Given our inherent human-centric viewpoint, we tend to think that our species is more advanced in all respects than other animals, but new research finds that human hands are more primitive than those of our closest primate ancestors: chimpanzees. 
 
 The study, published in the latest issue of the journal Nature Communications, determined that while human hand proportions have changed little from those of the last common ancestor of chimps and humans, the hands of chimps and orangutans have evolved quite a bit. 
 
 Prehistoric Moms Had Their Hands Full: Photos 
 
 “The findings suggest that the structure of the modern human hand is largely primitive in nature, rather than, as some believe, the result of more recent changes necessary for stone tool-making,” Kurtis Hiatt, a spokesperson for The George Washington University, told Discovery News. 
 
 Sergio Almécija, a scientist in the university’s Center for the Advanced Study of Human Paleobiology, led the study, which was co-authored by Jeroen Smaers and William Jungers. Smaers and Jungers are researchers at Stony Brook University, where the research was conducted. 
 
 The researchers came to their conclusions after analyzing the hands of humans, chimps and orangutans, as well as the remains of hands for early apes like Proconsul heseloni and the hands of human ancestors, such as Ardipithecus ramidus and Australopithecus sediba. 
 
 Almécija and his team discovered that human hands today are not that different from those of the early human ancestors. 
 
 “Human hands are marked by a relatively long thumb when compared to the length of their four other fingers — a trait that is often cited as one of the reasons for the success of our species because it facilitates a ‘pad-to-pad precision grip,’” Hiatt said. 
 
 Conversely, chimp hands are much longer and narrower. Since the thumb is not as long, it just meets up with the palm, while the chimp’s other four fingers extend upward. As a result, chimps and orangutans do not have opposable thumbs as we do. 
 
 Like Humans, Chimps Tend to Be Right-handed 
 
 Gorillas also appear to have inherited our more primitive hand structure. Like human hands, gorilla hands have five fingers, including an opposable thumb. Gorilla feet are similar to ours too. Each gorilla foot has five toes, but their big toe is opposable and can move much more flexibly than ours can. 
 
 Almécija and his colleagues suspect that all living primates survived a late Miocene (12 to 5 million years ago) extinction event by specializing to exist in certain habitats. While chimps and orangutans became tree-climbing specialists, humans evolved to become more terrestrial. Gorillas did too. 
 
 While we tend to think that gorillas spend much of their time hanging around in trees, the truth is that they only spend about 5 to 20 percent of their time in trees. Even then, the tree scaling is just to escape threats or to forage for food. 
 
 The new study challenges the assumption that the evolution of a more “sophisticated” hand in humans first appeared in the common ancestor of chimps and our species. Our hands, however useful, may instead represent a very primitive anatomical structure that’s been around for millions of years. 
 
 Photos: Left, human hand; Credit: Sergio Almécija 
 
 Right, chimpanzee hand; Credit: Credit: Michele W, Flickr ||||| Intrinsic hand proportions 
 
 Hand proportions of humans are usually compared with those of apes using the thumb-to-digit ratio (or IHPs), which is a good functional measure of thumb opposability and therefore a proxy for manual dexterity (for example, refs 1, 14, 19). Accordingly, we queried our anthropoid sample (see details of our sample in Supplementary Table 1) to see whether our IHP measure (as revealed by the thumb-to-fourth ray ratio; Fig. 1b) was consistent with previous observations that humans can easily be distinguished from modern apes by a long thumb relative to the other digits4, 5, 14. The modern human IHP range is well above that of modern apes (that is, no overlap; analysis of variance (ANOVA) with Bonferroni post hoc comparisons, P<0.001; see Supplementary Table 2 for details on the taxa-specific comparisons), which can be linked directly to the human capability (unique among modern hominoids20) to perform an efficient ‘pad-to-pad precision grasping’ (that is, broad contact of the distal pads of the thumb and index finger, Supplementary Note 1)1, 4, 5, 13. In contrast, chimpanzees and especially orangutans are found to have significantly shorter thumbs than gorillas and hylobatids (ANOVA with Bonferroni post hoc comparisons, P<0.001). Fossil hominins fall within the modern human range, but Ar. ramidus exhibits a shorter thumb (within the gorilla-hylobatid range), implying limits to its precision grasping capabilities. Most non-hominoid anthropoids, including the fossil ape Pr. heseloni, exhibit IHP ranges in-between modern apes and humans. Both Cebus and Theropithecus overlap in this index with humans, supporting the relationship between this ratio and enhanced manipulative skills (see Supplementary Note 1). 
 
