modern variation and evolutionary change in the hominin eye orbit

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1.2 Evolution of the hominin brain, neurocranium, and faceIncreased brain size in hominins has contributed to a number of changes in otherfeatures of the neurocranium and face, and is thought to have modified the size andlocation of various traits while also impacting the functional efficiency of mastication andolfaction (Lieberman, Ross, Ravosa, 2000; Ravosa et al. 2000; Ross, 1995). The brain isimmense in humans and has expanded considerably during the last 2 million years,though enlargement of the various structures that make up the brain have not increasedisometrically during hominin evolution (Rilling, 2006).The neocortex is greatly expanded in primates relative to most other mammals, somuch in fact that it accounts for 80% of total brain mass in anthropoids (Aiello & Dean,1990; Kornack & Rakic, 2001). During human evolution the neocortex has grown tooccupy an even larger share of the brain, with a disproportionate enlargement of thetemporal and prefrontal association cortices, an increase in connectivity within andamong cerebral cortical association areas involved in cognition, as well as an increasedgyrification of the cortical surface (Rilling, 2006). This gyrification has primarilyoccurred in the prefrontal cortex and is the result of bending and folding of this outermostlayer as it scales with positive allometry on brain volume within the confines of aspherically shaped skull (Rilling, 2006).The frontal lobes of the neocortex have expanded considerably during humanevolution and have been widely studied as a result of their assumed role in languagedevelopment and higher cognition (Wu et al. 2007). In early hominins the fontal lobesare relatively flat and narrow, but have become taller, wider, and more rounded over thecourse of human evolution (Bruner, 2003). This area of the brain has expanded to the3
extent that in modern humans it sits directly over the eyes and has filled in the spacepreviously occupied by the brow ridge in ancestors of modern humans (Moss & Young,1960). This cerebral expansion, and in particular a more anterior position of the frontallobes, has repositioned the brain atop the eyes and created a situation in which twodifferent functional systems (the eyes and brain) both make use of the frontal bone.Marked encephalization throughout hominin evolution is therefore expected to influencethe relative size and position of these two features, possibly resulting in decreasedfunction of the visual system.In chapter 4 of this thesis, relationships among the cranium, orbits, and lower faceare investigated in the context of hominin evolutionary trends of increased cranial sizeand decreased facial prognathism. It is proposed that orbital morphology varies inpredictable ways in relation to these long-term craniofacial changes, which have resultedin a number of unique characteristics of the skull in modern humans. The results of thisanalysis and those from chapter 5, which investigates more recent evolutionary changesin orbital morphology since the Upper Paleolithic in Western Europe, will be assessed inthe context of how the eye and surrounding soft tissue may be impacted by temporalmodification to the bony orbit that circumscribes this functional system.1.3 Structural and functional components of the skullMost changes in craniofacial form during ontogeny and throughout homininevolution are best explained in the context of functional craniology, which is an approachto understanding the skull as a matrix of hard and soft tissues arranged in a physicalnetwork, in which the final form is a product of forces and constraints among these4
Page 1: MODERN VARIATION AND EVOLUTIONARY C
Page 7 and 8: VITAJanuary 2, 1978……………
Page 9 and 10: TABLE OF CONTENTSPageAbstract .….
