The Great Apes

[Pckts]

Body mass in lowland gorillas: a quantitative analysis.
Zihlman AL1, McFarland RK.
Author information
Abstract
Body proportions and tissue composition (e.g., relative contributions of muscle, skin, bone, and adipose to total body mass) were determined through dissection of four adult captive lowland gorillas. The relative contribution of bone varies little among the four animals (10.2-13.4%) despite considerable range in body weights (99.5-211 kg). In tissue composition, three animals have on average 37.3% muscle relative to body mass. Maximum estimates of body fat range between 19.4-44%. Differences in age, sex, and life history events partially explain the observed variation in body proportions and tissue composition among the four animals. Although gorillas are considered extremely sexually dimorphic in body weight and canine size, differences in tissue are not as dramatic as body mass differences suggest. This study found sex differences mostly in the upper body; males have relatively heavier forelimbs, including heavier deltoid, trunk-binding, and deep back muscles compared to the younger female. The old, obese female had one half the muscle tissue of the other three animals (16% vs. 37.3%), and twice the body fat (44%); forelimbs and upper body musculature were relatively well-developed to compensate for the restricted hip-joint movement due to arthritis. Data on the variation in tissue composition and body proportions in gorillas provide a basis for comparison with other hominoids, including humans. For example, compared to highly dimorphic orangutans, gorillas have more muscle, less adipose tissue, lighter forelimbs and heavier hindlimbs. Such analyses complement studies of the skeleton and contribute to our understanding of human evolution and adaptation.
Copyright 2000 Wiley-Liss, Inc.
https://www.researchgate.net/publication...e_analysis

Most importantly is muscle distribution
Results
"In this study, our interest is in the gorilla
pattern of total body composition, i.e., the
proportion of bone, muscle, fat, and other
tissues relative to total body mass and their
distribution in the body. For this reason, we
do not report here on the weights of individ-
ual bones and muscles. Skeletal data are
the focus of another paper, and weights of
individual muscles are considered in a fu-
ture article that illustrates variation be-
tween species, using individual muscle
weights"

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

Bone distribution as % total body mass

 
Captive vs Wild
"It is likely that, on average, captive goril-
las are heavier and fatter than free-ranging
ones. Studies of human and nonhuman pri-
mate populations show that access to a rich
food source and decreased activity result in
heavier mass and higher body fat. For ex-
ample, monkeys who are provisioned or can
obtain human food remains or crops are de-
monstrably heavier (Mori, 1979; Strum,
1991; Altmann et al., 1993). Body fat is
rarely measured, but Altmann et al. (1993)
showed that baboons at Amboseli who ate
human food and traveled less were dramat-
ically fatter than their counterparts.
Parallel evidence in humans based on di-
rect measurement of body composition
shows that Europeans from the 19th cen-
tury were lighter in weight and had lower
body fat than the 20th century sample, pre-
sumably due to changes in diet and activity"
(Clarys et al., 1999).


"Orangutans. Like gorillas, orangutans
show marked sexual dimorphism in body
mass and linear measurements. In tissue
composition, gorillas and orangutans are
relatively comparable in amounts of bone
and skin. The striking difference in the two
species is in the relative proportions of mus-
cle and body fat. Healthy gorillas in our
sample have on average 37.3% muscle,
which exceeds that of the female orangutan
(27%) and that of the male (35%). In the
“other” category of tissue, which includes
body fat, organs, and the gastrointestinal
tract, gorillas at 35.4% are lower than oran-
gutans at 42.7%, suggesting a greater
amount of body fat or a heavier gastrointes-
tinal tract in orangutans.
In body proportions, gorillas have lighter
forelimbs than orangutans. In the hind-
limbs, female and male gorillas are compa-
rable (17.5% of total body mass vs. 17.3%),
whereas the female and male orangutan dif-
fer markedly from each other in their hind-
limb proportions (17.8% vs. 12.0%).
These comparisons suggest correlations
between the different behavioral ecology of
the two species. Lowland gorillas consume
foliage, fruit, and insects, feed and sleep in
trees or on the ground, and travel exclu-
sively on the ground (Tutin et al., 1991;
Remis, 1997a). They live in relatively cohe-
sive groups, usually with several adult
males, adult females, and young (Tutin,
1996; Remis, 1997b). Although there are dif-
erences in foraging and locomotion in fe-
male and male gorillas, they do not appear
to be marked.
Orangutans, in contrast, are highly arbo-
real and eat fruit, and adults are relatively
solitary while foraging (Galdikas, 1984,
1985, 1988). Females and males differ in
their arboreal travel, diet and foraging, so-
cial interactions, and caretaking of offspring
(Sujardito, 1982; Cant, 1987). Relative pro-
portions of muscle or body fat probably re-
late to a balance between locomotion and
the ability to store fat."


VS


Homo sapiens

"Homo sapiens. Clarys et al. (1999) sum-
marized the available data on direct mea-
surement of tissue composition based on 51
individuals (20 females, 31 males) compiled
over a 150-year period. The individuals had
known body weights, and absolute weights
recorded for skin, muscle, bone, and adipose
tissue. The subjects ranged in age from
16 –94 years; the average age for men was
56.6 years (SD 21.5), and for women, 75.5
years (SD 15.4). Body weights ranged from
38.5–97.2 kg in men, and from 32–75.4 kg in
women. Muscle relative to body weight av-
eraged 39.4% (SD 5.4%) in men; in women,
28.8% (SD 6%). Adipose tissue averaged
19.4% in men and 35.3% in women. For
men, the standard deviation was 9.6%, and
in women, 11.8%. The older age of the fe-
male subjects probably contributed to the
higher amount of adipose tissue, and lower
muscle mass.
The data on gorillas, orangutans, and hu-
mans suggest that hominoids have the abil-
ity to accumulate body mass, of which a
significant proportion is fat. Further analy-
sis of body composition in hominoids can
refine the species comparisons and so more
fully connect body composition and distribu-
tion to adaptation and evolutionary history." Reply