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Article

The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology

by
Jeanelle Uy
*,
Gabrielė Beresnevičiūtė
and
Vyvy Nguyen
Department of Anthropology, California State University Long Beach, Long Beach, CA 90840, USA
*
Author to whom correspondence should be addressed.
Humans 2024, 4(4), 310-320; https://doi.org/10.3390/humans4040020
Submission received: 7 September 2024 / Revised: 26 September 2024 / Accepted: 27 September 2024 / Published: 1 October 2024
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Abstract

:
Organ–skeleton relationships are understudied in biological anthropology. The torso skeleton is often used to infer the organ size and evolution in hominins; ribcage “types”, in particular, are used to infer the abdominal organ size in hominins. This study is a quantitative examination of the relationship between the lower ribcage and two organs: the liver and the intestines (“gut”) in humans. Specifically, we test whether the ribcage breadth, shape, and “flare”, at the level of rib 10, covaries with the liver volume and gut volume in Homo sapiens. Liver size, gut size, and ribcage measurements are taken from CT scans (N = 61). The results show sex differences in the gut–ribcage relationship. The gut volume is associated with ribcage breadth and flare in both sexes. The liver volume is not associated with any ribcage measurements. We conclude that sex differences in the organ–skeleton relationship complicate the previous simplistic view that the size of the liver or the gut could be inferred through a fossil’s ribcage type. Biological anthropologists should continue to explore sex differences in organ–skeleton relationships, when attempting to understand the evolution of visceral organs and the torso.

