Human evolution: Thumbs up for efficiency

Modelling a muscle key to flexing the thumb, new study suggests that powerful opposability characterises dextrous human hand evolved in some of our fossil relatives about two million years ago — time when tool use became more important. If you have learned anything evolution or what makes it special, is likely something opposable thumbs. Our thumb indeed distinct its functional abilities, but not unique humans. All other apes and most African Asian monkeys also an which facilitates enhanced grasping abilities characterise all primates1Napier J.R. Prehensility hands primates.Symp. Zool. Soc. Lond. 1961; 5: 115-132Google Scholar. Thumb enabled by curved joint between base (first metacarpal) wrist (the trapezium) several muscles allow both flex abduct towards fingers. What special greater number size compared with apes, as well length, making easy for pads fingers connect2Napier The prehensile movements hand.J. Bone Joint Surg. 1956; 38: 902-913Crossref Google Scholar,3Marzke M.W. Precision grips, morphology, tools.Am. J. Phys. Anthropol. 1997; 102: 91-110Crossref PubMed Scopus (269) Together, this anatomy allows do forceful precision are considered critical remarkable manipulative now past3Marzke When why opposition arose during relationship been long-standing questions evolution, part due fragmentary record preserves little no information soft tissues. A issue Current Biology Fotios Alexandros Karakostis, Katerina Harvati colleagues4Karakostis F.A. Haeufle D. Anastopoulou I. Moraitis K. Hotz G. Tourloukis V. Biomechanics dexterity.Curr. Biol. 2021; 31: 1317-1325Abstract Full Text PDF (8) Scholar some, all, (hominins) around ago, at archaeological evidence reliance on butchery animals5Thompson Carvalho S. Marean C. Alemseged Z. Origins predatory pattern: transition large animal exploitation early hominins.Curr. 2019; 60: 1-23Crossref (38) evolutionary process wonderful ability produce multiple solutions same problem6Wainright P.C. Functional morphology ecological research.in: Wainright Reilly S.M. Ecological Morphology: Integrative Organismal Biology. University Chicago Press, Chicago1994: 42-59Google Previous research aiming reconstruct hominins has primarily focused bones, using skeleton ‘gold standard’ dexterity, assumption being closer recent humans, ability7Tocheri Orr C.M. Jacofsky M.C. Marzke history hominin since last common ancestor Pan Homo.J. Anat. 2008; 212: 544-562Crossref (156) Scholar,8Kivell T.L. Deane A.S. Tocheri Schmid P. Hawks Berger L.R. Churchill S.E. Homo naledi.Nat. Commun. 2015; 6: 8431Crossref (79) Karakostis argue ignores alternative biomechanical evolving including tissue solutions. Indeed, we look see variety different shapes sizes just bones (Figure 1). Australopiths 4–2 tend gracile first metacarpal limited markings (entheses) small, humans Neandertals7Tocheri In contrast, isolated metacarpals (2–1.8 old) from Swartkans, South Africa, may belong either Australopithecus Homo, robust shafts well-developed vary greatly shape7Tocheri Fast forward 1.5 naledi (∼250,000 contrasts shaft flared marking, remarkably wrist8Kivell aim understand significance morphological variation how relates quantifying bony modelling one opposition, opponens pollicis muscle. Using musculoskeletal modelling, their analysis simulates contraction taking into account robustness estimate amount force (torque) ‘biomechanical efficiency’ each specimen might produced opposing thumb4Karakostis absence preservation record, they model (large muscle, force) chimpanzee (small small force), offering extremes potential efficiency. find that, predictably, Neandertals show (i.e. high efficiency) (presumably) markings. However, unidentified Swartkrans specimens and, lesser extent, naledi, efficiency similar or, analyses, than despite having quite morphology. australopiths had less chimpanzees least intermediate them suggesting did enhanced, human-like australopith species associated behaviours9Backwell d'Errico F. Evidence termite foraging hominids.Proc. Natl. Acad. Sci. USA. 2001; 98: 1358-1363Crossref (165) Scholar, 10McPherron S.P. C.W. Wynn J.G. Reed Geraads Bobe R. Béarat H.A. stone-tool-assisted consumption tissues before 3.39 Dikika, Ethiopia.Nature. 2010; 466: 857-860Crossref (392) 11Harmand Lewis J.E. Feibel C.S. Lepre C.J. Sandrine Lenoble A. Boěs X. Quinn R.L. Brenet M. Arroyo et al.3.3-million-year-old stone tools Lomekwi 3, West Turkana, Kenya.Nature. 521: 310-315Crossref (430) Thus, appears individuals) (Australopithecus sediba) hominins. This correlates increased bone butchery5Thompson Why interesting? ways, those us (albeit there many) who spent long staring say these results come surprise: capacity species. if shape across specimens, H. 1), then consider comes within broader context (when preserved) distinctly skeletons, body brain sizes, geological contexts, question many times reasons. Much experimental behavioural clear importance tool-making tool-use12Marzke Shackley M.S. Hominid Pliocene Pleistocene: archaeology comparative morphology.J. Hum. Evol. 1986; 15: 439-460Crossref (110) 13Key A.J. Dunmore influence exerted non-dominant production.J. 78: 60-69Crossref 14Williams-Hatala E.M. Hatala K.G. Gordon Key Kasper Kivell manual pressures behaviors implications 2018; 119: 14-26Crossref (28) type, frequency complexity living primate relatives, species, subspecies populations15Rolian Tool manufacture Homo.in: Muller M.N. Wrangham R.W. Pilbeam D.R. Chimpanzees Human Evolution. Harvard Cambridge2017: 602-644Crossref There reason assume ability, own genus could evolved, perhaps parallel, among well. equally australopith, proficient users ago. As highlight, can be combinations outcomes. They demonstrated somewhat morphologies similarly only ten move act isolation16Marzke Toth N. Schick Reece Steinberg B. Hunt Linscheid An K.-N. EMG recruitment hard hammer percussion Oldowan 1998; 105: 315-332Crossref (99) Moreover, anatomical region hand. Hominins seemingly efficient generated increasing through compensatory adaptions palm. modern form necessarily be-all end-all take home message study4Karakostis Musculoskeletal risky business half data required preserved far direct marking itself17Williams-Hatala Hiles Rabey K.N. Morphology attachment sites does reflect architecture.Sci. Rep. 2016; 28353Crossref (23) mean such endeavours doomed failure. Historically palaeontologists put back burner lack evidence, obviously integral function reconstructing behaviour past. build models, adding muscles, improving understanding landmarks, incorporating shape, gain holistic range dexterity.