Heterochronic processes in human evolution: an ontogenetic analysis of the hominid pelvis

Publication Trends in the Pelvic Parameter Related Literature between 1992 and 2022 : A Bibliometric Review

OBJECTIVE

This study aimed to conduct a bibliometric analysis on pelvic parameter related research over the last 30 years, analyzing trends, hotspots, and influential works within this field.

METHODS

A comprehensive Web of Science database search was performed. The search yielded 3249 results, focusing on articles and reviews published from 1992 to 2022 in English. Data was analyzed using CiteSpace and VOSviewer for keyword, authorship, and citation burst analysis, co-citation analysis, and clustering.

RESULTS

The number of publications and citations related to pelvic parameters has increased exponentially over the last 30 years. The USA leads in publication count with 1003 articles. Top publishing journals include the European Spine Journal, Spine, and Journal of Neurosurgery: Spine, with significant contributions by Schwab, Lafage V, and Protoptaltis. The most influential articles were identified using centrality and sigma values, indicating their role as key articles within the field. Research hotspots included spinal deformity, total hip arthroplasty, and sagittal alignment.

CONCLUSION

Interest in pelvic parameter related research has grown significantly over the last three decades, indicating its relevance in modern orthopedics. The most influential works within this field have contributed to our understanding of spinal deformity, pelvic incidence, and their relation to total hip arthroplasty. This study provides a comprehensive overview of the trends and influential research in the field of pelvic parameters.

The immature Homo naledi ilium from the Lesedi Chamber, Rising Star Cave, South Africa

Objectives

Homo naledi is represented by abundant remains from the Dinaledi Chamber of the Rising Star Cave system in South Africa. While pelvic elements from the Dinaledi Chamber of the cave are fragmentary, a relatively complete ilium (U.W. 102a–138) was recovered from the Lesedi Chamber. We reconstructed and analyzed the Lesedi ilium, providing qualitative descriptions and quantitative assessment of its morphology and developmental state.

Materials and Methods

We compared the Lesedi ilium to remains from the Dinaledi Chamber, other South African hominin fossils, and an ontogenetic series of human ilia. We used the Dinaledi adults as a guide for reconstructing the Lesedi ilium. To assess development of the Lesedi ilium, we compared immature/mature proportional ilium height for fossils and humans. We used 3D geometric morphometrics (GMs) to examine size and shape variation among this sample.

Results

The Lesedi ilium showed incipient development of features expressed in adult H. naledi ilia. The proportional height of the Lesedi ilium was within the range of human juveniles between 4–11 years of age. GM analyses showed that the Lesedi ilium had an iliac blade shape similar to those of australopiths and an expanded auricular surface more similar to humans.

Conclusions

The reconstructed Lesedi specimen represents the best preserved ilium of H. naledi, confirming the australopith‐like iliac blade morphology first hypothesized in adult specimens, and establishing that this anatomy was present early in this species' ontogeny. In contrast to australopiths, the Lesedi ilium displays an enlarged sacroiliac joint, the significance of which requires further investigation.

Does cranial incidence angle have a role in the tendency toward cervical degenerative disc disease?

Purpose:

The purpose is to investigate if a correlation existed between the frequency of cervical degenerative disc disease occurrence and cranial incidence (CI) angle.

Materials and Methods:

A retrospective analysis of case series. Sagittal parameters of the case series were compared with the sagittal parameters of the same number of consecutive patients with neck pain only but no cervical degenerative disc disease (CDDD). Moreover, CI angle values were noted to be significantly different among groups on variable-based examination. Furthermore, the cervical lordosis (CL) values of men were observed to be significantly different. Therefore, the significant intergroup differences related to the CI angle and CL values support the study hypothesis.

Results:

No intergroup differences were noted regarding gender and age distribution (p = 0.565; p = 0,498). A significant intergroup difference was observed regarding CS values and the mean vector of CI angle and CL values for men and women (p = 0.002). CI angle values were noted to be significantly different among groups upon variable-based examination (p < 0.001). The CL values of men were observed to be significantly different, but not the CL values of women (p = 0.850). Therefore, the significant intergroup differences related to the CI angle and CL values support the study hypothesis.

Conclusions:

A reverse correlation between CI angle and CDDD development is demonstrated. This correlation is valid between CL and CDDD development. Therefore, cervical sagittal profile and the CI angle and CL measurements should be performed to follow-up patients with cervical pain.

A geometric morphometric assessment of shape variation in adult pelvic morphology

OBJECTIVES

In humans, the pelvis is the most sexually dimorphic skeletal element and is often utilized in aging and sexing remains. The pelvis has become greatly relied upon in anthropological research (e.g., forensics, demographics, obstetrics, evolutionary history); however, pelvis morphology is highly variable, and very little is known about the nature, sources, patterning, and interpretation of this variation. This study aims to quantify pelvis shape variation, document sexual shape variation, and estimate the plasticity of morphology. This will ultimately give greater ability to interpret modern, archaeological, and evolutionary patterns to gain deeper insight into processes which shape human anatomy.

MATERIALS AND METHODS

Using a sample of 129 Medieval Danish skeletons, shape variation is documented in the greater sciatic notch (GSN), iliac crest (IC), arcuate line (AL), and sub-pubic angle (SPA) using 3D geometric morphometrics. The landmarking method applied here has the advantage of being applicable to fragmentary remains, rather than requiring whole bones. This allows it to be easily applied to archaeological samples and for the interpretation of separate bone features. Differences in shape were statistically analyzed by principle component analysis, linear discriminate analysis, and morphological disparity. Relationships between maximum femur length, body mass, and shape centroid size were also test by allometric regression.

RESULTS

Results quantify the sexual dimorphism and shape variation present in these features. The GSN shape is the most variable, while the AL is the least. Similarly, the IC is the only feature which shows almost no dimorphism in shape, and instead best reflects lifestyle/activity patterns. Evidence of dimorphism in the IC is likely a result of cultural labor patterns rather than genetic and hormonal influence. Finally, the shapes of the GSN, AL, and SPA are more related to body mass than to femur length, such that individuals with increased mass exhibit more classically "male" shapes and those with less mass have more "female" shapes.

DISCUSSION

The results have important implications for the evolution of pelvic anatomy, and sexual dimorphism, but also highlight the plasticity inherent in pelvic morphology. Analyzing pelvis features separately in a clearly defined, relatively genetically homogenous population gives insight into the determinants of bone morphology, which are not readily observable by other means. The relationship between body mass and shape suggests dimorphism in body size and composition may affect bone shape.

