DIAGNÒSTICO ACTUAL DE LA ENSEÑANZA EN LA CÁTEDRA DE

Analysis 3.1 determined sexual dimorphism in the size of the adult facial skeleton of each species by means of t-tests. The results of this analysis for each species are displayed in Table 3.1. In each case an F- test was performed first, in order to determine the equality or inequality of the variance for each sex, and then a parametric or non-parametric t-test, respectively, was selected for each species. Both G. gorilla and P.

troglodytes have unequal male and female variances for centroid size, both species' t-tests are also highly significant. Male and female adult P.

paniscus, however, have equal size variances for centroid size of the facial skeleton and based on the t-test there is an insignificant difference between the sex mean sizes.

Analysis 3.2 examined the significance of sexual dimorphism in the shape of the adult facial skeleton of each species based on the statistical significance of the Procrustes distance between the adult male mean shape and adult female mean shape of each species. The Procrustes distances and p-values are presented in Table 3.2. The Procrustes distances between the sex mean shapes are highly significant for both G.

gorilla and P. troglodytes. However the distance between the P. paniscus

mean male and mean female shapes is highly insignificant, indicating that they are statistically indistinguishable.

Analysis 3.3 explored the pattern of variation between adult male and female shape means of the sexually dimorphic species. Since Analysis 3.2 indicated that the facial skeleton of P. paniscus is not sexually dimorphic, this analysis was carried out on just G. gorilla and P.

troglodytes. PCI accounts for 84.6%, PC2 for 12.8% and PC3 for 2.5% of the variance amongst the means. The remaining PC, PC4 only accounts for <0.1% of the variance. The PCs are shown in Figure 3.1 and Figure 3.2. PCI clearly accounts for a large proportion of the interspecific differences regardless of sex, however the polarity of the male and

female of both species is consistent on this PC. There is a considerable overlap of the two species on PC2, with G. gorilla having a greater spread than P. troglodytes, and again the polarity of the males and females is consistent. When the PC scores of the mean shapes are compared across PC1 and PC2 together the overall pattern is remarkably similar, such that the vectors connecting the male and female of each species are parallel (these vectors are represented by dashed lines in Figures 3.1 and 3.2, and are free hand representations). Therefore on these first two PCs, apart from the interspecific separation on PCI, the differences in direction between the intersex vectors of the two species are small. PC3 (Figure 3.2) however, although only accounting for 2.5% of the total shape variance amongst means, shows a complete reversal in the sex polarities between G. gorilla and P. troglodytes. The differences between sexes in PC3 scores are very similar for both species. PC4 is not graphically represented due to its small contribution to the total variance (<0.1 %).

Analysis 3.4 visualises the pattern of shape variation among the adult sex means determined in Analysis 3.3. The shared aspects of sexual shape dimorphism represented by PCs 1 and 2 are visualised in Figures 3.1a and 3.1b. Figures 3.1a and 3.1b show the mean shape warped along an axis (represented as the double headed arrow in Figure 3.1), that approximates the mean intersex vector. Figures 3.1a and 3.1b are respectively the mean shape warped (along the arrow) between PC2 = -0.06 and PC2 = 0.06. The shape difference between the warped means are highlighted by the use of (TPS) Cartesian transformation grids, where the reference shape is the female extreme (Figure 3.1a) and the target shape is the male extreme (Figure 3.1b).

The transformation grids in Figures 3.1a and 3.1b essentially show a relative decrease in the width of the palate and a relative increase in the width of the zygomatic region of the face in the males (anterior view of Figure 3.1b). In particular, the anterior view of Figure 3.1b shows a lateral increase relative to the superoinferior dimension. The midface is relatively expanded mediolaterally in the region lateral to the infraorbital foramen

and zygomaticomaxillary suture. This is accentuated by a relative mediolateral decrease in the alveolar/palatal region, which can be clearly seen from the palatal view of Figure 3.1b, although the grid is not positioned to show this shape difference. The grid however, in the palatal view (Figure 3.1b) is evidently distorted in the region of the canine, showing a relative increase in the male means.

The visualisations in Figure 3.2 show the mean shape warped along the extrapolated intersex vectors for the adult sex means of G.

gorilla and P. troglodytes on PCI and PC3 combined (approximated by dashed lines on the graph). Therefore, as with Figure 3.1a and Figure 3.1b, the visualisations in Figure 3.2 also describe shape variation along P C I. Figure 3.2a shows the mean shape warped to the point at which the two vectors, extrapolated beyond the negative extreme of PC3, intersect each other. In both cases this covers a distance that is approximately three times the length of the vectors themselves, as before this exaggerates the shapes thus making the shape differences more obvious. Figures 3.2b and 3.2c show the mean shape warped along the intersex vectors of G. gorilla and P. troglodytes respectively, beyond the positive extreme on PC3, again by a factor of three for clarity. Thus Figure 3.2a is the reference shape and represents an exaggeration of both the mean female G. gorilla shape and the mean male P. troglodytes

shape on PCI and PC3, whereas Figures 3.2b and 3.2c represent the exaggerated shapes of the mean male G. gorilla and the mean female P.

troglodytes, respectively.

The shape difference between the G. gorilla mean male and female shape can be interpreted from the transformation grids in Figure 3.2b. Viewed laterally, the mean male has a decrease in the superoinferior dimension relative to the female, with localised relative anteroposterior expansion, particularly in the superior nasal area anterior to the orbital margin and the lateral region of the orbital margin. The relative mediolateral compression of the mean male palate can be easily interpreted from the grid in the palatal view of Figure 3.2b.

The P. troglodytes transformation grids in Figure 3.2c represent in the reverse ordering of sexes to that in Figure 3.2b, in this case the reference (Figure 3.2a) represents the mean adult male shape and the target (Figure 3.2c) represents the mean adult female shape, reflecting the polarity reversal of the sexes of each species on PC3. Compared to the representation of the male P. troglodytes shape on PC1 and PC3 (Figure 3.2a), the female has a relative anteroposterior compression in the midface. There is also a shift in the proportional bony contributions to the infraorbital and malar regions, whereby the female has a reduced maxillary contribution and concomitant increase in the zygomatic contribution to the inferior margin of the orbit.

Analysis 3.5 ascertained the significance of the difference between the intersex vectors of Analysis 3.2. In the PCA in Figure 3.3, PC1 completely separates the distribution of bootstrapped intersex vectors between the species such that there is no overlap and the true intersex vectors of each species is within its respective species distribution. Thus there is very strong evidence from this analysis that the intersex vectors differ significantly between G. gorilla and P. troglodytes. Note that the larger scatter of intersex vectors in P. troglodytes compared to that within G. gorilla indicates the relatively greater uncertainty in estimating this vector in the former because of the lesser magnitude of shape sexual dimorphism (as determined in Analysis 3.2). Formal statistical testing of significance is not a straightforward matter and thus is the subject of ongoing research by statisticians (Dryden, pers. comm.).

3.3.2 ONTOGENETIC BASIS OF SEXUAL DIMORPHISM IN THE