 Extrinsic hand proportions 
 
 Despite the aforementioned functional connections, IHPs provide limited information regarding what distinguishes humans from apes: is it a longer thumb, shorter digits or a combination of both? More specifically, which elements contribute most to the overall ray length? To clarify this and inspect how each of the individual elements of the thumb and ray IV contribute to IHPs (Fig. 1b), we standardized each length relative to overall body size (approximated by the cube root of its body mass, BM), creating relative length shape ratios of external hand proportions (EHPs; Supplementary Fig. 1). Major trends of EHP variation between the individuals in our anthropoid sample are summarized and inspected by means of principal components analysis of extant and fossil individuals (Supplementary Table 3), revealing high EHP heterogeneity in extant hominoids (and in non-hominoid anthropoids; Fig. 2a, Supplementary Fig. 1). In other words, there is a clear EHP structure that allows the characterization of the hominoid taxa. Statistical differences in EHP between each great ape genus, hylobatids and humans were established (P<0.001) by means of multivariate analysis of variance (MANOVA with Bonferroni-corrected post hoc pairwise comparisons; see Supplementary Table 4). Differences among extant great ape genera are more apparent when the eigenanalysis is carried out exclusively on great ape individuals (Supplementary Fig. 3), even revealing significant differences between species of gorillas (P=0.014) and chimpanzees (P=0.047). EHPs of selected species are depicted to help understand extreme morphologies along the major axes of variation in shape space (Fig. 2b). A complex pattern is revealed: hylobatids, orangutans and chimpanzees (in this order) exhibit longer digits than humans, but gorillas do not. Thumb length follows a rather different trend: hylobatids have both the longest digits and the longest thumbs, whereas Theropithecus displays the shortest digits but not the shortest thumbs (rather, eastern gorillas do). For Ar. ramidus we inspect two different relative shape possibilities based on substantially different but plausible BM estimations: 50.8 kg (as a quadruped) and 35.7 kg (as a biped). Fossil hominins display a modern human pattern, but Ar. ramidus shows only slightly longer or shorter (BM-depending) digits than Pr. heseloni (that is, it is intermediate between humans and chimpanzees), but in both cases it exhibits shorter thumbs (specifically shorter pollical phalanges; Supplementary Table 3) than this fossil ape and other hominins, and occupies a different region of EHP shape space (Fig. 2 and Supplementary Fig. 2). The observed differences in EHP between hominoid taxa cannot be merely attributed to size-dependent effects (that is, allometry; Supplementary Fig. 4, Supplementary Table 5). 
 
 Figure 2: Extrinsic hand proportions of humans and other anthropoid primates. (a) Principal components analysis of the body mass-adjusted hand lengths. (b) Summary of the contribution of each hand element in selected anthropoids. Species are arranged by maximum length of ray IV (notice that the thumb does not follow the same trend). ARA-VP-6/500 L refers to an iteration of Ar. ramidus with an estimated body mass of 50.8 kg, whereas ARA-VP-6/500 S uses a smaller estimate of 35.7 kg. Full size image (74 KB) Previous 
 
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 The evolution of human and ape hand proportions 
 