Revisiting thoracic kyphosis: a normative description of the thoracic sagittal curve in an asymptomatic population

PURPOSE

Thoracic kyphosis (TK) remained in the shadow of lumbar lordosis. Based on Berthonnaud and Roussouly segmentation, TK is divided into two arches: upper TK (UTK) and lower TK (LTK). The purpose of this study is to propose a normative description of the TK arches in an asymptomatic adults' population and their correlation with spinal and pelvic parameters.

METHODS

This is an observational study performed on asymptomatic healthy Caucasians volunteers aged between 18 and 45 years. Each patient had a standardized standing biplanar full spine X-rays. Using KEOPS^®, sacropelvic parameters and global spinal parameters (LL, TK) as well as the inflexion point location were measured. The upper lumbar lordosis angle (ULL) as well as LTK and UTK was calculated. Patients were classified according to Roussouly morphotypes of normal spine.

RESULTS

A total of 373 adults (F/M = 1.4/1) were enrolled with mean age of 27 years. Mean UTK averaged 25.8°, while mean LTK averaged 19.8° (p < 0.001). UTK angle values were statistically the same in the five different Roussouly spinal shapes (p > 0.05), while LTK values were variable among different Roussouly spine subtypes (p < 0.05). Finally, TK showed the highest correlation with the LL mainly with the ULL (Pearson = 0.66).

CONCLUSION

In asymptomatic young adults, thoracic kyphosis is composed by two unequal arches, a stable UTK and a variable LTK, with an apex around T8 and T9 vertebra, depending on the spinal morphotype according to Roussouly classification. This should be taken into consideration when analyzing spine sagittal compensation and preparing corrections to minimize risk of mechanical complications.

The influence of long-term shoulder loading on sagittal spino-pelvic morphology: a population-based retrospective study of Chinese farmers from radiology

Background

To investigate associations between long-term shoulder loading and sagittal spino-pelvic morphology in Chinese farmers from radiology evidences.

Methods

We retrospectively analyzed 463 back pain patients who attended outpatient and inpatient departments of two hospitals from January 2016 to December 2018, and who had long, standing lateral X-rays according to inclusion and exclusion criteria. One hundred eighty-four of them were farmers with a long history of heavy shoulder loading for over 20 years in their young age, while others were office workers with no reported long-term shoulder loading history. The following parameters were measured by three researchers independently and then analyzed statistically: thoracic kyphosis (TK), lumbar lordosis (LL), thoracolumbar kyphosis (TLK), T9 sagittal offset (T9SO), T1 sagittal offset (T1SO), sacral slope (SS), pelvic incidence (PI), pelvic tilt (PT), C7 tilt (C7T), spino-pelvic angle (SSA), and sagittal vertical axis (SVA).

Results

The “Loading group” included 86 males and 98 females with average age 73.3 (SD 8.3) years, whereas the “Non-loading group” included 126 males and 153 females with average age 63.7 (SD 14.1) years. Age was significantly higher in the loading group (p < 0.001), but gender, height, weight, BMI, and BMD were not significantly different (p > 0.05). The following spino-pelvic parameters were significantly greater (p < 0.05) in the loading group: TK (mean 39.1° vs 32.8°), TLK (25.8° vs 10.1°), and T9SO (12.2° vs 10.1°). Other values were not significantly different between the two groups (p > 0.05).

Conclusion

Long-term shoulder loading in youth is a risk factor for pathological thoracic kyphosis especially in the lower thoracic spinal segments when farmers getting older.

Mosaic evolution, preadaptation, and the evolution of evolvability in apes

A major goal in postsynthesis evolutionary biology has been to better understand how complex interactions between traits drive movement along and facilitate the formation of distinct evolutionary pathways. I present analyses of a character matrix sampled across the haplorrhine skeleton that revealed several modules of characters displaying distinct patterns in macroevolutionary disparity. Comparison of these patterns to those in neurological development showed that early ape evolution was characterized by an intense regime of evolutionary and developmental flexibility. Shifting and reduced constraint in apes was met with episodic bursts in phenotypic innovation that built a wide array of functional diversity over a foundation of shared developmental and anatomical structure. Shifts in modularity drove dramatic evolutionary changes across the ape body plan in two distinct ways: (1) an episode of relaxed integration early in hominoid evolution coincided with bursts in evolutionary rate across multiple character suites; (2) the formation of two new trait modules along the branch leading to chimps and humans preceded rapid and dramatic evolutionary shifts in the carpus and pelvis. Changes to the structure of evolutionary mosaicism may correspond to enhanced evolvability that has a "preadaptive" effect by catalyzing later episodes of dramatic morphological remodeling.

Pre-Surgery Planning of Lower Limbs Major Joints Arthroplasty

BACKGROUND:

Knee and hip joints endoprosthetics are the main surgical method of arthrosis treatment. The epidemiological incidence rate of the disease is growing steadily every year, affecting younger and younger people. Despite the proven tactics of joint endoprosthetics, an important issue is quality planning of surgery.

AIM:

The aim of this research is to develop a device and a method that would contribute to solving the existing challenges of pre-surgery planning of hip endoprosthetics in patients with related pathologies, which have caused compensatory deformation, and making long vertebrarium-pelvis-lower limbs scout images with the patient lying on his back with an axial load in a computer tomography.

METHODS:

Analog X-ray photographs of the pelvis made on film, digital DICOM images, and special planning programs are used for planning. However, according to numerous studies, the disease of the hip joint is not an independently isolated pathology. In most cases, this pathology is accompanied by changes in the lumbar spine. Often, patients prepared for endoprosthetics have a congenital deformity of tarsus or hip segment, which, during the knee, joint endoprosthetics surgery causes difficulties with the installation of an intramedullary guide.

RESULTS:

The results after total knee arthroplasty according to the method modified at the Department showed a reduction of the WOMAC index slightly more than twice down to 37.26 ± 7.92. The number of revision surgeries after endoprosthetics decreased from 5 (5.7%) to 1 (1.1%) for the hip joint, and from 7 (4.3%) to 2 (1.3%) for the knee joint, respectively.

CONCLUSION:

To form a proper guide entry point, it is necessary to assess the segment at the stage of surgery planning and examination of patients, which can be done using the proposed method. To remove the complications during the pre-surgery planning of hip joint endoprosthetics in patients with related pathologies, a device and methods have been developed for obtaining long topograms of the vertebrarium-pelvis-lower limbs complex with the patient lying on his back with the axial load in computer tomography.

