Ancestral Apes Research Articles

The evolutionary origin of human kissing.

A kiss has been a signal of special affection across continents and cultures for millennia. Between times and peoples, social norms invariably prescribe kissing to specific affiliations and contexts, implying deeper biological bases. Why the protruding of the lips and slight suction when touching another? Capuchin monkeys stick their fingers in their friends' eyes as sign of affection, why have humans developed kissing? Here I briefly review proposed hypotheses for the evolution of human kissing. Great ape social behavior suggests that kissing is likely the conserved final mouth-contact stage of a grooming bout when the groomer sucks with protruded lips the fur or skin of the groomed to latch on debris or a parasite. The hygienic relevance of grooming decreased over human evolution due to fur-loss, but shorter sessions would have predictably retained a final "kissing" stage, ultimately, remaining the only vestige of a once ritualistic behavior for signaling and strengthening social and kinship ties in an ancestral ape.

The continuity of mind, from great apes to humans

​It is a central prediction from mainstream evolutionary biology that there is a continuous set of intermediate states in the mental abilities from an ape-human ancestor to modern humans. A quick analysis is given to the problem introduced by Rene Descartes of the supposed gap between mind matter and physical matter, the former distinguishing humans from all other animals. A three-pronged analysis is then given that revolves around: (1) the continuity of mind from young children to adults; (2) the similarity of measured mental abilities between young great apes and young children at similar stages of development; and (3) the observation that there appear to be no unique genes in the human genome for mental abilities (including for ‘wisdom and intelligence’). The components that are required for language are then analysed, and important precursors found in the great apes. The conclusion is that the best supported hypothesis, especially in a Bayesian framework, is for a continuum in mental states between an ancestral ape and modern humans. There are a range of predictions from this model that can, and have been, tested.

The role of thrifty genes in the origin of alcoholism: A narrative review and hypothesis.

In this narrative review, we present the hypothesis that key mutations in two genes, occurring 15 and 10million years ago (MYA), were individually and then collectively adaptive for ancestral humans during periods of starvation, but are maladaptive in modern civilization (i.e., "thrifty genes"), with the consequence that these genes not only increase our risk today for obesity, but also for alcoholism. Both mutations occurred when ancestral apes were experiencing loss of fruit availability during periods of profound climate change or environmental upheaval. The silencing of uricase (urate oxidase) activity 15MYA enhanced survival by increasing the ability for fructose present in dwindling fruit to be stored as fat, a consequence of enhanced uric acid production during fructose metabolism that stimulated lipogenesis and blocked fatty acid oxidation. Likewise, a mutation in class IV alcohol dehydrogenase ~10MYA resulted in a remarkable 40-fold increase in the capacity to oxidize ethanol (EtOH), which allowed our ancestors to ingest fallen, fermenting fruit. In turn, the EtOH ingested could activate aldose reductase that stimulates the conversion of glucose to fructose, while uric acid produced during EtOH metabolism could further enhance fructose production and metabolism. By aiding survival, these mutations would have allowed our ancestors to generate more fat, primarily from fructose, to survive changing habitats due to the Middle Miocene disruption and also during the late-Miocene aridification of East Africa. Unfortunately, the enhanced ability to metabolize and utilize EtOH may now be acting to increase our risk for alcoholism, which may be yet another consequence of once-adaptive thrifty genes.

The Complexity and Phylogenetic Continuity of Laughter and Smiles in Hominids.

Laughter and smiles are often, but not always, associated with positive affect. These expressions of humans help to promote social relationships as well as the development of cognitive and socio-emotional skills and they may have a positive impact on health and well-being, hereby covering a selection of fitness-relevant benefits. Both laughter and smiles of positive affect also occur early in human development and across cultures, suggesting deep roots in human biology. The present work provides an evolutionary reconstruction of the evolution of human laughter and smiles of positive affect in form and function, based on the principle of maximum parsimony. According to the Complexity and Continuity Hypothesis, human laughter and smiles of positive affect must have evolved within the context of play from ancestral species. Furthermore, ancestral ape laughter and their open-mouth faces must already have been complex in form and function and changed over time via categorically different phylogenetic pathways to become characteristic, effective, and pervasive behaviors of everyday social interactions in humans.

The evolution and population diversity of human-specific segmental duplications.