 Previous observations on modern ape thoraces and limbs suggest that living apes show similar but not identical adaptations to accommodate similar functional demands related to specialized climbing and suspension (especially Pan and Pongo), reinforcing the role of parallelism in ape evolution3, 21, 22, a phenomenon explained by common evolutionary developmental pathways in closely related taxa23. To test this homoplastic hypothesis for similarities in hand-length proportions between suspensory taxa, we enlist the ‘surface’ method24, which allows inferring the history of adaptive diversification in hominoids (and other anthropoids) using a phylogeny (Fig. 3) and phenotypic data, in this case the two major axes of EHP variation among extant and fossil species (accounting for 94.5% of variance; see Fig. 4 and Supplementary Table 7). This method models adaptive evolutionary scenarios by fitting a multi-regime Ornstein Uhlenbeck (OU) stabilizing selection model25 to the tip data. This procedure allows taxonomic units to undergo shifts towards different phenotypes (‘adaptive peaks’) and can be used to identify cases where multiple lineages have discovered the same selective regimes (that is, convergence). Regimes are here understood as comprising a group of taxonomic units that are inferred to have similar phenotypes. Adaptive peaks can be understood as the optimal phenotypic values that characterize the different regimes. The advantage of the surface method is that it locates regime shifts without a prior identification of regimes. The method hereby fits a series of stabilizing selection models and uses a data-driven stepwise algorithm to locate phenotypic shifts on the tree. Thus, this method allows to ‘naively’ detect instances of phenotypic convergence in human and ape hand proportions. Starting with an OU model in which all species are attracted to a single adaptive peak in morphospace, ‘surface’ uses a stepwise model selection procedure based on the finite-samples Akaike information criterion (AICc)26, 27 to fit increasingly complex multi-regime models. At each step, a new regime shift is added to the branch of the phylogeny that most improves model fit across all the variables inspected, and shifts are added until no further improvement is achieved. To verify true convergence, this method then evaluates whether the AICc score is further improved by allowing different species to shift towards shared adaptive regimes rather than requiring each one to occupy its own peak. For the EHPs, ‘surface’ detects five adaptive optima (see edge colours in phylogenetic tree in Fig. 3) corresponding to (1) Cebus and Alouatta; (2) Papio and Theropithecus; (3) Macaca, Mandrillus, Nasalis, Gorilla and hominins; (4) hylobatids; and (5) Pan and Pongo. In other words, in terms of human and great ape evolution ‘surface’ identifies convergent evolution between the EHPs of Pan and Pongo, whereas Gorilla and hominins share a more plesiomorphic condition for catarrhines. To verify this result, we compare the statistical fit of this evolutionary scenario with that of five other evolutionary hypotheses based on the respective relative AICc weights (Supplementary Fig. 5; Supplementary Table 8). The alternative models include Brownian motion evolution, a single-regime OU model, a multi-regime OU model differentiating the different clades, and most importantly an alternative version of the five-regime OU model detected by ‘surface’ in which the condition shared by Pan and Pongo is hypothesized to represent the plesiomorphic state for great apes (OU5 ‘alt’ in Supplementary Fig. 5). Our results support the ‘surface’ output as the best fit model using either a large or a small body size estimate for Ar. ramidus (ΔAIC c =0.00, AIC c weight=1.00), and even when excluding Ar. ramidus and Pr. heseloni from the analysis (ΔAIC c =0.00, AIC c weight=0.77). To test the sensitivity of our results to a possible sampling bias due to the higher number of hominoid species in comparison with monkey clades in our sample, we repeat the analysis once more after excluding the most speciose and morphologically derived group of hominoids (the hylobatid species), together with the fossil closest to the hominoid LCA in our sample (that is, Pr. heseloni). Again, ‘surface’ identifies a best fit model in which Pan and Pongo are convergent, with the difference that the slightly reduced digits of gorillas and hominins are now interpreted as being convergent with baboons, while the remaining monkey taxa share a common, more plesiomorphic, regime (Supplementary Fig. 6). This evolutionary scenario also has the best support (ΔAIC c =0.00, AIC c weight=0.92) when compared with Brownian motion, and four other alternative evolutionary scenarios (Supplementary Table 8). Importantly in terms of human and ape evolution, irrespective of the difference in results between the full vs reduced hominoid sample, the similarities between the EHP of hominins and gorillas are reconstructed as representing the plesiomorphic condition for the African ape and human clade (Fig. 3), while Pan would be more derived (and convergent with Pongo). 
 