The Gluteus Medius Tendon and Its Insertion Sites: An Anatomical Study with Possible Implications for Gluteus Medius Tears

BACKGROUND

Gluteus medius tears are a common hip disorder. Despite this, the etiology of these tears and the anatomical background of the gluteus medius tendon remain unclear. This study aimed to clarify the characteristics of the gluteus medius tendon. We hypothesized that the tendinous portions of the gluteus medius have a nonuniform structure contributing to the tear etiology.

METHODS

Twenty-five hips from 15 Japanese cadavers were analyzed. Twenty-one of the hips were analyzed macroscopically, and the other 4 were analyzed histologically. In all of the specimens, the 3-dimensional (3D) morphology of the greater trochanter was examined using microcomputed tomography (micro-CT). In 10 of the 21 hips analyzed macroscopically, the local thickness of the gluteus medius tendon, detached from the greater trochanter, was measured.

RESULTS

The posterior and anterolateral parts of the gluteus medius tendons were roughly distinguished on the basis of the aspects of the iliac origins. The posterior part of the gluteus medius tendon ran in a fan-like shape and converged onto the superoposterior facet of the greater trochanter. The anterolateral part ran posteroinferiorly toward the lateral facet of the greater trochanter. The thickness was greater in the posterior part than in the anterolateral part, and the border between these 2 parts was relatively thin compared with the other parts. The histological study showed that both the posterior and anterolateral parts inserted onto the greater trochanter via fibrocartilage.

CONCLUSIONS

The gluteus medius tendon consists of thick posterior and thin anterolateral parts, which were identified by the facet or aspect of the bone structures and thinness of their border region.

CLINICAL RELEVANCE

Our findings indicate that, given the nonuniform structure of the gluteus medius tendon, the thin anterolateral part may be more prone to tears than the thick posterior part is and tears may generally be limited to the anterolateral part.

Adolescent elite skiers with and without cam morphology did change their hip joint range of motion with 2 years follow-up

PURPOSE

To investigate how range of motion of the hips and the lumbar spine are affected by continued elite, alpine skiing in young subjects, with and without a magnetic resonance imaging verified cam morphology, in a 2-year follow-up study. The hypothesis is that skiers with cam morphology will show a decrease in hip joint range of motion as compared with skiers without cam, after a 2-year follow-up.

METHOD

Thirty adolescent elite alpine skiers were examined at the baseline (mean age 17.3 ± 0.7 years) and after 2 years. All skiers were examined for the presence of cam morphology (α-angle > 55°) using magnetic resonance imaging at the baseline. Clinical examinations of range of motion in standing lumbar flexion and extension, supine hip flexion, internal rotation, FABER test and sitting internal rotation and external rotation were performed both at the baseline and after 2 years.

RESULTS

Skiers with and without cam morphology showed a significant decrease from baseline to follow-up in both hips for supine internal rotation (right: mean - 13.3° and - 10.9° [P < 0.001]; left: mean - 7.6° [P = 0.004] and - 7.9° [P = 0.02]), sitting internal rotation (right: mean - 9.6° and - 6.3° [P < 0.001]; left: mean - 7.6° [P = 0.02] and - 3.3° [P = 0.008]) and sitting external rotation (right: mean - 16.9° and - 11.4° and left: mean - 17.9° and - 14.5° [P < 0.001]) and were shown to have an increased left hip flexion (mean + 8.4° and + 4.6° [P = 0.004]). Skiers with cam were also shown to have an increased right hip flexion (mean + 6.4° [P = 0.037]). Differences were found between cam and no-cam skiers from baseline to follow-up in the sitting internal rotation in both hips (right: mean 3.25°, left: mean 4.27° [P < 0.001]), the right hip flexion (mean 6.02° [P = 0.045]) and lumbar flexion (mean - 1.21°, [P = 0.009]).

CONCLUSION

Young, elite alpine skiers with cam morphology decreased their internal rotation in sitting position as compared with skiers without the cam morphology after 2 years of continued elite skiing.

LEVEL OF EVIDENCE

II.

Relative lumbar lordosis and lordosis distribution index: individualized pelvic incidence–based proportional parameters that quantify lumbar lordosis more precisely than the concept of pelvic incidence minus lumbar lordosis

OBJECTIVE

The subtraction of lumbar lordosis (LL) from the pelvic incidence (PI) offers an estimate of the LL required for a given PI value. Relative LL (RLL) and the lordosis distribution index (LDI) are PI-based individualized measures. RLL quantifies the magnitude of lordosis relative to the ideal lordosis as defined by the magnitude of PI. LDI defines the magnitude of lower arc lordosis in proportion to total lordosis. The aim of this study was to compare RLL and PI − LL for their ability to predict postoperative complications and their correlations with health-related quality of life (HRQOL) scores.

METHODS

Inclusion criteria were ≥ 4 levels of fusion and ≥ 2 years of follow-up. Mechanical complications were proximal junctional kyphosis/proximal junctional failure, distal junctional kyphosis/distal junctional failure, rod breakage, and implant-related complications. Correlations between PI − LL, RLL, PI, and HRQOL were analyzed using the Pearson correlation coefficient. Mechanical complication rates in PI − LL, RLL, LDI, RLL, and LDI interpreted together, and RLL subgroups for each PI − LL category were compared using chi-square tests and the exact test. Predictive models for mechanical complications with RLL and PI − LL were analyzed using binomial logistic regressions.

RESULTS

Two hundred twenty-two patients (168 women, 54 men) were included. The mean age was 52.2 ± 19.3 years (range 18–84 years). The mean follow-up was 28.8 ± 8.2 months (range 24–62 months). There was a significant correlation between PI − LL and PI (r = 0.441, p < 0.001), threatening the use of PI − LL to quantify spinopelvic mismatch for different PI values. RLL was not correlated with PI (r = −0.093, p > 0.05); therefore, it was able to quantify divergence from ideal lordosis for all PI values. Compared with PI − LL, RLL had stronger correlations with HRQOL scores (p < 0.05). Discrimination performance was better for the model with RLL than for PI − LL. The agreement between RLL and PI − LL was high (κ = 0.943, p < 0.001), moderate (κ = 0.455, p < 0.001), and poor (κ = −0.154, p = 0.343), respectively, for large, average, and small PI sizes. When analyzed by RLL, each PI − LL category was further divided into distinct groups of patients who had different mechanical complication rates (p < 0.001).

CONCLUSIONS

Using the formula of PI − LL may be insufficient to quantify normolordosis for the whole spectrum of PI values when applied as an absolute numeric value in conjunction with previously reported population-based average thresholds of 10° and 20°. Schwab PI − LL groups were found to constitute an inhomogeneous group of patients. RLL offers an individualized quantification of LL for all PI sizes. Compared with PI − LL, RLL showed a greater association with both mechanical complications and HRQOL. The use of RLL and LDI together, instead of PI − LL, for surgical planning may result in lower mechanical complication rates and better long-term HRQOL.