1. Introduction

Biological anthropologists have long hypothesized that the ribcage type, namely funnel-shaped or barrel-shaped ribcages, in hominins (and apes) can reflect the size of the abdominal organs. This is a key assumption that led to the development of influential hypotheses in the field, such as the Expensive Tissue Hypothesis and the High-Protein Diet Hypothesis for Neandertals [1,2].
Ribcage types have been used to infer the organ size in extinct hominins, such as in Australopithecus afarensis, Homo erectus, Homo naledi, and Neandertals [1,2,3,4,5]. The idea that the size of the intestines (“gut”) or the liver have changed in the hominin lineage informs narratives about the evolution of diet, locomotion, and the brain, and underlying these narratives is an assumption that a relationship exists between these organs and the torso skeleton [1,2,6,7,8]. The present study directly examines the gut–ribcage and liver–ribcage relationship in humans, offering a quantitative exploration of the conventional wisdom that the torso skeleton reflects the abdominal organ size.
Paleoanthropologists adopted the ribcage typology from Schultz [9], who described the ribcage of apes and monkeys as being funnel- or barrel-shaped, with non-human apes having a more funnel-shaped thorax or “flared” lower ribcage. Humans, according to Schultz’s typology, have a more barrel shape or less flare to their lower ribcage. Chimpanzees, gorillas, and orangutans, on the other hand, have a more funnel shape and more flare to their lower ribcage.
The liver and gut do not fossilize, so paleoanthropologists have inferred liver and gut size evolution by relying on skeletal proxies like the ribcage. For example, Neandertals have been hypothesized to have large liver volumes compared with humans because of their large thoraces, according to the High-Protein Diet Hypothesis [2]. Costal fossil remains indicate Neandertals possessed large, bell-shaped ribcages compared to modern humans, due to their large and broad body, high energy needs, and/or their high-protein diet [2,10,11,12]. Ben-Dor and colleagues hypothesized that because Neandertals were often exposed to low temperatures and likely had high-protein diets during European glacial winters, they probably had enlarged livers, similar to circumpolar human populations today [2]. Because the lower ribcage partially encases the liver, it likely correlates with the size of the liver. In fact, in clinical settings, the thoraco-abdominal circumference has been known to be a good proxy for liver size [13]. However, there are no data linking skeletal measurements with liver size in a way that would be useful for understanding the liver in hominins.
Similarly, the morphology of the lower ribcage is hypothesized to correlate with gut size. When considering the fossil record, the most influential narratives on gut evolution come from the interpretations in terms of the fossil remains of Australopithecus afarensis and Homo erectus. Paleoanthropologists assigned an ape-like, flaring, and funnel-shaped ribcage to A. afarensis, based on fragmentary costal remains from A.L. 288-1, or “Lucy” [3]. Latimer and co-authors [14] suggested a different reconstruction of the A. afarensis ribcage based on the fossil KSD-VP-1/1 (nicknamed “Kadanuumuu”), which shows a more “bell-shaped” ribcage that shows less flaring than a chimp, though still more flaring than a human. Following the findings and analysis of the H. erectus partial skeleton KNM-WT 15,000, or “Nariokotome Boy”, it was suggested that by the time of H. erectus, hominins had a human-like and barrel-shaped ribcage relative to Australopithecus [15]. However, a more recent 3D morphometric analysis shows that KNM-WT 15000 probably had a wider ribcage than originally thought [16]. The original interpretations of the KNM-WT 15,000 thorax and the A.L. 288-1 thorax became components of major theories on dietary change in hominin evolution, such as the Expensive Tissue Hypothesis, the Endurance Running Hypothesis, and the Cooking Hypothesis [1,6,8]. It was thought that the lower ribcage, by shrinking in size and becoming less flared, was indicative of a concordant shrinking of the digestive system. This was based on the observation that apes with flaring lower ribcages have large guts compared to humans, who have the opposite: a non-flaring lower ribcage and small guts [17,18]. According to this interpretation, if a barrel-shaped instead of a funnel-shaped ribcage was observed in hominins, it would indicate a relatively human-like, small gut size. However, hominins, apes, and monkeys display substantial ribcage shape variation, beyond this dichotomy [4,14,19,20,21,22].
Although our understanding of ribcage diversity has advanced considerably in the last decade, our understanding of the relationship between the ribcage and the abdominal organs has not. Today, we know that the ribcage is modular in its development and function; the cranial ribcage is hypothesized to be more sensitive to forelimb locomotor function, while the caudal ribcage is more integrated with the pelvis and possibly the digestive system [19,20,21,23,24,25,26,27,28]. Re-analyses of fossil ribs from A. afarensis and H. erectus, as well as more recent fossil finds, indicate that a mosaic of ribcage forms likely existed in the hominin lineage [4,14,16,22]. Furthermore, the human ribcage exhibits differences according to sex. Male individuals tend to have a more pyramidal thorax compared to female individuals, who tend to have a more cylindrical thorax [29]. This leaves us to question whether abdominal organ sizes should continue to be inferred from the ribcage form, given that ribcage typologies seem to fail to capture the diversity in the thorax shape.
Being able to infer the gut and liver size has profound implications on how biological anthropologists understand human evolution, because these organs are informative about dietary shifts. Few have attempted to empirically test whether the abdominal organ size is associated with the size and morphology of skeletal remains, using extant species. One study by Uy and colleagues found the gut size to vary with the maximum bi-iliac breadth in male individuals, but not in female individuals [30]. In another study looking at iliac flare in apes and monkeys, Boyle and Almécija found that iliac flare correlates with the gut size in apes, though the sample size was quite small (N = 5) [31]. Here, we present an empirical study that tests whether the gut volume and liver volume have significant relationships with the measurements of the lower ribcage (rib 10 specifically) in H. sapiens. Based on our understanding of the relationship between the abdominal organ size and the pelvis [30] and the knowledge that the ribcage is sexually dimorphic [29,32,33], we hypothesize that these abdominal organs have relationships with the ribcage that vary according to sex, just like in the pelvis. We specifically sought to examine the organ volume relationships with the maximum ribcage breadth, ribcage “flare”, and rib curvature angle (which measures the “openness” of an individual rib).

