Birth Mechanisms in Australopithecus.
Emma Nelson B.Sc. Dissertation 1998
There are diverse opinions concerning the ease or difficulty of australopithecine birth. The fossil record has not been generous in helping solve this question. Despite the existence of only two fossil pelves many interpretations and reconstructions have been made. The constraints on the evolution of the pelvis, and the relevance of encephalization and allometry to neonatal head size, are examined. The literature concerning previous pelvic reconstructions, together with that on neonatal head size is reviewed, and allowances made for factors that could be significant in a live birth by reference to human and extant primate data. The graphical model is adapted to allow comparisons of estimated neonatal head sizes with each of the major pelvic reconstructions, and interpretations from these are made.
Although firm conclusions are impossible on the limited data available, the evidence suggests that birth in australopithecines was unlikely to have been as difficult as in modern humans.
A triumph for New Labour? Mechanisms of birth in Australopithecus afarensis
Paper given at the 1999 British Association of Biological Anthropology and Osteoarchaeology (BABAO) Conference, University of Birmingham
Emma
C. Nelson
Three factors affect the process of parturition: the fetus, the maternal pelvis, and their relationship. These components are not fixed, as there are physiological, morphological and behavioural mechanisms which can increase the space in the birth canal, thus modifying the cephalo-pelvic relationship. Specifically, these are hormonal affects of pregnancy, posture during birth and, at least in humans, moulding of the fetal head- Birth mechanisms have been widely studied in modern humans, but remain obscure in extinct hominids. Among our Pliocene antecedents, neonatal cranial remains have not yet been recovered. The 3.18 Myr A.L. 288-1 (Lucy) specimen, included in the hypodigm. of Australopithecus afarensis, provides the only pelvis from which all relevant obstetric measurements can be obtained.
The temporal success of A. afarensis, which lasted at least 800 Kyr, demonstrates reproductive success for this taxon. Since successful parturition is a sine qua non of Darwinian fitness, and hominids are K-selected, strong selection pressure will have operated upon the birth process. At the same time, however, the pelvic adaptations associated with bipedality severely compromised the birth canal in a way deleterious to the cephalo-pelvic relationship. Thus, there were probably other adaptations to facilitate birth.
Neonatal size, especially the cranium, is of critical
importance, but we lack fossil evidence. The chimpanzee model is probably
closest among extant primates, but is not ideal. Relative to A.L 288-1, female
chimpanzees possess a larger body mass. Furthermore, Lucy probably represents a
small female A, afarensis, and this taxon displayed greater sexual dimorphism
than modern chimpanzees. However, because neonatal size is related to maternal
size, both between and within primate taxa, it is reasonable to assume that the
neonatal size of Lucy was smaller than the mean chimpanzee neonate. This also
holds for a larger male A. afarensis neonate.
The degree of cranial moulding in A. afarensis is unknown. It does not need to
occur in chimpanzee neonates as the birth canal is spacious, but it does occur
in modern humans. Significant cranial moulding probably paralleled the dramatic
brain size increase observed in later hominids, but this adaptation may have
been necessary even in early hominids given that the maternal pelvis had already
altered for bipedality. Often overlooked as a site of potential cranial moulding
are the mastoid fontanelles, which remain open at birth in humans and other
primates.
In contrast to the lack of evidence surrounding neonatal factors, there is much
contemporary morphological and physiological primate data which can be applied
to the birth process in A.L. 288-1. The hormonal environment of pregnancy would
have permitted pelvic moulding and should also be considered.
We modelled the passage of a scaled, flexed neonatal cranium through the true pelvis of Lucy, and accounted for soft tissue and some maternal pelvic moulding. We found birth would have been easy relative to modem humans, and this could have been further ameliorated by behavioural adaptations evident in other primate species, such as a squatting birth position. These results accommodate the observation of reproductive success evident in A. afarensis.
Emma Nelson M.Phil. 2000
Core work for Palaeolithic archaeologists is the reconstruction of behaviours associated with landscape exploitation from evidence of material remains. Although decision making models, based on modern humans and concerned with the fundamental needs of food and water, have proven to be especially instructive, less effort has been made by archaeologists to understand the relationship between movement on the landscape and the physiological cost to the individual and group.
Energy costs of movement have usually been calculated as a function of time and distance over a constant landscape. In reality, however, neither the landscape nor the activities carried out on the landscape are constant, but highly variable. It is this variability which impacts on time, distance, energy and water relationships. Furthermore, the effects on energy and water balance of movement through time and space, mean that physiological constraints must affect behaviour, which in turn may create a need to evolve novel strategies which facilitate landscape exploitation. Such strategies must have had a bearing on reproductive fitness which may ultimately have led to speciation in our own hominid ancestors.