Range of Hip Joint Motion Is Correlated With MRI-Verified Cam Deformity in Adolescent Elite Skiers

BACKGROUND

Radiologically verified cam-type femoroacetabular impingement (FAI) has been shown to correlate with reduced internal rotation, reduced passive hip flexion, and a positive anterior impingement test.

PURPOSE

To validate how a clinical examination of the hip joint correlates with magnetic resonance imaging (MRI)-verified cam deformity in adolescents.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

The sample group consisted of 102 adolescents with the mean age 17.7 ± 1.4 years. The hip joints were examined using MRI for measurements of the presence of cam (α-angle ≥55°) and clinically for range of motion (ROM) in both supine and sitting positions. The participants were divided into a cam and a noncam group based on the results of the MRI examination. Passive hip flexion, internal rotation, anterior impingement, and the FABER (flexion, abduction, and external rotation) test were used to test both hips in the supine position. With the participant sitting, the internal/external rotation of the hip joint was measured in 3 different positions of the pelvis (neutral, maximum anteversion, and retroversion) and lumbar spine (neutral, maximum extension, and flexion).

RESULTS

Differences were found between the cam and noncam groups in terms of the anterior impingement test (right, P = .010; left, P = .006), passive supine hip flexion (right: mean, 5°; cam, 117°; noncam, 122° [P = .05]; and left: mean, 8.5°; cam, 116°; noncam, 124.5° [P = .001]), supine internal rotation (right: mean, 4.9°; cam, 24°; noncam, 29° [P = .022]; and left: mean, 4.8°; cam, 26°; noncam, 31° [P = .028]), sitting internal rotation with the pelvis and lumbar spine in neutral (right: mean, 7.95°; cam, 29°; noncam, 37° [P = .001]; and left: mean, 6.5°; cam, 31.5°; noncam, 38° [P = .006]), maximum anteversion of the pelvis and extension of the lumbar spine (right: mean, 5.2°; cam, 20°; noncam, 25° [P = .004]; and left: mean, 5.85°; cam, 20.5; noncam, 26.4° [P = .004]), and maximum retroversion of the pelvis and flexion of the spine (right: mean, 8.4°; cam, 32.5°; noncam, 41° [P = .001]; and left: mean, 6.2°; cam, 36°; noncam, 42.3° [P = .012]). The cam group had reduced ROM compared with the noncam group in all clinical ROM measures.

CONCLUSION

The presence of cam deformity on MRI correlates with reduced internal rotation in the supine and sitting positions, passive supine hip flexion, and the impingement test in adolescents.

The Omo-Kibish I pelvis

Omo-Kibish I (Omo I) from southern Ethiopia is the oldest anatomically modern Homo sapiens skeleton currently known (196 ± 5 ka). A partial hipbone (os coxae) of Omo I was recovered more than 30 years after the first portion of the skeleton was recovered, a find which is significant because human pelves can be informative about an individual's sex, age-at-death, body size, obstetrics and parturition, and trunk morphology. Recent human pelves are distinct from earlier Pleistocene Homo spp. pelves because they are mediolaterally narrower in bispinous breadth, have more vertically oriented ilia, lack a well-developed iliac pillar, and have distinct pubic morphology. The pelvis of Omo I provides an opportunity to test whether the earliest modern humans had the pelvic morphology characteristic of modern humans today and to shed light onto the paleobiology of the earliest humans. Here, we formally describe the preservation and morphology of the Omo I hipbone, and quantitatively and qualitatively compare the hipbone to recent humans and relevant fossil Homo. The Omo I hipbone is modern human in appearance, displaying a moderate iliac tubercle (suggesting a reduced iliac pillar) and an ilium that is not as laterally flaring as earlier Homo. Among those examined in this study, the Omo I ischium is most similar in shape to (but substantially larger than) that of recent Sudanese people. Omo I has features that suggest this skeleton belonged to a female. The stature estimates in this study were derived from multiple bones from the upper and lower part of the body, and suggest that there may be differences in the upper and lower limb proportions of the earliest modern humans compared to recent humans. The large size and robusticity of the Omo I pelvis is in agreement with other studies that have found that modern human reduction in postcranial robusticity occurred later in our evolutionary history.

The postcranial skeletal maturation of Australopithecus sediba

OBJECTIVES

In 2008, an immature hominin defined as the holotype of the new species Australopithecus sediba was discovered at the 1.9 million year old Malapa site in South Africa. The specimen (MH1) includes substantial post-cranial skeletal material, and provides a unique opportunity to assess its skeletal maturation.

METHODS

Skeletal maturity indicators observed on the proximal and distal humerus, proximal ulna, distal radius, third metacarpal, ilium and ischium, proximal femur and calcaneus were used to assess the maturity of each bone in comparison to references for modern humans and for wild chimpanzees (Pan troglodytes).

RESULTS

In comparison to humans the skeletal maturational ages for Au. sediba correspond to between 12.0 years and 15.0 years with a mean (SD) age of 13.1 (1.1) years. In comparison to the maturational pattern of chimpanzees the Au. sediba indicators suggest a skeletal maturational age of 9-11 years. Based on either of these skeletal maturity estimates and the body length at death of MH1, an adult height of 150-156 cm is predicted.

DISCUSSION

We conclude that the skeletal remains of MH1 are consistent with an ape-like pattern of maturity when dental age estimates are also taken into consideration. This maturity schedule in australopiths is consistent with ape-like estimates of age at death for the Nariokotome Homo erectus remains (KMN-WT 15000), which are of similar postcranial immaturity to MH1. The findings suggest that humans may have distinctive and delayed post-cranial schedules from australopiths and H. erectus, implicating a recent evolution of somatic and possibly life history strategies in human evolution.

Numerical evaluation of the correlation between the normal variation in the sagittal alignment of the lumbar spine and the spinal loads

We present a numerical approach to reproduce various patterns of spino-pelvic organization. We wanted to predict the spinal loads in two static conditions (standing and holding a weight in the hands) based on parameters describing the shape of the lumbar spine: type following Roussouly classification, sacral slope, apex, inflection point and lumbar lordosis. Four hundred eighty finite element models including trunk muscles and representing the entire range of normal variability were created. The models predicted that, in the case of a moderate external load of 50 N, a lordotic and well balanced spine (e.g., type 3) could reduce the muscle activation in comparison with a more lordotic (type 4) spine, with negligible differences compared to a more straight spine (type 2). However, such a sagittal configuration was not correlated with a minimization of the loading state in the intervertebral discs, especially regarding anteroposterior shear loads. In the standing posture without any additional load, a less lordotic and more vertical spine (e.g., types 1 and 2) was sufficient to ensure a condition of minimal spinal loads. Despite a number of limitations, inverse statics numerical models of spine biomechanics including trunk muscles appear to be a promising tool to fill the knowledge gap between the clinical observations of the correlations between the spino-pelvic organization and the consequent spinal disorders.