2. Materials and Methods

2.1. Sample Description

To test these hypotheses, we used abdominal computed tomography (CT) scans of living humans (Nfemale = 31, Nmale = 30). The CT scans were previously de-identified for a past study conducted by one of us (J.U.); hence, this study did not require an IRB review. The scans were collected from an archival database at the University of Wisconsin–Madison School of Medicine and Public Health. The scans were selected by the Radiology Department and were from individuals that did not have any observed abnormalities. The dataset represents a sample of adults aged 18–25. Some studies suggest that the length and diameter of the intestines varies throughout the life course [34,35], so we sought a sample with a limited age range, even though not all studies agree on how age affects intestine size [36,37]. The original study that used the dataset was interested in a sample of subjects that were likely to be nulliparous or, at least, low parity; therefore, the subjects were selected from the narrow age range of 18–25. The exclusion criteria benefit the present study as well, due to our interest in sexual dimorphism and the implications for evolved differences related to pregnancy.

2.2. Ribcage Measurements

Three-dimensional images of the lower ribcage were extracted from the CT scans using ITK SNAP 4.0 [38] The CT scans were abdominal scans; therefore, they did not include the entire ribcage. We used rib 10 in our analyses, because it is the caudal-most rib that surrounds the liver and the gut. Rib 10 is also not hypervariable like the 11th and 12th ribs [39]. There is one point to note about the CT scans that posed limitations to our data collection. The scans were originally obtained by the University of Wisconsin School of Medicine Radiology Department to view the abdominal cavity (they were from an archival database, not obtained for this study specifically); only a fraction of the scans contained ribs above rib 11, limiting our sample size. We chose to include in any scans that contained the whole of rib 10 and below. The widest part of the ribcage is around the rib 8 level; while it is possible that higher ribs than rib 10 are more suitable to examine ribcage “flare”, we think that rib 10 is an acceptable level given that it is still relevant to the question concerning the ribcage’s relationship with the abdominal organs. Rib 10 encompasses the bulk of the liver and a larger bulk of the intestines, compared to ribs located higher up. It would be worth investigating a more complete lower ribcage in the future.
Using 3D Slicer 5.6.2 [40], we placed 9 landmarks at the level of T10 and rib 10 (detailed in Table 1). These landmarks were used to obtain the following measurements: the ribcage flare angle, the rib angle, and the maximum ribcage breadth, as defined below. The landmarks are located in Figure 1. The measurements are as follows:
  • The ribcage flare angle is defined as the angle between landmarks 5, 1, and 9. It is meant to represent the degree to which the ribcage “flares” at the bottom. Larger angles indicate a more flared lower ribcage;
  • The rib angle is defined as the angle between landmarks 2, 3, and 5 (right of rib 10). It is meant to represent the amount of space within the rib and the “openness” of the rib curvature;
  • The maximum ribcage breadth at rib 10 is defined as the distance between landmarks 4 and 8, which are the lateral-most points on the right and left of rib 10.
We also investigated the rib 10 shape to see whether it is related to the organ volume. Two landmarks and 18 semi-landmarks were also obtained for each side of rib 10 to obtain the rib curvature in the 3D Slicer. The two landmarks used were Landmark 2 and Landmark 5 and Landmark 6 and Landmark 9 for the right and left side, respectively. A total of 18 semi-landmarks were manually placed between these landmarks, along the curvature of the superior side of the rib shaft, and then resampled to achieve even spacing between the semi-landmarks. These 3D coordinates were used to perform analyses that assess the relationship between the rib 10 shape and the organ size.

2.3. Organ Volume Measurements

The size of the gut was quantified as the intestinal volume, which is the combined volume of the small and large intestines. Measuring the gut volume (GV) from the scans allowed for the in vivo measurement of the gut size, avoiding any changes that occur in the intestines after death or after being treated with formalin [41]. CT volumetry was used to measure the gut volume using the software Fiji (version 2.4.0), a distribution of ImageJ [42,43]. To measure the GV for one individual, it required the measurement of the surface area (cm2) of the organ by selecting the organ surface that appears on each CT slice, taking the sum of all the organ surface areas for all the slices, and then multiplying that figure by the thickness of the CT image slice (0.5 cm) to obtain a volume measurement (cm3) [30,44]. Muggli et al.’s method was used to obtain the liver volume [45], which required obtaining the maximum coronal width (CW), the anterior–posterior length (AP), and the superior–inferior (SI) length of the liver from the CT scans. The following equation was used (from Muggli and colleagues) to obtain the liver volume [46]: Liver Volume cm3 = CW × AP × SI × 0.31. The intraobserver error for the organ volume was calculated using the intraclass correlation coefficient (ICC), using the psych package in R [46,47]. The gut volume was measured by one observer (JU) and showed excellent intraobserver agreement (ICC = 0.94). The liver volume was also measured by one observer (VN) and showed good reliability (ICC = 0.89).

