Observed and expected variation in hominid evolution

All of the major groups of fossil hominids (australopithecines, pithecanthropines, Neandertals, and early sapiens) were discovered by 1925, and therefore prior to the formulation of the synthetic theory of evolution that revolutionized the concept of the species in systematics. While these fossil finds were being made the framework for their interpretation included several assumptions: (1) that the number of living hominoid species was great, and that intraspecific variation was slight (authoritative sources recognized as many as 14 separate species of chimpanzees and 15 species of gorillas); (2) that the timescale of human evolution was brief (measured in tens or hundreds of thousands of years). As a result of these premises the consensus that hominid evolution was characterized by a large number of sympatric and synchronic species was virtually inevitable.In contrast, recent molecular studies demonstrate that genetic diversity among recent hominoids is so slight that even humans and chimpanzees differ at only about 1% of the loci that have been sampled so far; evidently, very small genetic differences can produce rather great contrasts in morphology. At the same time, geological break-throughs have increased the timescale for human evolution to several million years.It is concluded that morphological differences among fossil hominids, even if very appreciable and complex, do not necessarily reflect a great degree of either genetic or taxonomic diversity. Potential effects of evolutionary change through time should be incorporated into models of hominid evolution as a means of assessing the minimum number of lineages required to account for observed variations among hominid specimens.     

PERSPECTIVE: EVOLUTIONARY PATTERNS IN THE FOSSIL RECORD

The study of large-scale evolutionary patterns in the fossil record has benefited from a diversity of approaches, including analysis of taxonomic data, ecology, geography, and morphology. Although genealogy is an important component of macroevolution, recent visions of phylogenetic analysis as replacing rather than supplementing other approaches are short-sighted. The ability of traditional Linnaean taxa to document evolutionary patterns is mainly an empirical rather than a theoretical issue, yet the use of these taxa has been dismissed without thorough evaluation of their empirical properties. Phylogenetic analysis can help compensate for some of the fossil record's imperfections. However, the shortcomings of the phylogenetic approach have not been adequately acknowledged, and we still lack a rigorous comparison between the phylogenetic approach and probabilistic approaches based on sampling theory. Important inferences about the history of life based on nongenealogical data have later been corroborated with genealogical and other analyses, suggesting that we risk an enormous loss of knowledge and understanding if we categorically dismiss nonphylogenetic data.     

Delimitating cryptic species in the Gracilaria domingensis complex (Gracilariaceae,Rhodophyta) using molecular and morphological data

Species in the genus Gracilaria that display conspicuously flattened vegetative morphologies are a taxonomically challenging group of marine benthic red algae. This is a result of their species richness, morphological similarity, and broad phenotypic plasticity. Within this group, the Gracilaria domingensis complex is one of the most common, conspicuous, and morphologically variable species along the tropical western Atlantic Ocean. Previous research has identified that members of this complex belong to two distantly related clades. However, despite this increased phylogentic resolution, species delimitations within each of these clades remain unclear. Our study assessed the species diversity within this difficult complex using morphological and molecular data from three genetic markers (cox1, UPA, and rbcL). We additionally applied six single‐marker species delimitation methods (SDM: ABGD, GMYCs, GMYCm, SPN, bPTP, and PTP) to rbcL, which were largely in agreement regarding species delimitation. These results, combined with our analysis of morphology, indicate that the G. domingensis complex includes seven distinct species, each of which are not all most closely related: G. cervicornis; a ressurected G. ferox; G. apiculata subsp. apiculata; a new species, Gracilaria baiana sp. nov.; G. intermedia subsp. intermedia; G. venezuelensis; and G. domingensis sensu stricto, which includes the later heterotypic synonym, G. yoneshigueana. Our study demonstrates the value of multipronged strategies, including the use of both molecular and morphological approaches, to decipher cryptic species of red algae.     

The tree, the network, and the species

To enrich the Hennigian internodal conception of species, a new formalization of the definition of the species concept is proposed. This rigorous definition allows for considerable unification of the various, and sometimes conflicting, techniques of species delimitation used in practice. First, the domain of such a definition is set out, namely, the set of all organisms on Earth, past, present, and future. Next, the focus is on the genealogical relationship among organisms, which provides the key to analysing the giant or global genealogical network (GGN) connecting all these organisms. This leads to the construction of an algorithm revealing the topological structure of the GGN, from families to lineages, ending up with a definition of species as equivalence classes of organisms corresponding to branches of the 'tree of life'. Such a theoretical definition of the species concept must be accompanied by various recognition criteria to be operational. These criteria are, for example, the ill-named 'biological species concepts', 'phylogenetic species concepts', etc., usually, but wrongly, presented as definitions of the species concept. Besides clarifying this disputed point, the definition in the present study displays the huge diversity of the scales (time-scale and population size) involved in actual species, thus explaining away the classical problems raised by previous attempts at defining the species concept (uniparental reproduction, temporal depth of species, and hybridization).  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 509–521.     

