Birth of 'human-specific' genes during primate evolution

Humans and other Anthropoids share very similar chromosome structure and genomic sequence as seen in the 98.5% homology at the DNA level between us and Great Apes. However, anatomical and behavioral traits distinguish Homo sapiens from his closest relatives. I review here several recent studies that address the issue by using different approaches: large-scale sequence comparison (first release) between human and chimpanzee, characterization of recent segmental duplications in the human genome and analysis of exemplary gene families. As a major breakthrough in the field, the heretical concept of human-specific genes has recently received some supporting data. In addition, specific chromosomal regions have been mapped that display all the features of gene nurseries and could have played a major role in gene innovation and speciation during primate evolution. A model is proposed that integrates all known molecular mechanisms that can create new genes in the human lineage.     

The Fayum primate forest: Did it exist?

The primates have the reputation of being essentially arboreal, forest-adapted animals. Yet there are many genera and species that inhabit an extremely wide array of non-forest habitats. Nevertheless, palaeoprimatologists often tend to depict fossil primate habitats as being more arboreal and more forest-like than is justified by the facts. It is worthwhile, therefore, to reconsider some current interpretations. In this paper, evidence of the Fayum Oligocene primate deposits are reviewed and discussed. The following conclusions emerge:(1) The large number of primate species indicates that the Fayum ecosystem was an optimum or near-optimum habitat for primates. (2) The lithological characteristics point to a sahélien type of climate. (3) The calcified and silicified root systems, having diameters up to 4 cm, suggest a sahélien type of shrub, bushland and/or small-tree vegetation. (4) The large fossilized logs cannot have grown on the spot and apparently represent driftwood from a more humid climatic belt in the south, as is indicated by damage resulting from fluvial transportation and by palaeobotanical data. (5) There may have been some minor patches or strips of medium-height forests and/or wood-lands in the Fayum delta, but there is no evidence of these.Thus the tall forest in which the earliest known African primates are currently supposed to have lived probably never existed. Grounds for this conclusion were presented by Unger 121 years ago, by Beadnell 75 years ago and by Kräusel 41 years ago, but sank into oblivion. The classic image of the primates as arboreal specialists seems to have interfered with seeing the facts. However, more extensive verification of the evidence by means of palaeobotanical research is still required. The fossil material to do so is readily available.     

Substrate Size and Primate Forelimb Mechanics: Implications for Understanding the Evolution of Primate Locomotion

International Journal of Primatology - Did the anatomical and locomotor specializations of primates evolve in response to requirements of locomotion and foraging on thin branches? Laboratory...     

New views on primate origins

Most primates live in trees, and many of them have strikingly human-like hands and faces. Scientists who study primate evolution agree that these two facts must be connected in some way. The details, however, are a matter of debate. Early theories explained the human-like peculiarities of primates simply as arboreal adaptations. More recent accounts have traced the origins of these peculiarities to more specific ways of arboreal life, involving leaping locomotion, shrub-layer foraging, visually guided predation on insects, or fruit-eating.     

Evolution of nocturnality in bats: Potential competitors and predators during their early history

Despite their taxonomic and ecological diversity, modern bats (Order Chiroptera) are almost exclusively nocturnal. This behaviour is too ubiquitous to be explained by common patterns of temporal variation in availability of their diverse food sources or by the risk of hyperthermia when flying during the day. Other explanations for bat nocturnality include competition and increased predation risk from birds during the day. In the early and mid Eocene, the known bat fauna consisted of several insectivorous species of sizes similar to those of the modern European assemblage. This fauna was contemporaneous with several species of predatory birds, including owls (Strigiformes), hawks (Accipitridae), falcons (Falconidae) and rollers (Coraciiformes), which were the same size as modern predators on bats. Predation risk could therefore have been a significant factor preventing the early bats from becoming diurnal. Competition from aerial insectivorous birds, however, was less likely to have been significant for bats during the early Eocene, since very few such groups, mainly small Aegialornithidae, were present, with most of the major groups of aerial insectivores evolving later.     

Baculum length and copulatory behavior in primates

The length of the baculum (os penis) was measured in 74 adult males representing 46 primate species. These data, and a review of previously published measurements, indicate that variation in baculum length among primates is related to taxonomic and behavioral differences. Thus, many New World monkeys have shorter bacula, relative to body weight, than Old World monkeys. The baculum is shorter in colobine monkeys than in cercopithecines. Among the great apes, reduction of the baculum is more pronounced in Pan and Gorilla than in Pongo. Very long bacula are found in some nocturnal prosimians (eg, Lorisidae) and also in Macaca arctoides. A comparison of baculum length relative to body weight was made in 34 species for which detailed information on copulatory behavi or was available. The presence of an elongated baculum was shown to correlate with copulatory patterns involving prolonged intromission and/or the maintenance of intromission during the postejaculatory interval (eg, Galago crassicaudatus, Loris tardigradus, M, arctoides). The evolutionary significance of these observations is discussed and it is suggeted that similar copulatory patterns may occur in species with elongated bacula (eg, Daubentonia, Perodicticus) for which behavioral data are lacking at present. The same hypothesis also applies to an extinct adapid primate which possessed a very large baculum.     

Evolution of beta satellite DNA sequences: evidence for duplication-mediated repeat amplification and spreading

In this article, we report studies on the evolutionary history of beta satellite repeats (BSR) in primates. In the orangutan genome, the bulk of BSR sequences was found organized as very short stretches of approximately 100 to 170 bp, embedded in a 60-kb to 80-kb duplicated DNA segment. The estimated copy number of the duplicon that carries BSR sequences ranges from 70 to 100 per orangutan haploid genome. In both macaque and gibbon, the duplicon mapped to a single chromosomal region at the boundary of the rDNA on the marker chromosome (chromosome 13 and 12, respectively). However, only in the gibbon, the duplicon comprised 100 bp of beta satellite. Thus, the ancestral copy of the duplicon appeared in Old World monkeys ( approximately 25 to approximately 35 MYA), whereas the prototype of beta satellite repeats took place in a gibbon ancestor, after apes/Old World monkeys divergence ( approximately 25 MYA). Subsequently, a burst in spreading of the duplicon that carries the beta satellite was observed in the orangutan, after lesser apes divergence from the great apes-humans lineage ( approximately 18 MYA). The analysis of the orangutan genome also indicated the existence of two variants of the duplication that differ for the length (100 or 170 bp) of beta satellite repeats. The latter organization was probably generated by nonhomologous recombination between two 100-bp repeated regions, and it likely led to the duplication of the single Sau3A site present in the 100-bp variant, which generated the prototype of Sau3A 68-bp beta satellite tandem organization. The two variants of the duplication, although with a different ratios, characterize the hominoid genomes from the orangutan to humans, preferentially involving acrocentric chromosomes. At variance to alpha satellite, which appeared before the divergence of New World and Old World monkeys, the beta satellite evolutionary history began in apes ancestor, where we have first documented a low-copy, nonduplicated BSR sequence. The first step of BSR amplification and spreading occurred, most likely, because the BSR was part of a large duplicon, which underwent a burst dispersal in great apes' ancestor after the lesser apes' branching. Then, after orangutan divergence, BSR acquired the clustered structural organization typical of satellite DNA.