2.4. Statistical Analyses

All the statistical analyses were performed using R version 4.4.1 [48]. Multiple least squares regression was used, with body weight as a covariate, to test whether there were relationships between the organ volume and the following aspects:
  • The ribcage flare angle;
  • The rib angle;
  • The maximum ribcage breadth.
The observer error for all three variables showed excellent intraobserver agreement (ICC ≥ 0.93). Only one observer collected the landmarks and these variables (JU).
In both the liver and gut volume analyses, body weight was used as an independent or interacting covariate, depending on whether body weight affected the ribcage measurement. The ribcage breadth varies with weight and so weight was used as an interacting variable in the regression models (e.g., gut volume ~ breadth * weight). The rib angle and ribcage flare angle do not vary with weight, so weight was used as a non-interacting covariate in these regression models (e.g., gut volume ~ rib angle + weight). A relative weights analysis was performed afterwards to understand which independent variable (ribcage measurement or weight) affects the dependent variable (organ volume) the most, using the package relweights [49].
Lastly, to perform 3D geometric morphometric analyses of the rib 10 shape, we used the package geomorph [50,51]. After performing General Procrustes Analysis (GPA) to remove any variations unrelated to shape [52], we used the Procrustes-aligned shape coordinates to assess whether rib 10 is related to the gut volume and liver volume. To investigate the relationship between the organ volume and the rib 10 shape, we used a two-block partial least squares regression [53], one block being the shape data and the other block being the organ volume data.

3. Results

We found no significant associations between the liver size and any variable measured in terms of the female or male samples, when using weight as a covariate (Figure 2). We also found no relationship between the rib 10 shape and the liver or gut volume. Gut size was significantly associated with the rib angle and ribcage flare angle. A summary of the measurements of the samples can be found in Table 2. A summary of the results from all the regression models can be found in Table 3.
We found significant associations between the gut size and the ribcage flare, rib angle, and maximum ribcage breadth in both sexes (Figure 3), but the higher r2 values can be observed in the male sample. In male individuals, 53–55% of the gut volume variation can be explained by the ribcage variable and body weight. In female individuals, 24% of the gut volume can be explained by the ribcage flare, 15% of the gut volume variation can be explained by the rib angle, and 38% can be explained by the ribcage breadth (all with body weight as the covariate). These results are summarized in Table 3.
Upon further inspection using the relative weights analysis, we found that there are differences in how much the ribcage variable influences the gut volume relative to body weight. A summary of the relative weights analyses can be found in Table 4. While significant correlations between the gut volume and the rib angle (with weight as a covariate) were observed in both sexes, the relative weights analysis shows that most of this correlation is due to body weight (99% in the male sample and 97% in the female sample), rather than the rib angle.
Both the ribcage flare angle and the ribcage breadth influence the value of the correlation coefficients (r2) roughly as much, or more than, body weight in the regression models involving the female sample, compared to the regressions involving the male sample. The ribcage breadth contributes 65% to the r2 value, while body weight contributes the other 35% in the female regression model. In contrast, the ribcage breadth contributes only 15% to the r2 value in the male regression model, while body weight contributes 85%. The ribcage flare angle contributes 48% in the female regression model, compared to only 10% in the male regression model. These results may be interpreted as a sex difference in the gut–ribcage relationship, with body weight playing a lesser role in the gut size in female individuals. In both regression models, a larger flare angle (or the wider the ribcage “flares out” laterally, relative to the vertebral column) and a wider medio-lateral breadth is associated with a larger gut volume.