 Figure 3: Time-calibrated phylogenetic tree showing the estimated adaptive regimes in our anthropoid sample. Adaptive optima are based on the two major axes of extrinsic hand proportions (EHP) variation between extant and fossil species (accounting for 94.5% of the variation). Branches are colour-coded according to different adaptive regimes (revealing that Pan and Pongo -red edges- are convergent). Clades are colour-coded (circles) as follows: brown, platyrrhines; dark green, cercopithecids; purple, hylobatids; light green, orangutans; red, gorillas; orange, chimpanzees; pink, fossil hominins; light blue, modern humans. The nodes corresponding to the last common ancestor (LCA) of great apes-humans and chimpanzees-humans are highlighted. Full size image (141 KB) Previous 
 
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 Figure 4: The evolutionary history of human and ape hand proportions. Phylomorphospace projection of the phylogeny presented in Fig. 3 onto the two first principal components (PCs) of extrinsic hand proportions (EHP) in extant and fossil species. Taxa are colour-coded as in the phylogenetic tree; internal nodes (that is, ancestral-states reconstructed using maximum likelihood) are also indicated, highlighting the positions in shape space of the great ape-human and chimpanzee-human LCAs (plus 95% confidence intervals for the latter estimate). (a) EHP of Ardipithecus ramidus estimated using 50.8 kg. Owing to space constrictions, macaque species are not labelled. (b) Iteration using 35.7 kg for Ar. ramidus. Outlines (scaled to similar length) of extant and fossil apes and Ar. ramidus are plotted in this phylomorphospace to help visualizing major shape changes occurred during ape and human hand evolution. Panels (c) and (d) depict the EHP of chimpanzees and humans vis-à-vis their reconstructed last common ancestor (LCA) assuming, respectively, 50.8 kg and 35.7 kg for Ar. ramidus. Full size image (118 KB) Previous 
 
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 Furthermore, to visually track major evolutionary changes driving differences between apes and humans, we summarize the evolutionary history of hominoid hand length diversification (as compared with platyrrhine and cercopithecid monkey out-groups) by means of a phylomorphospace approach28. These are the steps that we followed: First, we reconstructed hypothetical ancestral morphologies (that is, internal nodes in Fig. 3) using a maximum likelihood approach and plotted them on the shape space defined by the two major EHP axes of variation among extant and fossil species (Fig. 4). Second, we mapped our time-calibrated phylogenetic tree (Fig. 3) onto this shape space by connecting the ancestral sate reconstructions and the terminal taxa. The lengths and orientations of the branches of this phylomorphospace allows one to intuitively visualize the magnitude and directionality of inferred shape changes along each branch of the tree. Owing to the possible impact of Ar. ramidus in the reconstruction of the chimpanzee-human LCA (based on its proximity in time), we present this analysis with both large and small body size estimates (Fig. 4a,b respectively), as well as by excluding Ar. ramidus and Pr. heseloni (Supplementary Fig. 7). In all cases, major evolutionary changes along PC1 (~86% of variance; see Supplementary Table 7) relate to digital (primarily metacarpal and proximal phalanx) lengthening/shortening (positive and negative values, respectively), whereas PC2 (~8% of variance) relates to thumb proximal phalanx (positive values) and digital metacarpal (negative values) lengthening, and thereby serves to separate our platyrrhine and catarrhine taxa (especially baboons). Although the position of Ar. ramidus in shape space differs depending on estimated BM, the overall evolutionary pattern remains constant: from moderate digital length, digital lengthening has been achieved to different degrees and independently in chimpanzees, orangutans and hylobatids (in this increasing order; with Pan and Pongo sharing the same adaptive optimum, see Fig. 3). In contrast, hominins and gorillas (especially eastern gorillas) have slightly reduced their digital lengths (although both would still represent the same evolutionary regime, see Fig. 3). In terms of thumb evolution, only a modest reduction in extant great apes and slight elongation in later hominins appears to have occurred. It is worth noticing that, irrespective of which Ar. ramidus BM estimate is used, Pan falls clearly outside of the 95% confident interval for the estimated chimpanzee-human LCA, whereas Ar. ramidus is very close to it (Fig. 4), as previously suggested2, 29. This supports the idea that chimpanzees exhibit derived hands, in this case convergent with Pongo (Fig. 3). 
 