The sagittal pelvic thickness: a determining parameter for the regulation of the sagittal spinopelvic balance

Objective. To propose and validate a dimensional parameter, the sagittal pelvic thickness (SPT) (distance between the middle point of the upper sacral plate and the femoral heads axis, expressed as a ratio with the length of the upper plate of S1: (SPT/S1) for the analysis of the sagittal balance of the pelvispinal unit. Methods. The parameters were analysed on standing radiographic imaging and compared for normal, low back pain, children, and spondylolysis cases. Results. Values of SPT/S1 were observed significantly higher in high grade spondylolysis populations and in children (3,5 and 3,7) than in normal population (3,3). A geometrical connection with the classical angular parameters validated SPT/S1. Conclusion. SPT/S1 was considered reflecting the lever arm of action of spinopelvic muscles and ligaments and describing the ability of a subject to compensate a sagittal unbalance. It was proposed as an anatomical and functional pelvic parameter.

Influence of sagittal balance on spinal lumbar loads: a numerical approach

BACKGROUND

Pathological deformities involving the sagittal alignment of the spine may lead to loss of spine stability and imbalance. The effect of different patterns of sagittal balance on the loads acting in the spine was only marginally investigated, although it would be of critical importance in the clinical management of spinal disorders.

METHODS

Optimization-based finite element models of the human spine in the standing position able to predict the loads acting in the lumbar spine and the activation of the spinal muscles were developed and used to explore a wide range of sagittal balance conditions, covering both inter-subject variability and pathological imbalance. 1000 two-dimensional randomized spine models with simplified geometry were generated by varying anatomical parameters such as lumbar lordosis, sacral slope, and C7 plumb line. Muscular loads were calculated by means of an optimization procedure aimed to minimize total muscular stress.

FINDINGS

The simulation of a physiological spine in the standing position predicted average disk stresses ranging from 0.38 to 0.5MPa, in good agreement with in vivo measurements. The C7 plumb line and the parameters describing the lumbar spine were found to be the strongest determinants of the lumbar loads and muscle activity. Marginal relevance was found concerning the thoracic and cervical parameters.

INTERPRETATION

The present modeling approach was found to be able to capture correlations between sagittal parameters and the loads acting in the lumbar spine. The method represents a good platform for future improvements aimed at patient-specific modeling to support pre-operative surgical planning.

Effect of maternal and grandmaternal care on population dynamics and human life-history evolution: a matrix projection model

We present a matrix population model for a single-sex human population comprising non-orphan daughters (whose mothers are alive) and orphan daughters (whose mothers are dead). Orphans suffer higher mortality than non-orphans, which simulates the need for daughters to receive maternal care in order to survive. The way that maternal care affects population dynamics and life-history evolution is then analysed for demographic regimes that encompass large ranges of daughter survival, mother survival and fertility. We provide stable age-distributions of orphans and non-orphans for each regime and perform sensitivity analyses on daughter survival, adult survival and fertility. The results show that natural selection will favour (i) faster daughter independence from maternal care, (ii) higher adult survival at all ages, and (iii) early reproduction to the detriment of late reproduction. We then build scenarios concerning the coevolution of daughter survival and maternal care with adult survival and fertility. We also incorporate grandmaternal care into the model. We show that (i) the acute altriciality of human babies, (ii) the increased maternal care resulting from emergence of complex sociality and (iii) the role played by grandmothers in caring for granddaughters may have led to the emergence of specific human life-history traits: a short reproductive period characterised by a reproductive senescence and menopause, as well as an extended lifespan characterised by a post-reproductive life.

Pelvic parameters: origin and significance

INTRODUCTION

The adoption by humans of an upright position resulted in broadening and verticalisation of the pelvis together with the appearance of characteristic spinal curves, has profoundly modified the structure of the muscles supporting the spine.

MATERIAL

In order to characterise the sagittal balance of the pelvis, it is necessary to define parameters based on notable biomechanical forces involved in the transmission of constraints. The angle of incidence was constructed to enable reproducible analysis of the anatomical characteristics of the pelvis in the sagittal plane. The angle of incidence is the algebraic sum of two complementary angles: pelvic tilt (PT) and sacral slope (SS). Since the value of incidence is fixed for any given patient, the sum of pelvic tilt and sacral slope is a constant value: when one increases, the other necessarily decreases.

RESULT

The position of the lumbar spine, attached to the sacral plateau, is thus affected by the pelvic tilt and by the sacral slope. Consequently, the pelvic parameters affect the entire underlying sagittal spinal profile.

CONCLUSION

Global spinal balance involves harmonisation of lumbar lordosis and thoracic kyphosis taking into account the pelvic parameters.

Equilibrium of the human body and the gravity line: the basics

INTRODUCTION

Bipedalism is a distinguishing feature of the human race and is characterised by a narrow base of support and an ergonomically optimal position thanks to the appearance of lumbar and cervical curves.

MATERIALS

The pelvis, adapted to bipedalism, may be considered as the pelvic vertebra connecting the spine to the lower limbs. Laterally, the body's line of gravity is situated very slightly behind the femoral heads laterally, and frontally it runs through the middle of the sacrum at a point equidistant from the two femoral heads.

RESULTS

Any abnormal change through kyphosis regarding the spinal curves results in compensation, first in the pelvis through rotation and then in the lower limbs via knee flexion. This mechanism maintains the line of gravity within the base of support but is not ergonomic. To analyse sagittal balance, we must thus define the parameters concerned and the relationships between them.

CONCLUSION

These parameters are as follows: for the pelvis: incidence angle, pelvis tilt, sacral slope; for the spine: point of inflexion, apex of lumbar lordosis, lumbar lordosis, spinal tilt at C7; for overall analysis: spino-sacral angle, which is an intrinsic parameter.