4. Discussion

4.1. Organ–Skeleton Relationships Are Complicated

The present study contributes to a more nuanced understanding of organ–torso relationships, through an examination of the ribcage’s association with two abdominal organs that it partially surrounds: the gut and the liver. These two organs have historically been used to understand the evolution of diet in hominins [1,2]; however, since organs are not preserved in the fossil record, the ribcage has been used as a proxy for the liver and gut size. Biological anthropologists have relied on qualitative observations of elements of the ribcage only to infer the organ size, speculating that a “flared” or “funnel-shaped” ribcage signals a large gut size and large liver size [1,2]. Organ–skeleton relationships are unfortunately understudied in biological anthropology and the ribcage has not been examined quantitatively in relation to the abdominal organs. Previous work on gut size and the pelvis has shown that the gut–pelvis relationship is more nuanced than previously thought, with sex differences in terms of the correlation between the gut volume and the pelvic canal [30,44]. The present study sought to examine whether the same can be said about the relationship of the liver and gut with the ribcage.
While gut size exhibited some significant associations with the ribcage, the liver size did not in both the male and female sample. Thus, we cannot infer the liver size from the ribcage flare, or breadth. Biological anthropologists should refrain from making assumptions about liver size using the skeleton only. It remains unclear as to why the liver is decoupled from the ribcage, but the gut is not. It is possible that the development of the lower ribcage is more integrated with the digestive system, compared to the liver [23].
Our results suggest that the relationship between the gut and the ribcage is different between the sexes, just like the relationship between the gut and the pelvis. The gut–ribcage relationship in the female torso seems to be weaker than the gut–ribcage relationship in the male torso, as shown by the smaller correlation coefficients in our regression analyses. From the results of the relative weights analyses, it also seems as though the gut–ribcage relationship seen in male torsos is driven by the relationship between the gut and body weight, while the gut–ribcage relationship seen in female torsos is driven by the relationship between the gut and the ribcage. Specifically, the ribcage flare and ribcage breadth show this pattern, but not the rib angle or rib shape.
Overall, these data support the speculation that a more “flared” ribcage does indicate a larger gut size, but the association between gut size and ribcage breadth or flare is not strong enough to confidently provide a quantitative estimate for the gut size from the ribcage. The r2 values for the male sample indicate that the weight and ribcage flare can only explain 54% of the variation in gut size while weight and ribcage breadth can explain about 53% of the variation in gut size (see Table 3 for details). In the female sample, it is less, where the weight and ribcage flare can explain only 24% of the gut size variation and the weight and ribcage breadth can explain 38% of the gut size variation.
The difference in the gut–ribcage relationship in male and female individuals in this study echoes the sex differences in the gut–pelvis relationship found in previous work by Uy and colleagues [30]. Specifically, they found that the gut size in female individuals was not associated with common pelvic dimensions, while the gut size in male individuals did have a small, but significant, association with the pelvic canal. Here, we found that the ribcage possibly also has a weaker relationship with gut size in female individuals. Although the pelvis and ribcage are morphologically integrated [54], it seems that the integration might serve a locomotor function [55] and that the abdominal viscera remain unaffected by the linkage. It is possible that this is related to the need for flexibility in terms of space within the female abdominal cavity, during pregnancy.