SUMMARYSegmental duplications contribute to human evolution, adaptation and genomic instability but are often poorly characterized. We investigate the evolution, genetic variation and coding potential of human-specific segmental duplications (HSDs). We identify 218 HSDs based on analysis of 322 deeply sequenced archaic and contemporary hominid genomes. We sequence 550 human and nonhuman primate genomic clones to reconstruct the evolution of the largest, most complex regions with protein-coding potential (n=80 genes/33 gene families). We show that HSDs are non-randomly organized, associate preferentially with ancestral ape duplications termed “core duplicons”, and evolved primarily in an interspersed inverted orientation. In addition to Homo sapiens-specific gene expansions (e.g., TCAF1/2), we highlight ten gene families (e.g., ARHGAP11B and SRGAP2C) where copy number never returns to the ancestral state, there is evidence of mRNA splicing, and no common gene-disruptive mutations are observed in the general population. Such duplicates are candidates for the evolution of human-specific adaptive traits.

Practice makes perfect: Performance optimisation in ‘arboreal’ parkour athletes illuminates the evolutionary ecology of great ape anatomy

An animal's size is central to its ecology, yet remarkably little is known about the selective pressures that drive this trait. A particularly compelling example is how ancestral apes evolved large body mass in such a physically and energetically challenging environment as the forest canopy, where weight-bearing branches and lianas are flexible, irregular and discontinuous, and the majority of preferred foods are situated on the most flexible branches at the periphery of tree crowns. To date the issue has been intractable due to a lack of relevant fossil material, the limited capacity of the fossil record to reconstruct an animal's behavioural ecology and the inability to measure energy consumption in freely moving apes. We studied the oxygen consumption of parkour athletes while they traversed an arboreal-like course as an elite model ape, to test the ecomorphological and behavioural mechanisms by which a large-bodied ape could optimize its energetic performance during tree-based locomotion. Our results show that familiarity with the arboreal-like course allowed the athletes to substantially reduce their energy expenditure. Furthermore, athletes with larger arm spans and shorter legs were particularly adept at finding energetic savings. Our results flesh out the scanty fossil record to offer evidence that long, strong arms, broad chests and a strong axial system, combined with the frequent use of uniform branch-to-branch arboreal pathways, were critical to off-setting the mechanical and energetic demands of large mass in ancestral apes.

Causal or Noncausal Relationship of Uric Acid With Diabetes.

Humans and great apes have higher serum uric acid due to mutations that reduced activity and then silenced the uricase gene about 15 million years ago (1). Uricase degrades intracellular urate in the liver, resulting in low serum uric acid. Parallel silencing of uricase occurred in lesser apes, suggesting natural selection for higher serum uric acid. Uric acid is an antioxidant in the extracellular environment, reacting with superoxide (to make allantoin) and with peroxynitrite (to make triuret). These antioxidant properties of uric acid were proposed to be beneficial by protecting against aging and cancer-associated oxidative stress (2). A different hypothesis has also been proposed (3). The uricase mutation occurred during a period of global cooling that caused seasonal famines for ancestral apes living in Europe due to loss of fruit availability during winter months. The primary food for these ancestral apes was fruit rich in fructose, a nutrient that predisposes to increased hepatic and visceral fat stores and insulin resistance due to its unique metabolism in which transient ATP depletion occurs (4). The nucleotide turnover generates urate intracellularly with a rise in serum uric acid. The intracellular urate causes mitochondrial oxidative stress and inhibits AMPK, resulting in liver fat accumulation, gluconeogenesis, and metabolic syndrome (5,6). Inhibition of uricase amplifies the effects of fructose to induce metabolic syndrome, whereas expressing the ancestral uricase in human liver …

Chimpanzees (Pan troglodytes) Produce the Same Types of 'Laugh Faces' when They Emit Laughter and when They Are Silent.

The ability to flexibly produce facial expressions and vocalizations has a strong impact on the way humans communicate, as it promotes more explicit and versatile forms of communication. Whereas facial expressions and vocalizations are unarguably closely linked in primates, the extent to which these expressions can be produced independently in nonhuman primates is unknown. The present work, thus, examined if chimpanzees produce the same types of facial expressions with and without accompanying vocalizations, as do humans. Forty-six chimpanzees (Pan troglodytes) were video-recorded during spontaneous play with conspecifics at the Chimfunshi Wildlife Orphanage. ChimpFACS was applied, a standardized coding system to measure chimpanzee facial movements, based on FACS developed for humans. Data showed that the chimpanzees produced the same 14 configurations of open-mouth faces when laugh sounds were present and when they were absent. Chimpanzees, thus, produce these facial expressions flexibly without being morphologically constrained by the accompanying vocalizations. Furthermore, the data indicated that the facial expression plus vocalization and the facial expression alone were used differently in social play, i.e., when in physical contact with the playmates and when matching the playmates’ open-mouth faces. These findings provide empirical evidence that chimpanzees produce distinctive facial expressions independently from a vocalization, and that their multimodal use affects communicative meaning, important traits for a more explicit and versatile way of communication. As it is still uncertain how human laugh faces evolved, the ChimpFACS data were also used to empirically examine the evolutionary relation between open-mouth faces with laugh sounds of chimpanzees and laugh faces of humans. The ChimpFACS results revealed that laugh faces of humans must have gradually emerged from laughing open-mouth faces of ancestral apes. This work examines the main evolutionary changes of laugh faces since the last common ancestor of chimpanzees and humans.