 This previous phylogenetic patterning observed in our EHP morphospace (that is, homoplasy along PC1, and more clade-specific groups along PC2; see Fig. 4) was tested with Blomberg’s K statistic30. Our results indicate that for PC2 variance is concentrated among clades (K>1; 1,000 permutations, P=0.001): Alouatta (long thumb proximal phalanx and short digital metacarpal) and baboons (reverse condition of howler monkeys) are situated at opposite extremes, and other cercopithecids and hominoids exhibit intermediate values. For PC1, however, the variance is concentrated within clades (K<1; 1,000 permutations, P=0.001), indicating that the observed variance in finger length (that is, PC1) is larger than expected based on the structure of the tree. This supports the idea of adaptive evolution (that is, shape change associated with change in function)31 in hominoid finger length uncorrelated with phylogeny30. In other words, finger lengthening has been achieved homoplastically in different ape lineages (probably in relation to increased suspensory behaviours), as also revealed by our multi-regime OU modelling (Fig. 3, Supplementary Figs 5 and 6) and phylomorphospace approach (Fig. 4). 
 
 To inspect how the addition of more taxa with long fingers affects our evolutionary reconstructions of digital length, we revisit the phylomorphospace after excluding the thumb elements. Specifically, we incorporate the fossil ape Hispanopithecus laietanus17 (which does not preserve thumb elements; Fig. 5a–c) and the suspensory platyrrhine Ateles (which exhibits only a vestigial thumb32). Hi. laietanus represents the earliest evidence of specialized adaptations for below-branch suspension in the fossil ape record17, 33. However, its phylogenetic position is not resolved, being alternatively considered as a stem great ape, a stem pongine or even a stem hominine (Fig. 5d–f). In the fourth ray morphospace (Fig. 6), PC1 (~92% of variance; Supplementary Table 7) is mainly related positively to metacarpal and proximal phalanx lengths, whereas PC2 (~6% of variance) is positively related to metacarpal length and negatively to proximal phalanx length. When ancestral state reconstructions and phylogenetic mapping are inspected in this phylomorphospace, the overall evolutionary pattern reflecting homoplasy in modern (and fossil) ape digital elongation is also evident, irrespective of the BM estimate of Ar. ramidus and the phylogenetic position of Hi. laietanus (Fig. 6). Specifically, these results also indicate independent digital elongation (to different degrees) in hylobatids, orangutans, chimpanzees, spider monkeys and Hi. laietanus. Although chimpanzees and Hi. laietanus exhibit a similar relative digital length (Supplementary Fig. 4b), it has been achieved by different means. In contrast to chimpanzees and baboons that display long metacarpals relative to proximal phalanges (as revealed by PC1 in Fig. 6), Hi. laietanus approaches a condition similar to that of howler monkeys by exhibiting long phalanges relative to short metacarpals (as revealed by PC2 in Fig. 6). Overall, these results match the previously recognized mosaic nature of the Hi. laietanus hand morphology17, which suggests that its suspensory-related adaptations evolved independently from that of other apes. More broadly, even though the living hominoid lineages represent the few remnants of a much more prolific group during the Miocene22, the evidence presented above indicate that hominoids constitute a highly diversified group in terms of hand proportions (as identified in Fig. 2, Supplementary Fig. 1, and Figs 4 and 6). 
 
 Figure 5: The hand of the late Miocene ape Hispanopithecus laietanus. Its reconstructed hand is displayed in dorsal (a) and palmar (b) views, and together with its associated skeleton (c). This species represents the earliest specialized adaptations for below-branch suspension in the fossil ape record33, although its hand combining short metacarpals and long phalanges, dorsally oriented hamato-metacarpal and metacarpo-phalangeal joints, presents no modern analogues17. The phylogenetic position of Hispanopithecus is still highly debated: stem great ape (d), stem pongine (e) or stem hominine (e)? Scale bars represent 10 cm. Reconstruction of the IPS 18800 (Hispanopithecus) skeleton in panel (c) reproduced with the permission of Salvador Moyà-Solà and Meike Köhler. Full size image (256 KB) Previous 
 
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 Figure 6: Reconstructed evolutionary histories of human and ape digital extrinsic proportions. The phylomorphospace approach was limited to the three long bones of ray IV to include the fossil ape Hispanopithecus laietanus and Ateles species. The same analysis was iterated with the large (a) and small (b) body mass estimates of Ardipithecus ramidus (finding no differences in the overall evolutionary pattern). Internal nodes (that is, ancestral-state reconstructions) and branch lengths are indicated for three different phylogenetic hypotheses: Hi. laietanus as a stem great ape (black), a stem pongine (orange) and stem African ape (red). Species names are indicated in (a) with the exception of macaques. Full size image (132 KB) Previous 
 