4.2. Implications for Paleoanthropology and Human Evolution

The weaker gut–torso relationship found in female individuals may indicate that the gut plays a role in allowing for the spatial accommodation of a gravid uterus. During gestation, the abdominal organs, particularly the intestines, are moved by the growing fetus; the spatial demands of pregnancy may be the reason for a greater degree of decoupling of the gut from the surrounding skeleton, in order to be more flexible.
Another pregnancy-related factor to consider is the difference in breathing mechanics between male and female individuals [33]. Female skeletons tend to possess more cylinder-shaped ribcages, while male skeletons have more pyramid-shaped ribcages [29]. Everyone uses both their diaphragm and the muscles between the ribs (intercostal muscles) to expand and contract the lungs when breathing. The wider, lower ribcage in male thoraces indicates a greater reliance on the diaphragm to breathe, while the wider, upper ribcage in female thoraces indicates a greater reliance on the intercostal muscles to breathe. In other words, people with broader lower ribcages (usually male individuals) tend to “belly breathe” with their diaphragm, to a larger extent. Due to the abdomen being full of the usual organs, plus an amniotic sac, placenta, and fetus during pregnancy, the abdomen cannot expand any more for “belly breathing”. Decreased abdominal compliance and upward displacement of the diaphragm in late gestation reduces the ability of the thoracic cavity to expand inferiorly into the abdomen when inhaling; instead, the lower thorax expands transversely and recruits the upper ribcage for further expansion [56,57]. Pregnant individuals must rely more on their ribcage for lung expansion, rather than relying on both the ribcage and the diaphragm, as they would when they are not pregnant. Perhaps the greater independence between the abdominal organs and the lower ribcage is a result of the reduced collaboration between the lower ribcage and abdominal expansion for breathing. The difference in the breathing mechanism, brought on by the difference in shape of the ribcage, may have prompted greater modularity between the ribcage and the abdominal cavity, especially in female bodies.
It is unclear when this would have evolved in the human lineage. It might also be the case that chimpanzees and other apes also exhibit this pattern, meaning it is not unique to humans and may have been present in our last common ancestor. Future research should inspect whether similar patterns of organ–skeleton relationships are present in chimpanzees and other non-human primates.
The evolution of the size of the abdominal organs, like the gut and liver, play an important role in understanding how the hominin diet evolved. In paleoanthropology, assuming the size of these organs using clues from the skeleton is common in the literature. However, we find that there is no straightforward relationship between soft tissue and hard bone. Little has been published showing that there is a quantitative relationship between abdominal organ size and the skeleton. The present study shows that there is no relationship between the lower ribcage and the liver size in humans, an assumption that has been made for Neandertals in the past. In regard to gut size, we cannot, with any certainty or nuance, infer the gut size using the ribcage. There seems to be a weaker relationship between the gut and the ribcage in female individuals. All these data suggest that paleoanthropology should be cautious in inferring the abdominal organ size, especially considering that sex can be a confounding factor.

Author Contributions

Conceptualization, J.U.; methodology, J.U.; formal analysis, J.U.; investigation, J.U., G.B. and V.N.; resources, J.U.; data curation, J.U., G.B. and V.N.; writing—original draft preparation, J.U.; writing—review and editing, J.U.; visualization, J.U. and G.B.; supervision, J.U.; project administration, J.U. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

This study used previously de-identified secondary data and did not require an IRB review.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data from this study (organ volumes and rib measurements) may be obtained here: https://doi.org/10.6084/m9.figshare.26940745.

Acknowledgments

The authors are thankful for the feedback provided by individuals from the American Association of Biological Anthropologists Annual Meeting in 2023, where an earlier version of this work was presented as a poster.

Conflicts of Interest

The authors declare that there are no conflicts of interest.