Embodied niche construction in the hominin lineage: semiotic structure and sustained attention in human embodied cognition.

Human evolution unfolded through a rather distinctive, dynamically constructed ecological niche. The human niche is not only generally terrestrial in habitat, while being flexibly and extensively heterotrophic in food-web connections. It is also defined by semiotically structured and structuring embodied cognitive interfaces, connecting the individual organism with the wider environment. The embodied dimensions of niche-population co-evolution have long involved semiotic system construction, which I hypothesize to be an evolutionarily primitive aspect of learning and higher-level cognitive integration and attention in the great apes and humans alike. A clearly pre-linguistic form of semiotic cognitive structuration is suggested to involve recursively learned and constructed object icons. Higher-level cognitive iconic representation of visually, auditorily, or haptically perceived extrasomatic objects would be learned and evoked through indexical connections to proprioceptive and affective somatic states. Thus, private cognitive signs would be defined, not only by their learned and perceived extrasomatic referents, but also by their associations to iconically represented somatic states. This evolutionary modification of animal associative learning is suggested to be adaptive in ecological niches occupied by long-lived, large-bodied ape species, facilitating memory construction and recall in highly varied foraging and social contexts, while sustaining selective attention during goal-directed behavioral sequences. The embodied niche construction (ENC) hypothesis of human evolution posits that in the early hominin lineage, natural selection further modified the ancestral ape semiotic adaptations, favoring the recursive structuration of concise iconic narratives of embodied interaction with the environment.

Mutational Tail Loss Is an Evolutionary Mechanism for Liberating Marapsins and Other Type I Serine Proteases from Transmembrane Anchors

Human and mouse marapsins (Prss27) are serine proteases preferentially expressed by stratified squamous epithelia. However, mouse marapsin contains a transmembrane anchor absent from the human enzyme. To gain insights into physical forms, activities, inhibition, and roles in epithelial differentiation, we traced tail loss in human marapsin to a nonsense mutation in an ancestral ape, compared substrate preferences of mouse and human marapsins with those of the epithelial peptidase prostasin, designed a selective substrate and inhibitor, and generated Prss27-null mice. Phylogenetic analysis predicts that most marapsins are transmembrane proteins. However, nonsense mutations caused membrane anchor loss in three clades: human/bonobo/chimpanzee, guinea pig/degu/tuco-tuco/mole rat, and cattle/yak. Most marapsin-related proteases, including prostasins, are type I transmembrane proteins, but the closest relatives (prosemins) are not. Soluble mouse and human marapsins are tryptic with subsite preferences distinct from those of prostasin, lack general proteinase activity, and unlike prostasins resist antiproteases, including leupeptin, aprotinin, serpins, and α2-macroglobulin, suggesting the presence of non-canonical active sites. Prss27-null mice develop normally in barrier conditions and are fertile without overt epithelial defects, indicating that marapsin does not play critical, non-redundant roles in development, reproduction, or epithelial differentiation. In conclusion, marapsins are conserved, inhibitor-resistant, tryptic peptidases. Although marapsins are type I transmembrane proteins in their typical form, they mutated independently into anchorless forms in several mammalian clades, including one involving humans. Similar pathways appear to have been traversed by prosemins and tryptases, suggesting that mutational tail loss is an important means of evolving new functions of tryptic serine proteases from transmembrane ancestors.

The scope of culture in chimpanzees, humans and ancestral apes

More studies have focused on aspects of chimpanzee behaviour and cognition relevant to the evolution of culture than on any other species except our own. Accordingly, analysis of the features shared by chimpanzees and humans is here used to infer the scope of cultural phenomena in our last common ancestor, at the same time clarifying the nature of the special characteristics that advanced further in the hominin line. To do this, culture is broken down into three major aspects: the large scale, population-level patterning of traditions; social learning mechanisms; and the behavioural and cognitive contents of culture. Each of these is further dissected into subcomponents. Shared features, as well as differences, are identified in as many as a dozen of these, offering a case study for the comparative analysis of culture across animal taxa and a deeper understanding of the roots of our own cultural capacities.