Ontogenetic changes in the internal and external morphology of the ilium in modern humans

Trabecular architecture forms an important structural component of bone and, depending on the loading conditions encountered during life, is organised in a systematic, bone- and species-specific manner. However, recent studies suggested that gross trabecular arrangement (e.g. density distribution), like overall bone shape, is predetermined and/or affected by factors other than loading and perhaps less plastic than commonly assumed. To explore this issue further, the present cross-sectional ontogenetic study investigated morphological changes in external bone shape in relation to changes in trabecular bundle orientation and anisotropy. Radiographs of 73 modern human ilia were assessed using radiographic and Geometric Morphometric techniques. The study confirmed the apparently strong predetermination of trabecular bundle development, i.e. prior to external loading, although loading clearly also had an effect on overall morphology. For example, the sacro-pubic bundle, which follows the path of load transmission from the auricular surface to the acetabulum, is well defined and shows relatively high levels of anisotropy from early stages of development; the situation for the ischio-iliac strut is similar. However, while the sacro-pubic strut retains a constant relationship with the external landmarks defining the joint surfaces, the ischio-iliac bundle changes its relationship with the external landmarks and becomes aligned with the iliac tubercle only during late adolescence/early adulthood. It is tentatively proposed that the rearrangement of the ischio-iliac strut may reflect a change in locomotor pattern and/or a shift in positional behavior with increasing mass after growth of external bone dimensions has slowed/ceased.

Morphological traits in sacra associated with complete and partial lumbarization of first sacral segment

BACKGROUND CONTEXT

Transitional states of vertebrae at the lumbosacral junction are associated with low back pain. Lumbarization may present as partial (incomplete separation of S1-S2 bodies and their neural arches) or complete separation of the S1 from the S2 segment in a sacrum. Separation of S1 entails alteration of the anatomy at the lumbosacral junction that affects load bearing at the region.

PURPOSES

To 1) identify characteristic structural features in sacra associated with lumbarization of the S1 sacral element; 2) compare linear dimensions and surface areas in such sacra with that of the normal samples; 3) calculate relative contributions of different dimensions in the variant sacral corpuses by working out indices; and 4) analyze load bearing at these sacra in light of their altered morphology.

STUDY DESIGN

Three hundred thirty-two dried human sacra were measured for specific dimensions and surface areas. They were screened for partial or complete lumbarization of the S1 segment.

OUTCOME MEASURES

All parameters and indices of the lumbarized specimen were compared with those in the normal sacra.

METHODS

Seven linear dimensions and five surface areas were measured in 332 sacra. Nine indices were formulated from them. Sacra with partial or complete lumbarization of S1 were analyzed for all the parameters and evaluated for their morphological variations and traits.

RESULTS

A total of 3.9% of sacra presented lumbarization, seven (2.1%) with partial and six (1.8%) with complete separation of the S1. Sacrum with partial lumbarization presented parameters similar to the normal variety. Auricular surfaces in these sacra were situated lower than normal with negligible contribution from the S1 segments. Parameters in sacral samples showing complete separation of S1 (with remaining S2-S5 segments) were smaller than normal dimensions except for some. These "baseline" (S2-S5) sacra transmitted load to the sacroiliac joints via the S2 and S3 elements. Four of six of these samples demonstrated unilateral or bilateral accessory facets between the transverse elements of the free S1 segment and the ala of the remaining sacrum (formed by S2). Significant load passed through the accessory articulations that abutted near the sacroiliac joints. A good number of these sacra showed highly attenuated laminae and at times presented incomplete fusion at the spines (spina bifida).

CONCLUSIONS

Lumbarization involved distinct anatomical alterations at the S1-S2 junctions. Partially lumbarized samples showed 1) gap (mean 1.43 mm) between S1 and S2 bodies; 2) incomplete separation between S1 and S2 neural arch elements with the S1 arches resembling lumbar laminae; 3) well-developed "baseline" (S2-S5) segments; and 4) "low-down" (positioned at S2-S3) auricular surfaces. Complete separation of S1 involved 1) smaller overall dimensions with diminished facet depth, sacral height, and facet area at S1; 2) auricular surface areas comparable to the normal and greater than those found in the partially lumbarized specimen; 3) large "baseline" (S2-S5) sacra with "high-up" auricular surfaces (positioned at S2-S3); 4) occasional S1-S2 accessory articulations; and 5) small zygapophyseal joints and attenuated sacral laminae with high sacral hiatuses associated at times, with "spina bifida."

Protection of obstetric dimensions in a small-bodied human sample

In human females, the bony pelvis must find a balance between being small (narrow) for efficient bipedal locomotion, and being large to accommodate a relatively large newborn. It has been shown that within a given population, taller/larger-bodied women have larger pelvic canals. This study investigates whether in a population where small body size is the norm, pelvic geometry (size and shape), on average, shows accommodation to protect the obstetric canal. Osteometric data were collected from the pelves, femora, and clavicles (body size indicators) of adult skeletons representing a range of adult body size. Samples include Holocene Later Stone Age (LSA) foragers from southern Africa (n = 28 females, 31 males), Portuguese from the Coimbra-identified skeletal collection (CISC) (n = 40 females, 40 males) and European-Americans from the Hamann-Todd osteological collection (H-T) (n = 40 females, 40 males). Patterns of sexual dimorphism are similar in the samples. Univariate and multivariate analyses of raw and Mosimann shape-variables indicate that compared to the CISC and H-T females, the LSA females have relatively large midplane and outlet canal planes (particularly posterior and A-P lengths). The LSA males also follow this pattern, although with absolutely smaller pelves in multivariate space. The CISC females, who have equally small stature, but larger body mass, do not show the same type of pelvic canal size and shape accommodation. The results suggest that adaptive allometric modeling in at least some small-bodied populations protects the obstetric canal. These findings support the use of population-specific attributes in the clinical evaluation of obstetric risk.

Ontogeny and Phylogeny of the Pelvis in Gorilla, Pongo, Pan, Australopithecus and Homo

To examine the evolutionary differences between hominoid locomotor systems, a number of observations concerning the growth of the pelvis among the great apes as compared to modern and fossil hominids are reported. We are interested in the size and shape of the coxal bones at different developmental stages across species that may elucidate the relationship between ontogeny and phylogeny (i.e., heterochrony) in the hominoid pelvis. Our hypotheses are: (1) do rates of absolute growth differ?, (2) do rates of relative growth differ?, and (3) does heterochrony explain these differences? Bivariate and multivariate analyses of pelvic dimensions demonstrate both the diversity of species-specific ontogenetic patterns among hominoids, and an unequivocal separation of hominids and the great apes. Heterochrony alone fails to account for the ontogenetic differences between hominids and the great apes. Compared to recent Homo,Australopithecus can be described as 'hyper-human' from the relative size of the ischium, and short but broad ilium. Australopithecus afarensis differs from Australopithecus africanus by its relatively long pubis. In multivariate analyses of ilium shape, the most complete coxal bone attributed to Homo erectus, KNM-ER 3228, falls within the range of juvenile and adult Australopithecus, whereas Broken Hill falls within the range of modern Homo, suggesting that the modern human ilium shape arose rather recently. Among the great apes, patterns of pelvic ontogeny do not exclusively separate the African apes from Pongo.