 Figures index ||||| The human hand is a marvel of dexterity. It can thread a needle, coax intricate melodies from the keys of a piano, and create lasting works of art with a pen or a paintbrush. Many scientists have assumed that our hands evolved their distinctive proportions over millions of years of recent evolution. But a new study suggests a radically different conclusion: Some aspects of the human hand are actually anatomically primitive—more so even than that of many other apes, including our evolutionary cousin the chimpanzee. The findings have important implications for the origins of human toolmaking, as well as for what the ancestor of both humans and chimps might have looked like. 
 
 Humans and chimps diverged from a common ancestor perhaps about 7 million years ago, and their hands now look very different. We have a relatively long thumb and shorter fingers, which allows us to touch our thumbs to any point along our fingers and thus easily grasp objects. Chimps, on the other hand, have much longer fingers and shorter thumbs, perfect for swinging in trees but much less handy for precision grasping. For decades the dominant view among researchers was that the common ancestor of chimps and humans had chimplike hands, and that the human hand changed in response to the pressures of natural selection to make us better toolmakers. 
 
 But recently some researchers have begun to challenge the idea that the human hand fundamentally changed its proportions after the evolutionary split with chimps. The earliest humanmade stone tools are thought to date back 3.3 million years, but new evidence has emerged that some of the earliest members of the human line—such as the 4.4-million-year-old Ardipithecus ramidus (“Ardi”)—had hands that resembled those of modern humans rather than chimps, even though it did not make tools. And back in 2010, a team led by paleoanthropologist Sergio Almécija, now at George Washington University in Washington, D.C., began arguing that even earlier human relatives, dating to 6 million years ago—very soon after the human-chimp evolutionary split—already had humanlike hands as well. This even included the ability to press the thumb against the fingers with considerable force, a key aspect of precision gripping. 
 
 To get a grasp on what early hands really looked like, Almécija and his colleagues analyzed the thumb and finger proportions of a large number of living apes and monkeys, including modern humans. They then compared these to the hands of several extinct species of apes and early humans, including Ardi, the Neandertals, and the 2-million-year-old Australopithecus sediba from South Africa, which its discoverers controversially think might be a direct ancestor of humans. The sample also included the 25-million-year-old fossil ape known as Proconsul. 
 
 The team crunched the measurements from all these samples using sophisticated statistical methods designed to determine the course of hand evolution over time. The researchers found that the hand of the common ancestor of chimps and humans, and perhaps also earlier ape ancestors, had a relatively long thumb and shorter fingers, similar to that of humans today. (Gorillas, which spend most of their time on the ground and not in trees, have similarly shaped hands.) Thus, the human hand retains these more “primitive” proportions, whereas the elongated fingers and shorter thumbs of chimps, as well as orangutans, represent a more specialized and “derived” form ideal for life in the trees, the team reports today in Nature Communications. 
 
 Almécija says that a hand capable of precision grasping was “one of the earliest adaptations” among members of the human line, possibly because it made our ancestors better at gathering a wider variety of foods, and not originally because it made them better toolmakers. And if human hands largely retained the “primitive” state, he adds, the most important changes that led to toolmaking would have been “neurological” -- that is, the result of the enlargement and evolution of the human brain and its ability to plan ahead and better coordinate hand movements. 
 
 “Their results fit very nicely with the view … that the human hand is best described as primitive,” says Tracy Kivell, an anthropologist at the University of Kent in the United Kingdom who specializes in the study of the primate hand and wrist. “It’s good to see that some of the implications of Ardi”—that the common ancestor of chimps and humans was not chimplike—“are being noticed,” adds Owen Lovejoy, an anatomist at Kent State University in Ohio and member of the team that studied this early member of the human line. Rather than being a good model for this common ancestor, Lovejoy says, today’s chimps are “highly specialized” for a fruit-eating life high up in the trees. 
 
