'Chumanzee' evolution: the urge to diverge and merge

Locational diversity of alpha satellite DNA and intergeneric hybridization aspects in the Nomascus and Hylobates genera of small apes

Recently, we discovered that alpha satellite DNA has unique and genus-specific localizations on the chromosomes of small apes. This study describes the details of alpha satellite localization in the genera Nomascus and Hylobates and explores their usefulness in distinguishing parental genome sets in hybrids between these genera. Fluorescence in situ hybridization was used to establish diagnostic criteria of alpha satellite DNA markers in discriminating small ape genomes. In particular we established the genus specificity of alpha satellite distribution in three species of light-cheeked gibbons (Nomascus leucogenys, N. siki, and N. gabriellae) in comparison to that of Hylobates lar. Then we determined the localization of alpha satellite DNA in a hybrid individual which resulted from a cross between these two genera. In Nomascus the alpha satellite DNA blocks were located at the centromere, telomere, and four interstitial regions. In Hylobates detectable amounts of alpha satellite DNA were seen only at centromeric regions. The differences in alpha satellite DNA locations between Nomascus and Hylobates allowed us to easily distinguish the parental chromosomal sets in the genome of intergeneric hybrid individuals found in Thai and Japanese zoos. Our study illustrates how molecular cytogenetic markers can serve as diagnostic tools to identify the origin of individuals. These molecular tools can aid zoos, captive breeding programs and conservation efforts in managing small apes species. Discovering more information on alpha satellite distribution is also an opportunity to examine phylogenetic and evolutionary questions that are still controversial in small apes.

Archaic human genomics

For much of the 20th century, the predominant view of human evolutionary history was derived from the fossil record. Homo erectus was seen arising in Africa from an earlier member of the genus and then spreading throughout the Old World and into the Oceania. A regional continuity model of anagenetic change from H. erectus via various intermediate archaic species into the modern humans in each of the regions inhabited by H. erectus was labeled the multiregional model of human evolution (MRE). A contrasting model positing a single origin, in Africa, of anatomically modern H. sapiens with some populations later migrating out of Africa and replacing the local archaic populations throughout the world with complete replacement became known as the recent African origin (RAO) model. Proponents of both models used different interpretations of the fossil record to bolster their views for decades. In the 1980s, molecular genetic techniques began providing evidence from modern human variation that allowed not only the different models of modern human origins to be tested but also the exploration demographic history and the types of selection that different regions of the genome and even specific traits had undergone. The majority of researchers interpreted these data as strongly supporting the RAO model, especially analyses of mitochondrial DNA (mtDNA). Extrapolating backward from modern patterns of variation and using various calibration points and substitution rates, a consensus arose that saw modern humans evolving from an African population around 200,000 years ago. Much later, around 50,000 years ago, a subset of this population migrated out of Africa replacing Neanderthals in Europe and western Asia as well as archaics in eastern Asia and Oceania. mtDNA sequences from more than two-dozen Neanderthals and early modern humans re-enforced this consensus. In 2010, however, the complete draft genomes of Neanderthals and of heretofore unknown hominins from Siberia, called Denisovans, demonstrated gene flow between these archaic human species and modern Eurasians but not sub-Saharan Africans. Although the levels of gene flow may be very limited, this unexpected finding does not fit well with either the RAO model or MRE model. More thorough sampling of modern human diversity, additional fossil discoveries, and the sequencing of additional hominin fossils are necessary to throw light onto our origins and our history.

Reconstructing phylogenies and phenotypes: a molecular view of human evolution

This review broadly summarizes how molecular biology has contributed to our understanding of human evolution. Molecular anthropology began in the 1960s with immunological comparisons indicating that African apes and humans were closely related and, indeed, shared a common ancestor as recently as 5 million years ago. Although initially dismissed, this finding has proven robust and numerous lines of molecular evidence now firmly place the human-ape divergence at 4-8 Ma. Resolving the trichotomy among humans, chimpanzees and gorillas took a few more decades. Despite the readily apparent physical similarities shared by African apes to the exclusion of modern humans (body hair, knuckle-walking, thin tooth enamel), the molecular support for a human-chimpanzee clade is now overwhelming. More recently, whole genome sequencing and gene mapping have shifted the focus of molecular anthropology from phylogenetic analyses to phenotypic reconstruction and functional genomics. We are starting to identify the genetic basis of the morphological, physiological and behavioural traits that distinguish modern humans from apes and apes from other primates. Most notably, recent comparative genomic analyses strongly indicate that the marked differences between modern humans and chimpanzees are likely due more to changes in gene regulation than to modifications of the genes themselves, an idea first proposed over 30 years ago. Almost weekly, press releases describe newly identified genes and regulatory elements that seem to have undergone strong positive selection along the human lineage. Loci involved in speech (e.g. FOXP2), brain development (e.g. ASPM), and skull musculature (e.g. MYH16) have been of particular interest, but some surprising candidate loci (e.g. those involved in auditory capabilities) have emerged as well. Exciting new research avenues, such as the Neanderthal Genome Project, promise that molecular analyses will continue to provide novel insights about our evolution. Ultimately, however, these molecular findings can only be understood in light of data from field sites, morphology labs, and museum collections. Indeed, molecular anthropology depends on these sources for calibrating molecular clocks and placing genetic data within the context of key morphological and ecological transitions in human evolution.

No evidence of a Neanderthal contribution to modern human diversity

Recent studies of genomic DNA from Neanderthal fossils support earlier studies showing no contribution of Neanderthals to the gene pool of modern humans.

The relationship between Neanderthals and modern humans is contentious, but recent advances in Neanderthal genomics have shed new light on their evolutionary history. Here we review the available evidence and find no indication of any Neanderthal contribution to modern genetic diversity.

A most distant intergeneric hybrid offspring (Larcon) of lesser apes, Nomascus leucogenys and Hylobates lar

Unlike humans, which are the sole remaining representatives of a once larger group of bipedal apes (hominins), the "lesser apes" (hylobatids) are a diverse radiation with numerous extant species. Consequently, the lesser apes can provide a valuable evolutionary window onto the possible interactions (e.g., interbreeding) of hominin lineages coexisting in the same time and place. In the present work, we employ chromosomal analyses to verify the hybrid ancestry of an individual (Larcon) produced by two of the most distant genera of lesser apes, Hylobates (lar-group gibbons) and Nomascus (concolor-group gibbons). In addition to a mixed pelage pattern, the hybrid animal carries a 48-chromosome karyotype that consists of the haploid complements of each parental species: Hylobates lar (n = 22) and Nomascus leucogenys leucogenys (n = 26). Studies of this animal's karyotype shed light onto the processes of speciation and genus-level divergence in the lesser apes and, by extension, across the Hominoidea.