Electron spin resonance dating in paleoanthropology

Many archeological and paleoanthropological sites cannot be dated by well established and common dating techniques such as uranium series (U-series) or argon-argon (⁴⁰Ar/³⁹Ar) because of the lack of materials that are suitable for these techniques. Most sites, however, contain bones and teeth, and the latter can be used to obtain electron spin resonance (ESR) age estimates. The theoretical age range of ESR dating accuracy lies between a few thousand and more than a million years. In practice, continuing uranium accumulation increases the uncertainty of ESR age assessments in such a way that most age assignments beyond 300,000 years are very uncertain.     

How species longevity, intraspecific morphological variation, and geographic range size are related: a comparison using late Cambrian trilobites

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but it is also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall.     

The meaning of Hominidae

Traditional taxonomy of Hominoidea collides head on with the latest proposals of classification, grounded on molecular studies. Therefore, the common-sense meaning of “hominidae” does not fit some of the current technical meaning anymore. Besides, there is no consensus among molecular scholars about what genera should be placed into the Hominidae family. Some possible solution to this problem are examined in this article. It is eventually proposed a tentative classification of humans and great apes that, keeping the traditional Hominidae family (Simpson), might be accepted from the point of view of cladistic and molecular studies.     

Fish species – how and why

It is argued, with selected examples from freshwaterfish systematics, that species should be viewed as anexpression of self-perpetuated clustered variation innature, conforming to the phylogenetic speciesconcept. The importance of species lies in thefunctional and structural significance of theirdiagnostic characters. Species can be nested by theircharacters into a tree diagram (phylogeny) orhierarchical alignment structure (classification) ofcharacter distribution, which may be taken to reflectevolution, the unifying theory of organismaldiversification. The phylogenetic species concept,which emphasizes recognition of a pattern ofvariation, describes better than any other proposedconcept the units called species by systematists.Other concepts are based on processes and normally donot permit recognition of particular taxa. Specieshave unique histories, and speciation may proceed bydifferent mechanisms. Whereas it may be postulatedthat speciation entails an irreversible change in thegenetic structure of taxa, recognized by phenotypicexpression and apparently also maintained to a largeextent by selection for a particular phenotype,species recognition must remain independent ofassumptions about species history and spatialdistribution. Species are monophyletic taxa and thespecies category does not differ significantly inphylogenetic regard from other systematic categories.Species as such are not necessarily evolutionaryunits. It is recommended to apply species names withreference to the diagnostic characters of the speciesand to abandon the type specimen described by theInternational Code of Zoological Nomenclature as anomenclatural reference unit.     

Can revisionism,in evolutionary biology,help in formulating hypotheses about hominid evolution?

While evolutionary theory has been undergoing considerable revision for more than a decade scarcely any biological scientists are willing to resurrect the notion of acquired inheritance since it totally jndermines the concept of ancestor-descendant stability. Acquired inheritance is divisible into two components, soma to germ transfer to replicable information and directed or anticipatory mutation. Pure soma to germ transfer still allows for random events or natural selection as is evident from E. Steel’s proposal of the “somatic selection hypothesis”. Directed mutation is non-stochastic and self-referent. Recent bacterial research has claimed strong support for directed mutation but this phenomenon still would not be important for the small proportion of living taxa (including primates) who sequester their germlines early in ontogeny. There is a basic incompatibility between purposeful responses to final growth stages in complex metazoans and the need to permanently fix future growth into heritable programs. Symposium on Foundations for different approaches to the study of human evolution September 1–3, 1989, Liblice, Czechoslovakia, Czechoslovak Academy of Science     

Hominid cranial remains from upper Pleistocene deposits at Aduma, Middle Awash, Ethiopia

The Upper Pleistocene localities of Aduma and Bouri have yielded hominid fossils and extensive Middle Stone Age (MSA) archaeological assemblages. The vertebrate fossils recovered include parts of four hominid crania from Aduma and a complete right parietal from Bouri. Archaeological associations and radiometric techniques suggest an Upper Pleistocene age for these hominids. The more complete cranium from Aduma (ADU-VP-1/3) comprises most of the parietals, the occipital, and part of the frontal. This cranium is compared to late Middle and Upper Pleistocene hominid crania from Africa and the Middle East. The Aduma cranium shows a mosaic of cranial features shared with "premodern" and anatomically modern Homo sapiens. However, the posterior and lateral cranial dimensions, and most of its anatomy, are centered among modern humans and resemble specimens from Omo, Skhul, and Qafzeh. As a result, the Aduma and Bouri Upper Pleistocene hominids are assigned to anatomically modern Homo sapiens.     