This pilot-study addresses the energetic and water costs of a small group of individuals surveying the archaeologically significant Makapansgat Valley, South Africa. The aim of the research was to use a simple behavioural model to investigate the effects of movement in a real environment on energy expenditure and water intake and make a preliminary attempt at formulating a costing model using energy and fluid intake as currencies.
Heart rate monitoring provided a measure of group energy expenditure , allowing a costing model based on activity type and duration to be constructed. Preliminary results proved favourable (+ 15%) when tested against the original data. Formal testing now needs to be carried out to corroborate or refute its predictability. Unlike energy expenditure, fluid intake over the day was found to be a poor reflector of movement on the landscape, although good hydration before setting off appeared to have a positive correlation with distance travelled.
Makapansgat Middle Pleistocene Research Project
This project is concerned with understanding the nature of hominin behaviour during the Middle Pleistocene, employing the environmental and archaeological resources of the Makapan Valley as a focus for this investigation.
Understand the hominins and their archaeology at this time poses some fundamental interpretive challenges: the study of hominin mental capacities during the Mid-Pleistocene cannot easily draw upon the modern analogues of either contemporary human hunter-gather societies or modern ape populations. Instead techniques must be developed which can identify and investigate intelligent and strategic behaviour in its own right, from ‘first principles’.
The MMPRP is an inter-diciplinary scientific project and aims to look at the changing nature of human use of environmental resources through the Middle Pleistocene in the Makapan Valley and surrounding environs. By investigating the use of environmental resources, their acquisition, use of these resources, and the implications for the organisation of human groups during the period.
In the longer term the aims of the project include the production of two major monograph volumes on the archaeology of Middle Pleistocene hominins in the area.
Understanding hominid landscapes at Makapansgat, South Africa
Sinclair, A.G.M., McCraith, L. and Nelson, E.
In Michell, P., Haour, A. and Hobart. J. (Eds). Researching Africa’s Past. Oxford University School of Archaeology Monograph No. 57. Oxbox Books
The Makapansgat Middle Pleistocene Research Project has been investigating hominid land use patterns in the immediate vicinity of the Cave of Hearths, Makapansgat, South Africa. Field survey of a 15 km2 area around the cave reveals a range of large and mini sites, as well as a spread of individual find spots. Some of this pattern relates to post-depositional processes at work in the landscape, but other aspects may include hominids’ perceptions of the ease of movement around the landscape and their preference for particular land features.
Two
experimental research projects to help us understand hominid perceptions of
landscapes are reported. One project draws on research in environmental
psychology suggesting humans (and hominids) may have particular preferences for
understanding and exploring landscapes. The other focuses on the energetics of
movement in traversing and foraging in this landscape, as measured by
heart-rate. Initial results indicate that it is difficult to predict energy
expenditure on the basis of distance travelled, but possible on the basis of
time spent engaged
in particular activities.
African Genesis: A symposium on hominid evolution in Africa. Eds: Reynolds, S., Menter, C.G., Robinson, M.S. and Hemmingway. University of Witwatersrand, Johannesburg, South Africa. ISBN 0-620-35737-1
There is evidence in humans that the length ratio of the 2nd and 4th digits (2D:4D) is negatively correlated with prenatal testosterone (PT), and low male 2D:4D is associated with higher fertility and more successful male-male competitive behaviours. Human marriage systems may influence mean 2D:4D such that polygynous societies show high PT (low 2D:4D) while monogamous groups show low PT (high 2D:4D). Here we ask whether similar patterns of mean 2D:4D are evident in the mating systems of non-human primates.
The lengths of the 2nd and 4th digits from both hands were obtained from 276 anaesthetised captive primates (102 males). Mean 2D:4D was 0.839+/-0.072 for the right hand and 0.840+/-0.074 for the left, lower than typical human mean 2D:4D (0.98 to 1.00). Two-factor ANOVA with factors for sex (male, female) and taxon (Apes, Old World Monkeys, New World Monkeys, Prosimians) with dependent variable right 2D:4D showed a significant main effect for taxon (F=20.80, p=0.0001) and non-significant effects for sex and the interaction. Apes had the highest mean 2D:4D (0.915). We excluded Prosimians and performed a two-factor ANOVA (sex [male, female]) and mating system [1=low intensity, low frequency mating to 4=high intensity, high frequency mating]) with dependent variable right 2D:4D. There was a significant main effect for mating system (F=9.19, p=0.0001) with a reduction in mean 2D:4D with increasing competition for mates (1=0.906, 2=0.871, 3=0.853, 4=0.837). There were no significant sex or interaction effects.
We tentatively suggest that, on the evidence of 2D:4D, non-human primates have higher PT (lower 2D:4D) than humans, PT varies between taxa with the lowest PT (higher 2D:4D) found among Apes, and PT reduces with reducing sexual selection such that the lowest PT (highest 2D:4D) is found in mating systems with low intensity/low frequency mating. We consider the effects of lowered PT on human social evolution.