contrast, the marmosets and tamarins practice polyandrous breeding (low paternal certainty) and the paternal PI may be a behavior to enhance mating opportunities. Humans in some cultures have, perhaps, the highest levels of paternal PI of all primate species. Humans also practice a unique form of biocultural cooperative breeding. Rules of marriage and kinship, as well as paternal certainty and enhancement of mating opportunities have been proposed to explain the human difference. The human style of PI may have begun to evolve with the appearance of Homo ergaster (Homo erectus) in the fossil record.


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: 
150 thousand years ago
Probable Appearance: 
100 thousand years ago
Definite Appearance: 
35 thousand years ago
The Human Difference: 

biocultural cooperative breeding

Universality in Human Populations: 

universal in all human populations


  1. Sex, love and oxytocin: Two metaphors and a molecule., C Carter, Sue , Neurosci Biobehav Rev, 2022 Dec, Volume 143, p.104948, (2022)
  2. Caring for infants is associated with increased reproductive success for male mountain gorillas, Rosenbaum, Stacy, Vigilant Linda, Kuzawa Christopher W., and Stoinski Tara S. , Scientific Reports, 2018/10/15, Volume 8, Issue 1, p.15223, (2018)
  3. Extraordinary intelligence and the care of infants., Piantadosi, Steven T., and Kidd Celeste , Proc Natl Acad Sci U S A, 2016 May 23, (2016)
  4. Comparative population genomics in animals uncovers the determinants of genetic diversity., Romiguier, J, Gayral P, Ballenghien M, Bernard A, Cahais V, Chenuil A, Chiari Y, Dernat R, Duret L, Faivre N, et al. , Nature, 2014 Nov 13, Volume 515, Issue 7526, p.261-3, (2014)
  5. The Evolution of Parental Care, Clutton-Brock, T. H. , Monographs in Behavior and Ecology, Princeton, p.352, (1991)
  6. Parental investment: The hominid adaptation, Lancaster, Jane B., and Lancaster Chet S. , How humans adapt: A biocultural odyssey, p.33–56, (1983)
  7. Parental investment and sexual selection, Robert, Trivers , Sexual Selection & the Descent of Man, Aldine de Gruyter, New York, p.136–179, (1972)