Cranial growth in normal and low-protein-fed Saimiri. An environmental heterochrony

Protein malnutrition has a significant and measurable effect on the rate and timing of growth. Heterochrony is generally viewed as the study of evolutionary changes in the relative rates and timing of growth and development. Although changes in growth commonly result from experimental manipulations of diet, nobody has previously attempted to explain such changes from a heterochronic perspective. We use a heterochronic perspective to compare a group of squirrel monkeys fed a low-protein diet to individuals on a high-protein diet, but, in contrast to previous works, we focus particularly on the effects of environmental and not genetic factors. In the present study, Gould's (1977) and Godfrey and Sutherland's (1996) methodologies for studying heterochrony, as well as geometric morphometrics, are used to compare two groups of Saimiri sciureus boliviensis. Two groups of Saimiri were constructed on the basis of the protein content in their diets: a high-protein group (HP) (N=12) and a low-protein group (LP) (N=12). All individuals are males born in captivity. Two major functional components of the skull, the neurocranium and the face, were analysed. Four minor components were studied in each major component. Comparison of craniofacial ontogeny patterns based on major and minor components suggests that changes in the skull of LP animals can be explained by heterochrony. The skull of LP animals exhibits isomorphism produced by proportioned dwarfism. Our results suggest that heterochrony can be environmentally, rather than exclusively genetically, induced. The study of genetic assimilation (Waddington, 1953, 1956; see Scharloo, 1991; Hallgrimsson et al., 2002) has demonstrated that environmentally induced phenotypes often have a genetic basis, and thus parallel changes can be easily induced genetically. It is possible that proportioned dwarfism is far more common than currently appreciated.

Évolution anthropologique du bassin osseux des femmes

The existence of dystocia in human presents a vexing problem for an evolutionary point of view. Dealing with the great apes and modern human's pelvis evolution, considering the bipedalism and the cerebral growth, the adaptative mechanisms and their obstetrical and social consequences are discussed.

Meat‐Adaptive Genes and the Evolution of Slower Aging in Humans

The chimpanzee life span is shorter than that of humans, which is consistent with a faster schedule of aging. We consider aspects of diet that may have selected for genes that allowed the evolution of longer human life spans with slower aging. Diet has changed remarkably during human evolution. All direct human ancestors are believed to have been largely herbivorous. Chimpanzees eat more meat than other great apes, but in captivity are sensitive to hypercholesterolemia and vascular disease. We argue that this dietary shift to increased regular consumption of fatty animal tissues in the course of hominid evolution was mediated by selection for "meat-adaptive" genes. This selection conferred resistance to disease risks associated with meat eating also increased life expectancy. One candidate gene is apolipoprotein E (apoE), with the E3 allele evolved in the genus Homo that reduces the risks for Alzheimer's and vascular disease, as well as influencing inflammation, infection, and neuronal growth. Other evolved genes mediate lipid metabolism and host defense. The timing of the evolution of apoE and other candidates for meat-adaptive genes is discussed in relation to key events in human evolution.

Ontogenetic allometry, heterochrony, and interspecific differences in the skull of African apes, using tridimensional Procrustes analysis

Ontogenetic studies of African ape skulls lead to an analysis of morphological differences in terms of allometry, heterochrony, and sexual dimorphism. The use of geometric morphometrics allows us 1) to define size and shape variations as independent factors (an essential but seldom respected condition for heterochrony), and 2) to calculate in percentage of shape changes and to graphically represent the parts of shape variation which are related to various biological phenomena: common allometry, intraspecific allometry, and allometric and nonallometric shape discrimination. Three tridimensional Procrustes analyses and the calculation of multivariate allometries, discriminant functions, and statistical tests are used to compare the skulls of 50 Pan troglodytes, and 50 Gorilla gorilla of different dental stages. The results both complement and modify classical results obtained from similar material but with different methods. Size and Scaling in Primate Morphology, New York: Plenum, p. 175-205). As previously described by Shea, the common growth allometric pattern is very important (64% of total shape variation). It corresponds to a larger increase of facial volume than of neurocranial volume, a more obliquely oriented foramen magnum, and a noticeable reshaping of the nuchal region (higher inion). However, the heterochronic interpretation based on common allometry is rather different from Shea. Gorillas differ from chimpanzees not only with a larger magnitude of allometric change (rate peramorphosis), as is classically said, but also grow more in size than in shape (size acceleration). In other words, for a similar stage of growth, gorillas have the size and shape corresponding to older chimpanzees, and for a similar shape, gorillas have a larger size than chimpanzees. In contrast, sexual dimorphism actually corresponds to allometric changes only, as classically demonstrated (time hypermorphosis). Sexual dimorphism is here significant in adult gorillas alone, and solely in terms of allometry (size-related shape and size, given that sagittal and nuchal crests are not taken into account). The study also permits us to differentiate two different shape variations that are classically confused in ontogenetic studies: a very small part of allometric shape change which is specific to each species (1% of the total shape variation), and nonallometric species-specific traits independent of growth (8% of total shape change). When calculated in terms of intraspecific allometries (including common allometry and noncommon allometry), shape changes are more extensive in gorillas (36% of total shape change) than in chimpanzees (29% of total shape change). The allometric differences mainly concern the inion, which becomes higher; the position of the foramen magnum, more dorsally oriented; and the palate, more tilted in adult gorillas than in adult chimpanzees. In contrast, nonallometric species-specific traits in gorillas are the long and flat vault characterized by a prominent occipital region, the higher and displaced backward glabella, and the protrusive nose. Biomechanical schemes built from shape partition suggest that the increased out-of-plumb position of the head during growth is partially compensated in gorillas by a powerful nuchal musculature due to the peculiar shape of the occipital region.