New species of Hispanomys (Rodentia,Cricetodontinae) from the Upper Miocene of Batallones (Madrid,Spain)

Material of Hispanomys (Rodentia, Cricetodontinae) is described from various localities at Batallones (MN10) (Madrid, Spain). All of it belongs to a single species, which differs from the other known species of the genus and a new taxon, Hispanomys moralesi sp. nov. , is created for it. The samples from the various localities show differences interpreted as being the result of slight age disparities amongst the different sites. Although they were previously thought to be coeval, Batallones 10 is probably older than Batallones 1, which is possibly older than Batallones 3. Hispanomys moralesi sp. nov. is characterized by several morphological features such as the lack of cingula and mesolophs, the presence of well‐developed ectolophs, four‐ or five‐rooted M1, short or absent mesolophids, and reduced and simplified M3. Hispanomys moralesi sp. nov. is a relatively derived species, the evolutionary stage of which is comparable to those of other members of the genus from the Upper Vallesian. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 725–747.     

Morphology and function of the lumbar spine of the Kebara 2 Neandertal

The morphology of the lumbar spine is crucial for upright posture and bipedal walking in hominids. The excellent preservation of the lumbar spine of Kebara 2 provides us a rare opportunity to observe a complete spine and explore its functionally relevant morphology. The lumbar spine of Kebara 2 is analyzed and compared with the lumbar spines of modern humans and late Pleistocene hominids. Although no size differences between the vertebral bodies and pedicles of Kebara 2 and modern humans are found, significant differences in the size and orientation of the transverse processes (L₁‐L₄), and the laminae (L₅, S₁) are demonstrated. The similarity in the size of the vertebral bodies and pedicles of Kebara 2 and modern humans suggests similarity in axial load transmission along the lumbar spine. The laterally projected (L₂‐L₄) and the cranially oriented (L₁, L₃) transverse processes of Kebara 2 show an advantage for lateral flexion of the lumbar spine compared with modern humans. The characteristic morphology of the lumbar spine of Kebara 2 might be related to the wide span of its pelvic bones. Am J Phys Anthropol 142:549–557, 2010. © 2010 Wiley‐Liss, Inc.     

The evolution of brain size and intelligence in man

The brain size of hominids has increased approximately threefold during the evolution of the hominids fromAustralopithecus toHomo sapiens. It is proposed that the principal reason for this increase is that larger brains conferred greater intelligence, and greater intelligence conferred a selection advantage. A number of anthropologists have difficulty accepting this thesis because they believe that brain size is not associated with intelligence in man. Evidence is reviewed, and new evidence from two studies is presented, to show that brain size as measured by head size is positively correlated with intelligence as measured by intelligence tests. On two recent samples statistically significant correlations of .21 and .30 were obtained between estimates of brain size and IQ. It is considered that brain size is positively associated with intelligence in man and that this is the major reason for the increase in brain size of the hominids during the last 3.2 million years.     

Mio-Pliocene mammals from the Middle Awash, Ethiopia

The Middle Awash paleontological study area, located in the Afar Rift of Ethiopia, has yielded fossils spanning the last six million years. The geology and geochronology of the Mio-Pliocene sites of the study area have been refined and a reliable chronostratigraphy has been established by ⁴⁰Ar/³⁹Ar radiometric dating. The latest Miocene Adu-Asa Formation is divided into four members distinguished from each other by silicic and basaltic tuff marker horizons, most of which are dated basaltic tuffs. Radiometric dating has constrained the age of the Adu-Asa Formation to between 5.2-5.8 Ma. These dates are also supported by paleomagnetic results and biochronology. More than 2,000 fossil specimens were collected from the Adu-Asa Formation between 1992 and 2000. These fossils document 64 mammalian species belonging to 32 genera, 23 families, and 8 orders. This assemblage includes a number of new taxa. Included in the assemblage are First and Last Appearance Datums (FADs and LADs) of some groups, including the earliest record of the hominid genus Ardipithecus. Most of the taxa indicate a predominance of mesic and wooded habitat during the deposition of the Adu-Asa Formation. In these deposits, colobines, viverrids, mustelids, bovines, boselaphines, and tragelaphines are abundant, whereas alcelaphines are absent. Quantitative analyses of biogeographic relationships of the Middle Awash Late Miocene (MALM) mammalian fauna indicate stronger relationships with other African sites than with faunas from Eurasian sites. The MALM deposits have generated a critical dataset for analytic work on past environments, biogeographic relationships, and African vertebrate evolution. Moreover, the geographic position of the Middle Awash, coupled with its precise calibration and chronological span, make it a key section for interpreting latest Miocene faunal interchanges between Africa and Eurasia.     

