Upcoming Events

Evidence for the Orangutan Relationship

Home > Research :: Science Department > Current Research at the Buffalo Museum of Science > John R. Grehan > Human Origins and the Great Apes > Humans and Orangutan > Evidence for the Orangutan Relationship

Evidence for the orangutan being the closest living relative of modern humans is based on at least 35 known characters that appear to be either exclusive to humans and orangutans or largely absent in outgroups.

Literature on the evolutionary origins of humans and orangutans

Taxon comparaison: humans, orangutan, chimpanzee, gorilla (outgroups gibbon, monkeys) Characters and states from Grehan and Schwartz (2009) Evolution of the second orangutan: phylogeny and biogeography of hominid origins. Journal of Biogeography 36: 1823-1844.
No.	Character	Character Distribtion	Character status
1.	Scapula short and deep	Humans and orangutans: Shortest/deepest Coding:11000	Schwartz (1988), Groves (1987: 539). Robust Grehan and Schwartz 2009
2.	Supraspinous fossa	Humans and orangutans: most reduced Coding: 11000	Schwartz (1988: 197). Accepted by Groves (Grehan, 2006). Robust Grehan and Schwartz 2009
3.	Orientation of scapula spine	Humans and orangutans: most horizontal Coding: 11000	Schwartz 1988. Accepted by Groves (Grehan, 2006). Robust Grehan and Schwartz 2009
4.	Upward deflection of coracoid process	Humans and orangutans: Greatest Coding: 11000	Schwartz 1988. Accepted by Groves (Grehan, 2006). Robust Grehan and Schwartz 2009 Click here for scapula images
5.	Ethmo-sphenoid contact	Humans: 97%, Orangutans: 99% Chimpanzees: 77%, Gorilla: 50% Gibbons and monkeys: less or equal Coding: 11000	Presented in Schwartz 1988. Robust Grehan and Schwartz 2009
6.	Juvenile incisive foramen	Humans and orangutans: single Chimpanzees: weakly double Gorilla, gibbons, monkeys: double fenestrae Coding: 11000	Presented in Schwartz 1983,1988. Corroborated by Groves (1987: 539).Click here for details Robust Grehan and Schwartz 2009
7.	Foramen lacerum	Humans and orangutans: present Coding: 11000	Robust Grehan and Schwartz 2009
8.	Posterior palate thick	Humans and orangutans: thick Coding: 11000	Robust Grehan and Schwartz 2009
9.	Upper posterior deciduous molar protocone taller than paracone	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
10.	Lower posterior deciduous molar trigonid shortest	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
11.	Upper molar lingual shape	Humans and orangutans: oval Coding: 11000	Moderate Grehan and Schwartz 2009
12.	lower anterior deciduous molar protoconid anteriorly placed	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
13.	lower anterior deciduous molar mesially angled		Robust Grehan and Schwartz 2009
14.	lower anterior deciduous molar talonid basin closed	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
15.	Molar enamel thick	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
16.	Ischial callosities	Humans: and orangtuans: never Coding: 11000	Robust Grehan and Schwartz 2009
17.	Mamary gland/nipple distance between right and left gland as a percentage of chest breadth	Humans: 71%, Orangutans: 90% Chimpanzees: 52%, Gorilla: 46% Gibbons: 32%, Monkeys: 40% (narrow thorax)	Robust Grehan and Schwartz 2009
18.	Hairline receeded	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
19.	Hair orientation	Humans and orangutans: forward Coding: 11000	Robust Grehan and Schwartz 2009
20.	Beard and mustache developed	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
21.	Longest hair	Humans (head) and orangutans (body) yes Coding: 11000	Robust Grehan and Schwartz 2009
22.	Smile with closed lips	Humans and orangutans: yes Coding: 11000	Robust Grehan and Schwartz 2009
23.	estrogen production	Humans and orangutans: highest Coding: 11000	Robust Grehan and Schwartz 2009
24.	Estriol levels during mensrual cycle	Humans and orangutans highest Coding: 11000	Robust Grehan and Schwartz 2009
25.	Female initiated mounting	Humans and orangutans yes Coding: 11000	Robust Grehan and Schwartz 2009
26.	Radial vein present in forearm	Humans and orangutans yes Coding: 11000	Robust Grehan and Schwartz 2009
27.	Mechanical aptitude	Humans and orangutans: highest Coding: 11000	Robust Grehan and Schwartz 2009
28.	External ear helicies	Humans and orangutans: close Coding: 11000	Robust Grehan and Schwartz 2009
Derived (but not unique) features
.	Estrus cycle	1. Humans: absent 2. Orangutans: absent 3. Chimpanzees: present 4. Gorilla: present 5. Gibbons: present 6. Monkeys: present	Variable in monkeys, but inconsistently defined. Questioned by Groves (1987:540) due to zoo orangutans showing mid-cylce proceptivity. > Click here for details
	Anogenital tumescence during ovulatory cycle	1. Humans: absent 2. Orangutans: absent 3. Chimpanzees: present 4. Gorilla: present 5. Gibbons: present 6. Monkeys: sometimes absent?	Apparently absent in some monkeys, but poorly documented and often overlooked. Treated here as apomorphic for humans and orangutans. > Click here for details