Knuckle-Walking and the Problem of Human Origins

Abstract

While the taxonomic affinity of man X and the African apes is generally undisputed, anthropologists have widely disparate opinions on the extent to which the common ancestors of man, chimpanzee, and gorilla resembled living pongids. Many authors proffer sketches of hominid evolution that include apelike stages (1), but few of these include details of the mechanisms whereby apelike forms evolved into more manlike apes which, in turn, culminated in man. Similarly, authors who suggest alternative theories that emphasize non-apelike precursors (2) have difficulty in delimiting the bio-' mechanical and environmental changes involved in the transition from preman to man.Several theories that have received special notice in discussions on human origins accentuate a "troglodytian" or great-ape stage immediately preceding the emergence of man, the plantigrade biped (1). In this article I assess the possibility of a troglodytian stage in human phylogeny in the light of recent behavioral and morphological studies on the hands of the great apes and man. Brachiationist TheoryIn his initial formulation of an evolutionary pathway that possibly culminated in man, Sir Arthur Keith pro-Circle No. 17 on Readers' Service Card posed three "stages": h3 lodytian, and plantigrac real quadrupedal monke evolved into "brachiatin apes that had a predilc pending themselves in o tures beneath brancher Keith's hypothetical hylc Keith also emphasiz in the second stage of I major difference betweer and "troglodytians" wa size of the latter.Man also is orthogra but instead of hanging a superstratum he stand a substratum.Keith and later brachi point to many features, the forelimb (upper lim that are shared by men example, the "brachiatoi have long arms relative t4 and long forearms in p second to fifth fingers; t table absolute size (but to total hand length in anteroposteriorly flatte strongly angled ribs; pro vertebral column into th a broad sternum, with p sion of the sternal elem4 long collarbones; should cated on the posterior z chest wall; large acromia the shoulder blades; late shoulder joints; considei SCIENCE of the shoulder and elbow joints; a relatively short truncal segment of the vertebral column-in particular, a short lumbar region; no tail; and a smaller ie coccyx and more sacral vertebrae than other anthropoid primates have (4).nsIn addition to the general bodily proportions and skeletal features listed above, the "brachiators" have in comto mon certain characteristics of soft parts that may be related to their semierect )n. and orthograde posturing. These include large muscles that raise the arm ttle and rotate the shoulder blade (5); a te characteristic arrangement of muscle fibers in the diaphragm; characteristic positions of the heart, lungs, and other organs in the body cavity; the close atylobatian, trog-tachment of some abdominal organs to le (3). Arbothe diaphragm and posterior abdominal y-like primates wall; a muscular pelvic diaphragm in ig" gibbon-like the pelvic outlet; and lumbar back Dction for sus-muscles that are sm...

Vectorial expansion of the involucrin gene and the relatedness of the hominoids.

“…There has been a long-continuing controversy as to whether the chimpanzee is more closely related to the human or to the gorilla. From their similarities in gross morphology and physiology, the chimpanzee and the gorilla were thought to be most closely related (10)(11)(12)(13)(14). Comparisons of the thermal stabilities of interspecific DNA hybrids (15), the sequence of Ti7-globin pseudogenes (16), the sequence of the intergenic DNA of the 3-globin gene cluster (17), and the mobility of cell proteins in two-dimensional electrophoresis (18) have favored a closer relatedness of the human and chimpanzee, whereas studies of mitochondrial DNA (19)(20)(21) have favored a closer relatedness of chimpanzee and gorilla.…”

Morphology of the Distal Radius in Extant Hominoids and Fossil Hominins: Implications for the Evolution of Bipedalism

“…At different times, the last common ancestor (LCA) has been reconstructed to have quite different locomotor repertoires based on traits in the forelimb. For instance, the LCA has been reconstructed to be a hylobatid-like brachiator (Keith, 1903), based on the retention of suspensory characteristics in the shoulder joint (Tuttle, 1969). Alternatively, it has been said to be an ''antipronograde,'' vertical-climber, based on convergence in wrist morphology of lorises and suspensory hominoids (Cartmill and Milton, 1977) and observational data on orangutan locomotion in terminal branches Thorpe et al, 2007).…”

Origin of human bipedalism: The knuckle-walking hypothesis revisited

“…At the time, Tuttle (1975) favored a phylogeny in which humans diverged prior to an orangutan/African ape clade, thus making a knuckle-walking ancestor of all great apes and humans very unlikely. Furthermore, the best early hominin fossil hand evidence at the time, the bones from several individuals collectively known as OH7, lacked any clear signs of knuckle-walking adaptations (Tuttle, 1969a). However, Tuttle (1969a) noted that the relevant metacarpal and radius morphology was not preserved.…”

“…The focus has shifted instead to whether bipedalism was preceded by exclusively or nearly exclusively climbing and suspensory behaviors (Tuttle, 1969aStern, 1975), including vertical climbing (Prost, 1980;Fleagle et al, 1981;Stern and Susman, 1981;Ishida et al, 1985;Senut, 1988), in a large-bodied ape, or whether the ancestral condition included a significant terrestrial (Gebo, 1996;Sarmiento, 1998), possibly knuckle-walking component (Washburn, 1967;Corruccini, 1978;Shea and Inouye, 1993;Begun, 1993aBegun, , 1994Strait, 2000, 2001d). Arguments for suspensory/ climbing ancestors ( Fig.…”