Comparative cytogenetic analysis of eleven species of subfamilies Neoplecostominae and Hypostominae (Siluriformes: Loricariidae)

The family Loricariidae with about 690 species divided into six subfamilies, is one of the world’s largest fish families. Recent studies have shown the existence of several problems in the definition of natural groups in the family, which has made the characterization of the subfamilies and even of some genera quite difficult. With the main objective of contributing for a better understanding of the relationships between loricariids, cytogenetic analysis were conducted with two species of Neoplecostominae and nine species of Hypostominae that, according to morphological and molecular data, may belong to a new monophyletic unit. The results obtained showed a marked chromosomal conservation with the presence of 2n = 54 chromosomes and single interstitial Ag-NORs in all species analyzed. Considering that Neoplecostominae is the primitive sister-group of all other loricariids, with exception of Lithogeneinae, this karyotypic structure may represent the primitive condition for the family Loricariidae. The cytogenetic characteristics partaken by the species of Neoplecostominae and Hypostominae analyzed in the present study reinforce the hypothesis that the species of both these subfamilies might belong to a natural group.     

Chromosome numbers in Brazilian species of Crotalaria (Leguminosae, Papilionoideae) and their taxonomic significance

Chromosome numbers were counted for 23 species of Crotalaria native to Brazil. Among these data there were new counts for 15 taxa, and some confirmed previous reports or represented numbers that were different from those cited previously. The chromosome numbers most frequently found were 2 n  = 16 and 2 n  = 32. Only C. incana L. had 2 n  = 14 and C. tweediana Benth. had 2 n  = 54. The counts 2 n  = 32 and 54 were found in species of section Calycinae and 2 n  = 16 and 14 in species of section Chrysocalycinae . The data revealed the importance of chromosomal parameters in the characterization of sections Calycinae and Chrysocalycinae in Brazil. We discuss the systematic significance and evolutionary aspects for the genus, comparing the results with the two sections that are native in Brazil.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 271–277.     

Evidence for parallel ecological speciation in scincid lizards of the Eumeces skiltonianus species group (Squamata: Scincidae)

We identify instances of parallel morphological evolution in North American scincid lizards of the Eumeces skiltonianus species group and provide evidence that this system is consistent with a model of ecological speciation. The group consists of three putative species divided among two morphotypes, the small-bodied and striped E. skiltonianus and E. lagunensis versus the large-bodied and typically uniform-colored E. gilberti. Members of the group pass through markedly similar phenotypic stages during early development, but differ with respect to where terminal morphology occurs along the developmental sequence. The morphotypes also differ in habitat preference, with the large-bodied gilberti form generally inhabiting lower elevations and drier environments than the smaller, striped morphs. We inferred the phylogenetic relationships of 53 skiltonianus group populations using mtDNA sequence data from the ND4 protein-coding gene and three flanking tRNAs (900 bp total). Sampling encompassed nearly the entire geographic range of the group, and all currently recognized species and subspecies were included. Our results provide strong evidence for parallel origins of three clades characterized by the gilberti morphotype, two of which are nested within the more geographically widespread E. skiltonianus. Eumeces lagunensis was also nested among populations of E. skiltonianus. Comparative analyses using independent contrasts show that evolutionary changes in body size are correlated with differences in adult color pattern. The independently derived association of gilberti morphology with warm, arid environments suggests that phenotypic divergence is the result of adaptation to contrasting selection regimes. We provide evidence that body size was likely the target of natural selection, and that divergences in color pattern and mate recognition are probable secondary consequences of evolving large body size.     

Head size,weaponry, and cervical adaptation: Testing craniocervical evolutionary hypotheses in Ceratopsia

The anterior cervical vertebrae form the skeletal connection between the cranial and postcranial skeletons in higher tetrapods. As a result, the morphology of the atlas‐axis complex is likely to be shaped by selection pressures acting on either the head or neck. The neoceratopsian (Reptilia:Dinosauria) syncervical represents one of the most highly modified atlas‐axis regions in vertebrates, being formed by the complete coalescence of the three most anterior cervical vertebrae. In ceratopsids, the syncervical has been hypothesized to be an adaptation to support a massive skull, or to act as a buttress during intraspecific head‐to‐head combat. Here, we test these functional/adaptive hypotheses within a phylogenetic framework and critically examine the previously proposed methods for quantifying relative head size in the fossil record for the first time. Results indicate that neither the evolution of cranial weaponry nor large head size correlates with the origin of cervical fusion in ceratopsians, and we, therefore, reject both adaptive hypotheses for the origin of the syncervical. Anterior cervical fusion has evolved independently in a number of amniote clades, and further research on extant groups with this peculiar anatomy is needed to understand the evolutionary basis for cervical fusion in Neoceratopsia.