Page 11 and 12: 7. Summary and Conclusion………
Page 13 and 14: Table 3.13: Wilks' lambda and Chi-s
Page 15 and 16: Figure 5.4: Change in orbital bread
Page 17: Although there is a great deal of c
Page 21 and 22: in the face and cranium” (Enlow &
Page 23 and 24: etween the neurocranium and face, u
Page 25 and 26: Schultz (1940) observes a negative
Page 27 and 28: sphenoid, and between 5 and 6 in th
Page 29 and 30: its relative position during forwar
Page 31 and 32: fact more variation exist between r
Page 33 and 34: plane is highly related to factors
Page 35 and 36: cranial and facial height occurs in
Page 37 and 38: assessed in relation to patterns of
Page 39 and 40: or throughout hominin evolution cou
Page 41 and 42: in roughly the same proportions (An
Page 43 and 44: association with juvenile-onset myo
Page 45 and 46: Craniofacial Variables Label Landma
Page 47 and 48: In this investigation the FH is not
Page 49 and 50: this study most research questions
Page 51 and 52: Craniofacial Variables Label ErrorC
Page 53 and 54: CHAPTER 3MODERN HUMAN VARIATION IN
Page 55 and 56: Sample Sample Size RepositoryAfrica
Page 57 and 58: change in orbital anatomy and will
Page 59 and 60: 3.3.1 Interorbital breadth and bior
Page 61 and 62: 3.3.2 Orbital height and orbital br
Page 63 and 64: Basion-Superior Orbit, Basion-Infer
Page 65 and 66: 98Vertical Angle of Orbital Margins
Page 67 and 68: statistical tools. In the next sect
Page 69 and 70:
Correlation obbobhobdobvobfekbdkbbs
Page 71 and 72:
obbobhobdobvobfekbdkbbsobioFunction
Page 73 and 74:
variables in the first discriminant
Page 75 and 76:
distance matrix, which shows the Af
Page 77 and 78:
golxcbzybbbhbplufbnphnlhobbobhobdob
Page 79 and 80:
non-orbital cranial and facial trai
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Function 242012AncestryAfricanAsian
Page 83 and 84:
eadth (ekb), and basion-orbitale (b
Page 85 and 86:
CHAPTER 4EVOLUTIONARY CHANGE IN THE
Page 87 and 88:
This sample represents the most mor
Page 89 and 90:
analysis. This was done to remove a
Page 91 and 92:
190Boxplot of Cranial Size vs Time1
Page 93 and 94:
flexed in association with neurocra
Page 95 and 96:
Variables N Coefficient t p R²1) B
Page 97 and 98:
Ross (1995) also finds a relationsh
Page 99 and 100:
Figure 4.4: Image of Shandingdong (
Page 101 and 102:
CHAPTER 5EVOLUTIONARY CHANGE IN THE
Page 103 and 104:
ecause of a general reduction in cr
Page 105 and 106:
adequate space within the orbits fo
Page 107 and 108:
Western European temporal groups sa
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Upper Paleolithic (Figure 5.4). The
Page 111 and 112:
Regardless of the relative contribu
Page 113 and 114:
of facial projection vs. time indic
Page 115 and 116:
Boxplot of Cranial Index vs Time908
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5.6 Results of regression analyses:
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Although the direction and magnitud
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Additionally, because the eyeball s
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corroborates the findings of other
Page 125 and 126:
Sample Sample Sizes Method DataFema
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approximately 3.5 show little to no
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In females there is a clear differe
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Boxplot of Orbital Vol vs Sex25.022
Page 133 and 134:
Ancestral Group N mean s.d. t pAfri
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5.5Boxplot of Relative Eye Size vs
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away from emmetropia in individuals
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ceases. Additionally, different pat
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of the orbit that the eyeball fills
Page 143 and 144:
CHAPTER 7SUMMARY AND CONCLUSION7.1
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margins in this group. The slightly
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classification of dry skulls and as
Page 149 and 150:
Six orbital variables were used to
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A final prediction relating to how
Page 153 and 154:
Nevertheless, orbital traits that c
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etraction could not be evaluated. H
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A statistically significant negativ
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to engage in non-subsistence activi
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comes at a cost to visual acuity ho
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trajectories between the eye and or
Page 165 and 166:
BIBLIOGRAPHYAiello, L., Dean, C. (1
Page 167 and 168:
Bruner, E., Saracino, B., Passarell
Page 169 and 170:
Goldschmidt, E., Lam, C., Opper, S.
Page 171 and 172:
Lam, C., Edwards, M., Millodot, M.,
Page 173 and 174:
Quant, J., Woo, G. (1992) Normal va
Page 175:
Weiss, K. (2002) How the Eye Got it
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modern variation and evolutionary change in the hominin eye orbit

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