 But the study is not likely to receive a warm welcome from researchers who think the common ancestor of chimps and humans was indeed more chimplike. The team “build[s] an evolutionary scenario based on one data point, bony proportions of hands, with the underlying assumption that they tell a story,” says Adrienne Zihlman, a primatologist at the University of California, Santa Cruz. Zihlman argues that the hands alone provide researchers with only a very limited view of what the common ancestor was like. “This paper serves as a poster child for what is wrong with a lot of work in paleoanthropology.” ||||| Scientists in the United States and Spain said the human hand may be more primitive than that of our closest living cousin, the chimpanzee Strong fists for defending ourselves and opposable thumbs for work as fine as threading a needle—hand specialisation is widely believed to have given humans a major evolutionary advantage. 
 
 On Tuesday, scientists in the United States and Spain said the human hand may be more primitive than that of our closest living cousin, the chimpanzee. 
 
 In fact, human hands are likely more similar to those of the last common ancestor we and chimps shared millions of years ago. 
 
 "These findings indicate that the structure of the modern human hand is largely primitive in nature, rather than the result of selective pressures in the context of stone tool-making," said a press summary from the journal Nature Communications, which published the study. 
 
 In fact, it is the hands of chimps and orangutans that changed most since they split off to form new branches of the hominid family tree—developing longer fingers, compared to the thumb, for swinging on tree branches. 
 
 The human hand has a longer thumb relative to the other fingers than that of chimps and other apes—allowing for what scientists call "pad-to-pad" precision grasping, which simply means that our fingertips are able to touch. 
 
 There is a widely held assumption among palaeontologists that the last common ancestor (LCA) of humans and apes, an individual whose identity remains uncertain, was a prototype chimp with chimp-like hands. 
 
 But a team led by Sergio Almecija of The George Washington University's Center for the Advanced Study of Human Paleobiology, is challenging that. 
 
 They analysed the hand-length proportions of humans, as well as living and fossil apes to draw a picture of the evolutionary history, and found the human "thumb-to-digits ratio required little change since the LCA." 
 
 "The inevitable implication is that when hominins (the extended human family excluding apes) started producing flaked stone tools in a systematic fashion, probably as early as 3.3 million years ago, their hands were—in terms of overall proportions—pretty much like ours today," Almecija told AFP by email. 
 
 "Another important take-home message is that if human hands are largely primitive, the 'relevant' changes promoting the emergence of widespread reliance on stone tool culture were probably neurological" and not manual—meaning it was our brains that allowed for adaptation. 
 
 "Any evolutionary model of human hand evolution assuming a chimpanzee-like ancestor will likely be flawed from the beginning," he added. 
 
 Explore further: Human ancestor was less-chimp-like than thought: study 
 
 More information: Nature Communications, DOI: 10.1038/ncomms8717 
 

– Consider yourself more advanced than a chimpanzee? When it comes to your hands, at least, you might be wrong. American and Spanish researchers who studied the hands of chimps, orangutans, humans, as well as those of human ancestors and ancient apes, say a chimp’s hands have evolved significantly since humans and chimps diverged on the evolutionary path some 7 million years ago. Initially displaying a long thumb and shorter fingers, chimp and orangutan fingers elongated to allow them to swing among the trees, reports AFP. But human hands—with a long thumb for grasping objects—have changed little over millions of years, a Nature study finds. When early humans "started producing flaked stone tools in a systematic fashion, probably as early as 3.3 million years ago, their hands were—in terms of overall proportions—pretty much like ours today," explains study author and George Washington University scientist Sergio Almécija. Almécija suggests the hands of early humans as far back as 6 million years ago may have been similar as well, Science reports. The whole idea challenges the long-held view that our earliest ancestors had chimplike hands that evolved over time. "The findings suggest that the structure of the modern human hand is largely primitive in nature, rather than, as some believe, the result of more recent changes necessary for stone tool-making," a university rep tells Discovery News. Almécija adds the human changes that allowed for toolmaking likely occurred in the brain. So why were our ancestors capable of precision grasping if not to snatch up tools? Almécija suggests the adaptation made them better at gathering foods. Humans apparently weren’t the only ones to have that skill. The study suggests capuchins, baboons, and gorillas, developed a strong grip at the same time. (Another researcher claims our hands evolved for punching.)