Photographic and Descriptive Musculoskeletal Atlas of Bonobos

First Detailed Anatomical Study of Bonobos Reveals Intra-Specific Variations and Exposes Just-So Stories of Human Evolution, Bipedalism, and Tool Use

“…This has been one of the most challenging and enduring quests faced by biological anthropologists, due to the very scarce number of bonobo specimens available in Western museums and zoos (Diogo and Wood, 2012). We published our detailed observations in an anatomical atlas of bonobos, which provides notes about variations as well as comparisons with humans, common chimpanzees, and other primates (Diogo et al, 2017b). As that atlas did not discuss the broader evolutionary implications of the obtained comparative data, the aim of the present short paper is to provide a discussion of those broader implications.…”

“…In contrast, there are many differences between bonobos and humans (right) concerning the presence/absence of muscles (shown in colors and/or with labels in the human scheme; muscles present in chimps and not in humans are shown in black, in chimps). Modified from Diogo et al (2017b); © Diogo has copyright of these figures.…”

“…As bonobos are obviously not fully bipeds (in fact, even their peculiar type of "bipedal walking" has been recorded as <1% of terrestrial locomotion in the wild: e.g., Doran, 1993), stating that the presence of this muscle is necessarily related to, and brought adaptative advantages for, human bipedalism (e.g., Lewis, 1989) does seem to be mainly an unsupported just-so-story. Similarly, the adductor pollicis accessorius, or "Henle" muscle of the hand, FIGURE 2 | Differences between forelimb muscles of common chimps, bonobos and humans, based and modified from Diogo et al (2017b). The only consistent difference between bonobos (center) and common chimps (left) concerning the presence/absence of muscles (shown in colors in the common chimps and bonobos schemes) is that in the former the intermetacarpales 1-4 are usually fused with the flexores breves profundi 3, 5, 6, and 8 to form the dorsal interossei muscles 1-4 (* in bonobo) figure, as is the case in humans.…”

“…Another assumption that is taken for granted is that our hand/forearm structures are highly derived, when compared to FIGURE 3 | Differences between hindlimb muscles of common chimps, bonobos and humans, based and modified from Diogo et al (2017b). The only consistent difference between bonobos (center) and common chimps (left) concerning the presence/absence of muscles (shown in colors in the common chimps scheme) is that the latter usually lack the scansorius, as is the case in humans.…”

“…Firstly, the facial expression muscle risorius (Figure 1) has been generally accepted as a unique feature crucial for the evolution of our FIGURE 1 | Differences between head muscles of common chimps, bonobos, and humans, based and modified from Diogo et al (2017b). There are no major consistent differences concerning the presence/absence of muscles in adult common chimps (left) and bonobos (center), the only minor difference (shown in gray in the common chimp scheme) being that the omohyoideus has no intermediate tendon in bonobos, contrary to common chimps (and humans).…”