Locomotor versatility in the white-handed gibbon ( Hylobates lar): A spatiotemporal analysis of the bipedal, tripedal, and quadrupedal gaits

This study gives a qualitative and quantitative description of the different terrestrial locomotor modes of a group of white-handed gibbons ( Hylobates lar) from the Wild Animal Park Planckendael, Belgium. The gibbons were filmed during voluntary locomotion on a grassy and smooth substrate and on a pole. These video images allowed us to define seven different gait types, based on spatial and temporal footfall patterns. Consequent digitization of the video images ( n = 254) yielded duty factors, stride lengths, and stride frequencies of the fore- and hind limbs during locomotion at a wide range of speeds. These spatiotemporal gait characteristics were regressed against velocity, and the regression lines of the different gait types were compared. In addition, gibbon bipedalism was compared with bonobo ( Pan paniscus) and human bipedalism. Gibbons appear to be very versatile animals, using a bipedal, tripedal, or quadrupedal gait during terrestrial travel with an overlapping speed range. The spatiotemporal characteristics of these gaits are largely similar, although they have clearly distinct footfall patterns. Bipedal walking on the pole is slightly different from terrestrial bipedalism, but differences between substrate types (grass vs. catwalk) are subtle. During bipedalism, gibbons increase both stride length and frequency to increase speed, just as humans and bonobos do, but at a given speed, gibbons take relatively larger strides at lower rates. Bipedal walking in gibbons also appears to be relatively fast—gibbons could keep on walking at speeds where humans have to start running. Apparently, adaptations for arboreal locomotion have not constrained the terrestrial locomotor abilities of gibbons. This may indicate that the step from an arboreal ancestral ape to a terrestrial, upright bipedal hominin might not be difficult and that structural specializations are not a prerequisite for adopting a (non-habitual) bipedal gait.

Origin of human chromosome 2 revisited

Similarities in chromosome banding patterns and hornologies in DNA sequence between chromosomes of the great apes and humans have suggested that human chromosome 2 originated through the fusion of two ancestral ape chromosomes. A lot of work has been directed at understanding the nature and mechanism of this fusion. The recent availability of the human chrornosome-2-specific alpha satellite DNA probe D2Z and the human chromosome-2p-specific subtelomeric DNA probe D2S445 prompted us to attempt cross-hybridization with chromosomes of the chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla) and orangutan (Pongo pygmaeus) to search for equivalent locations in the great apes and to comment on the origin of human chromosome 2. The probes gave different results. No hybridization to the chromosome-2-specific alpha satellite DNA probe was observed on the presumed homologous great ape chromosomes using both high-stringency and low-stringency post-hybridization washes, whereas the subtelomeric-DNA probe specific for chromosome 2p hybridized to telomeric sites of the short arm of chromosome 12 of all three great apes. These observations suggest an evolutionary difference in the number of alpha satellite DNA repeat units in the equivalent ape chromosomes presumably involved in the chromosome fusion. Nevertheless, complete conservation of DNA sequence of the subtelomeric repeat sequence D2S445 in the ape chromosomes is demonstrated.

FRA2B is distinct from inverted telomere repeat arrays at 2q13

Human chromosome 2 was formed by a telomere-to-telomere fusion of two ancestral ape chromosomes. The fusion point is localized in chromosomal band 2q13, which also contains the rare, folate-sensitive fragile site FRA2B. It has been hypothesized that this fragile site may be related to the presence of interstitial telomeric and subtelomeric sequences, which have come to lie in an inverted repeat arrangement as a result of the fusion event. Fluorescence in situ hybridization of a genomic cosmid c8.1, which spans the fusion point, was carried out on metaphase spreads of an individual who expressed the fragile site at 2q13. We show that the fusion point maps distal to this fragile site. Therefore, we conclude that the inverted arrays of telomeric and subtelomeric sequences found at this fusion point are unlikely to correspond to the rare fragile site at 2q13.

Origin of human chromosome 2: an ancestral telomere-telomere fusion.

We have identified two allelic genomic cosmids from human chromosome 2, c8.1 and c29B, each containing two inverted arrays of the vertebrate telomeric repeat in a head-to-head arrangement, 5'(TTAGGG)n-(CCCTAA)m3'. Sequences flanking this telomeric repeat are characteristic of present-day human pretelomeres. BAL-31 nuclease experiments with yeast artificial chromosome clones of human telomeres and fluorescence in situ hybridization reveal that sequences flanking these inverted repeats hybridize both to band 2q13 and to different, but overlapping, subsets of human chromosome ends. We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2.