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Humans 04 00020 g001
Figure 1. Landmarks used to obtain linear measurements and angles. Descriptions can be found in Table 1. This image includes ribs 9–12. The landmarks are placed on rib 10 and T10.
Figure 1. Landmarks used to obtain linear measurements and angles. Descriptions can be found in Table 1. This image includes ribs 9–12. The landmarks are placed on rib 10 and T10.
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Figure 2. Ordinary linear regression graphs showing the liver volume’s relationship with the ribcage flare angle (left) and the rib angle (right). There are no significant correlations between the liver volume and the ribcage flare or the rib angle in either sex.
Figure 2. Ordinary linear regression graphs showing the liver volume’s relationship with the ribcage flare angle (left) and the rib angle (right). There are no significant correlations between the liver volume and the ribcage flare or the rib angle in either sex.
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Figure 3. Simple linear regressions showing the gut volume’s relationship with the ribcage flare angle (left) and the maximum ribcage breadth (right). Both male and female samples had significant associations in terms of the flare and breadth (with weight as a covariate in the analysis), but there are differences in the strength of these associations, with male regression having higher r2 values than the female regression.
Figure 3. Simple linear regressions showing the gut volume’s relationship with the ribcage flare angle (left) and the maximum ribcage breadth (right). Both male and female samples had significant associations in terms of the flare and breadth (with weight as a covariate in the analysis), but there are differences in the strength of these associations, with male regression having higher r2 values than the female regression.
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Table 1. Landmark descriptions.
Table 1. Landmark descriptions.
LandmarksDescription
1Anterior–superior most point on the T10 vertebral body
2Anterior-most point on the head of rib 10 on the right side
3Most superior point of the rib angle on the posterior side of rib 10 on the right side
4Lateral-most point on the shaft of rib 10 on the right side
5Medial-most point on the sternal end of rib 10 on the right side
6–9Repeat of landmarks 2–5, but on the left side
Table 2. Sample mean and standard deviation (mean ± SD).
Table 2. Sample mean and standard deviation (mean ± SD).
MeasurementFemale (N = 31)Male (N = 30)
Liver Volume (cm3)1559 ± 3941604 ± 392
Gut Volume (cm3)4367 ± 9055742 ± 1525
Ribcage Flare Angle113° ± 10123° ± 11
Rib Angle93° ± 591° ± 5
Max Breadth (cm)26 ± 229 ± 2
Table 3. Results of the regression analyses performed for the organ volume and rib 10.
Table 3. Results of the regression analyses performed for the organ volume and rib 10.
Regression Modelsr2 (p-Value) Female Sampler2 (p-Value) Male Sample
Liver ~ Ribcage Flare + Wt0.03 (ns)0.04 (ns)
Liver ~ Rib Angle + Wt0.01 (ns)0.03 (ns)
Liver ~ Ribcage Breadth * Wt−0.02 (ns)0.06 (ns)
Liver ~ Rib 10 Shape0.44 (ns)0.24 (ns)
Gut ~ Ribcage Flare + Wt0.24 * (p < 0.01)0.54 * (p < 0.01)
Gut ~ Rib Angle + Wt0.15 (p = 0.04)0.55 * (p < 0.01)
Gut ~ Ribcage Breadth * Wt0.38 * (p < 0.01)0.53 * (p < 0.01)
Gut ~ Rib 10 Shape0.61 (ns)0.20 (ns)
First column indicates dependent and independent variables used; body weight was used as a covariate. Moreover, r2 indicates the proportion of organ volume that is explained by the ribcage variables and weight. Significant p-values are indicated by bold numbers (p < 0.05); those with an asterisk * indicate a p-value of less than 0.01. ns = not significant.
Table 4. Results of the relative weights analyses from multiple regression models, with p < 0.01. The relative contributions of body weight and the ribcage measurement towards the r2 of the models are shown for the male and female samples.
Table 4. Results of the relative weights analyses from multiple regression models, with p < 0.01. The relative contributions of body weight and the ribcage measurement towards the r2 of the models are shown for the male and female samples.
Regression Models *Female SampleMale Sample
Gut ~ Ribcage Flare48% rib < 52% weight10% rib < 90% weight
Gut ~ Rib Angle3% rib < 97% weight1% rib < 99% weight
Gut ~ Ribcage Breadth65% rib > 35% weight16% rib < 84% weight
* For all regressions, body weight was used as a covariate.
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Uy, J.; Beresnevičiūtė, G.; Nguyen, V. The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology. Humans 2024, 4, 310-320. https://doi.org/10.3390/humans4040020

AMA Style

Uy J, Beresnevičiūtė G, Nguyen V. The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology. Humans. 2024; 4(4):310-320. https://doi.org/10.3390/humans4040020

Chicago/Turabian Style

Uy, Jeanelle, Gabrielė Beresnevičiūtė, and Vyvy Nguyen. 2024. "The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology" Humans 4, no. 4: 310-320. https://doi.org/10.3390/humans4040020

APA Style

Uy, J., Beresnevičiūtė, G., & Nguyen, V. (2024). The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology. Humans, 4(4), 310-320. https://doi.org/10.3390/humans4040020

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