Haeckel's ABC of evolution and development

One of the central, unresolved controversies in biology concerns the distribution of primitive versus advanced characters at different stages of vertebrate development. This controversy has major implications for evolutionary developmental biology and phylogenetics. Ernst Haeckel addressed the issue with his Biogenetic Law, and his embryo drawings functioned as supporting data. We re-examine Haeckel's work and its significance for modern efforts to develop a rigorous comparative framework for developmental studies. Haeckel's comparative embryology was evolutionary but non-quantitative. It was based on developmental sequences, and treated heterochrony as a sequence change. It is not always clear whether he believed in recapitulation of single characters or entire stages. The Biogenetic Law is supported by several recent studies -- if applied to single characters only. Haeckel's important but overlooked alphabetical analogy of evolution and development is an advance on von Baer. Haeckel recognized the evolutionary diversity in early embryonic stages, in line with modern thinking. He did not necessarily advocate the strict form of recapitulation and terminal addition commonly attributed to him. Haeckel's much-criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution. While some criticisms of the drawings are legitimate, others are more tendentious. In opposition to Haeckel and his embryo drawings, Wilhelm His made major advances towards developing a quantitative comparative embryology based on morphometrics. Unfortunately His's work in this area is largely forgotten. Despite his obvious flaws, Haeckel can be seen as the father of a sequence-based phylogenetic embryology.

Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis

Heterochronic studies compare ontogenetic trajectories of an organ in different species: here, the skulls of common chimpanzees and modern humans. A growth trajectory requires three parameters: size, shape, and ontogenetic age. One of the great advantages of the Procrustes method is the precise definition of size and shape for whole organs such as the skull. The estimated ontogenetic age (dental stages) is added to the plot to give a graphical representation to compare growth trajectories. We used the skulls of 41 Homo sapiens and 50 Pan troglodytes at various stages of growth. The Procrustes superimposition of all specimens was completed by statistical procedures (principal component analysis, multivariate regression, and discriminant function) to calculate separately size-related shape changes (allometry common to chimpanzees and humans), and interspecific shape differences (discriminant function). The results confirm the neotenic theory of the human skull (sensu Gould [1977] Ontogeny and Phylogeny, Cambridge: Harvard University Press; Alberch et al. [1979] Paleobiology 5:296-317), but modify it slightly. Human growth is clearly retarded in terms of both the magnitude of changes (size-shape covariation) and shape alone (size-shape dissociation) with respect to the chimpanzees. At the end of growth, the adult skull in humans reaches an allometric shape (size-related shape) which is equivalent to that of juvenile chimpanzees with no permanent teeth, and a size which is equivalent to that of adult chimpanzees. Our results show that human neoteny involves not only shape retardation (paedomorphosis), but also changes in relative growth velocity. Before the eruption of the first molar, human growth is accelerated, and then strongly decelerated, relative to the growth of the chimpanzee as a reference. This entails a complex process, which explains why these species reach the same overall (i.e., brain + face) size in adult stage. The neotenic traits seem to concern primarily the function of encephalization, but less so other parts of the skull. Our results, based on the discriminant function, reveal that additional structural traits (corresponding to the nonallometric part of the shape which is specific to humans) are rather situated in the other part of the skull. They mainly concern the equilibrium of the head related to bipedalism, and the respiratory and masticatory functions. Thus, the reduced prognathism, the flexed cranial base (forward position of the foramen magnum which is brought closer to the palate), the reduced anterior portion of the face, the reduced glabella, and the prominent nose mainly correspond to functional innovations which have nothing to do with a neotenic process in human evolution. The statistical analysis used here gives us the possibility to point out that some traits, which have been classically described as paedomorphic because they superficially resemble juvenile traits, are in reality independent of growth.

Genetic basis of human female pelvic morphology: a twin study

To examine the relative role of genetic and environmental factors on pelvic morphology, data on 60 pairs of female twins (30 monozygotic (MZ) and 30 dizygotic (DZ)) were analyzed. Fourteen pelvic measurements were normally distributed, and two were not. Association of twin type with the mean value of a trait was found in only 1 out of 8 traits. Heterogeneity of variance between zygosities was observed in 4 pelvic traits (50%), invalidating within-pair estimates of genetic variance for these traits. Evidence of stronger environmental covariance for MZ than DZ twins was observed for only one trait (sitting height iliocristale). A significant genetic component of variation was observed for age at menarche and in the pelvic area. In instances where inequality of variances between zygosities was demonstrated, total among-pair and within-pair mean squares were larger for dizygotic than for monozygotic twins. This is interpreted as evidence of greater environmental influence between zygosities. Environmental modification was not of the same magnitude in various pelvic traits. Bitrochanteric breadth had the highest magnitude of cultural heritability, indicating that cultural factors played an important role in determining hip breadth.

Modeling three-dimensional sculptures of australopithecines (Australopithecus afarensis) for the Museum of Natural History of Vienna (Austria): the post-cranial hypothesis

In March 1999, E. Daynes, a sculptor specializing in fossil hominid reconstruction, asked C. Berge to take over the scientific supervision of the reconstruction of two australopithecine post-crania. The heads had been modeled from two skulls found in Hadar (AL 444-2, AL 417). The sculptures were to be represented in a walking stance. The female proportions (AL 417) are estimated from the skeleton of 'Lucy' (AL 288), and the male proportions (AL 444-2) extrapolated from the female ones. Biomechanical and anatomical data (comparison with great apes and humans) are used to reconstruct both dynamic equilibrium and muscular systems. The reconstruction suggests that the fossils moved the pelvis and shoulders extensively when they walked. The hindlimb muscles (such as adductors, gluteal muscles and calf) are fleshy and not or very little tendinous. As indicated by the Laetoli step prints (belonging to a close and contemporaneous species), the foot is adducted during the walk and the support is internal just before take off. In spite of inevitable approximations, such a reconstruction appears to be particularly helpful to bring out morphological and functional traits of the first hominids which are both close to and different from modern humans.

How did the human brain evolve? A proposal based on new evidence from in vivo brain imaging during attention and ideation

It is proposed that brain evolution in nonhuman primates and humans was facilitated by heritable differences in neuroplasticity and in the number of neurons and synapses available during childhood and adolescence, therefore, in differences in modifiability and elaboration of neuronal networks in brains of immature primate genotypes. These differences were exploited when a primate population was forced to adapt to a new cognitively or behaviorally demanding milieu, to select more cognitively and brain competent adults who could best compete and reproduce in this new milieu, extending their genes within the population. Two recently solidified concepts suggest a mechanism for this evolutionary process: (1) "Association" neocortex can be activated by attention and ideation in the absence of sensory or motor contributions, as demonstrated by in vivo imaging and direct brain recording. (2) Activation of the immature brain can promote and stabilize neuronal networks that would disappear or otherwise lose their function by adulthood. Taking these two ideas together, it is proposed that the "thought" processes of attention and ideation, when used by immature primates to adapt to new cognitive or behavioral stresses, led by the repeated selection of genotype to more cognitively able, larger-brained species with more extensive "association" cortex and related regions.