Aping our ancestors: Comparative aspects of reproductive ecology

There are many similarities among mammalian species in how ecological factors affect their reproductive potential and individual life histories. One of the most important limiting factors is the availability of sufficient resources to partition among essential growth, maintenance, and eventual reproduction.^1–3 How each mammal juggles these constraints constitutes its unique life history and determines its success as a species. Yet, as Hill and Hurtado⁴ recently argued, life-history analyses are rarely applied to human reproduction. In fact, despite the demonstrated significance of adequate nutrition for reproductive performance among most mammalian species that have been studied,^1,3,5 many demographers, and even some biological anthropologists, have resisted the idea that humans, except under extreme famine conditions, might be subject to the same kinds of nutritional constraints that affect other mammals.^6–9.     

Devonian ancestors ofNautilus

A Famennian nautilid is described that partially fills the morphologic and stratigraphie gap between Givetian and Tournaisian records of the order. A new generic nameDasbergoceras gen. nov. is proposed for it. Its loosely coiled, slender juvenile shell indicates close relationships to earlier Lechritrochoceratidae, rather than the Oncoceratida. The shell ornamentation, with oblique ribs and longitudinal striation, appears to be the primitive feature of the order. Tight coiling of the adult shell progressively developed during the Early Carboniferous while tightly coiled embryonic shells seem to be a post-Permian feature. The septal morphology, which is the most important feature distinguishing RecentNautilus from all the Tertiary nautilids, may be inherited from Cretaceous ancestors of theCimomia Aturia lineage. The nautilids probably originated from the kionoceratid Orthoceratida in late Early Ordovician.     

The recognition of ancestors

The recognition of ancestors is problematic using cladistic logic alone because monophyletic groups (clades) are defined by shared derived characters (synapomorphies) which their ancestors must have lacked. Nevertheless, ancestors possess three key attributes. They belong within a larger, paraphyletic group. They will be morphologically most similar to their immediate descendants, and they evolved before any and all of their descendants. Recognition of ancestors requires both morphological and stratigraphic data and, in practice, the task is to reduce the size of the paraphyletic group within which the ancestor must lie. All ancestor‐descendant relationships are phylogenetic hypotheses. Despite the legendary incompleteness of the fossil record, testing the validity of available data is far more difficult for character analysis than for stratigraphy.     

Microsaurs as possible apodan ancestors

The specific ancestry and nature of the relationships of modern amphibians have not yet been established. Detailed comparisons of the anatomy of the skull roof, palate and braincase of living apodans and the Paleozoic microsaur Goniorhynchus demonstrate greater similarities than between apodans and any other group of amphibians, fossil or recent. Unlike any other amphibians, extensive pleurosphenoid ossifications are developed in the area of the Vth nerve, uniting the otic capsule with the sphenethmoid. Other important features that they share (although not uniquely) include the presence of all the primitive dermal elements of the palate, a solidly roofed temporal region, a row of palatal teeth parallel to the marginal dentition and a row of teeth on the medial surface of the lower jaw. The stapes has a similar configuration and position, totally different from that of frogs and salamanders. Such similarities do not necessarily prove close relationship, but indicate the necessity for considering that apodans may have an ancestry distinct from that of frogs and salamanders.     

Permian ancestors of Hymenoptera and Raphidioptera

The origin of Hymenoptera remains controversial. Currently accepted hypotheses consider Hymenoptera as the first side branch of Holometabola or sister-group to Mecopteroidea. In contrast, fossils confirm the idea of Martynov that Hymenoptera are related to Megaloptera and Raphidioptera. Hymenoptera have descended along with Raphidioptera from the earliest Megaloptera, the Permian Parasialidae. A related new family, minute Nanosialidae from the Permian of Russia is supposedly ancestral to Raphidioptera. The fusion of the third ovipositor valvulae is shown to be not a synapomorphy of Neuropteroidea. Parasialids and nanosialids bridge the gap between megalopterans and snakeflies; all can be classified into a single order, Panmegaloptera nom. n., including a new suborder Siarapha for Nanosialidae. The earliest megalopterans and their descendants, Raphidioptera and Hymenoptera, have passed through a “miniaturization bottleneck”, likely a common macroevolutionary mechanism.     

Phenogenetics of offspring and their ancestors

By the help of questionnaire of young peoples (18-25 years) was received an information about their psycobiological likeness to mother, father, grandmother, grandfather. From 788 girls likeness to mother marked in 50.51%, father--37.06%, grandmother--9.77%, grandfather--2.66%. Boys (416 answers) marked likeness in 34.13% with mother, in 52.64% with father, in 3.85% with grandmother, in 9.38% with grandfather. So, the girls more frequent showed there likeness to ancestors of women sex, and boys--to men sex. Authors thinking, that this thing is conditioned not only by heredity cytoplasmatic factors, but by alternative action of womanish and masculine sexual hormones.     

Species concepts and the recognition of ancestors

Whether or not ancestral species can be recognised depends on the species concept adopted. A “metaspecies”; is a species that completely lacks autapomorphies, and which might (or might not) be ancestral to other species. Such taxa have been identified among both living and fossil organisms. Under the most commonly‐used species concepts (biological, evolutionary, phenetic, phylogenetic, ecological, recognition and cohesion), “metaspecies”; can be assumed to be ancestral. Even if the known members of a metaspecies are not ancestral to anything, parsimony dictates that the (as yet unknown) ancestral lineage is identical to the metaspecies and, under these species concepts, assignable to the same species. Only the cladistic and monophyletic species concepts would deny “metaspecies”; ancestral status, but these species concepts are problematical and have never been used by practising systematists.     

Backward simulation of ancestors of sampled individuals

If the population is large and the sampling mechanism is random, the coalescent is commonly used to model the haplotypes in the sample. Ordered genotypes can then be formed by random matching of the derived haplotypes. However, this approach is not realistic when (1) there is departure from random mating (e.g., dominant individuals in breeding populations or monogamy in humans), or (2) the population is small and/or the individuals in the sample are ascertained by applying some particular non-random sampling scheme, as is usually the case when considering the statistical modeling and analysis of pedigree data. For such situations, we present here a data generation method where an ancestral graph with non-overlapping generations is first generated backwards in time, using ideas from coalescent theory. Alleles are randomly assigned to the founders, and subsequently the gene flow over the entire genome is simulated forwards in time by dropping alleles down the graph according to recombination model without interference. The parameters controlling the mating behavior of generated individuals in the graph (degree of monogamy) can be tuned in order to match a particular demographic situation, without restriction to simple random mating.The performance of the approach is illustrated with a simulation example. The software (written in C-language) is freely available for research purposes at http://www.rni.helsinki.fi/∼dag/.     

Sex‐biased dispersal of human ancestors

Some anthropologists and primatologists have argued that, judging by extant chimpanzees and humans, which are female‐biased dispersers, the common ancestors of humans and chimpanzees were also female‐biased dispersers. It has been thought that sex‐biased dispersal patterns have been genetically transmitted for millions of years. However, this character has changed many times with changes in environment and life‐form during human evolution and historical times. I examined life‐form and social organization of nonhuman primates, among them gatherers (foragers), hunter‐gatherers, agriculturalists, industrialists, and modern and extant humans. I conclude that dispersal patterns changed in response to environmental conditions during primate and human evolution.