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The selection pressure to shift to a high-quality, more animal-based,

energy-dense diet may have involved the increase in brain size, as explained by the

expensive tissue hypothesis (Aiello and Wheeler 1995 ; Armelogos 2010 , 2014 ;

Leonard et al. 2003 ). Larger brains imply an increased capacity to develop more

efficient forging strategies resulting in the preferential selection of energy and

nutrient-dense foods to offset the additional energy cost of a metabolically active

brain (Power and Schulkin 2009 ; Armelogos 2010 , 2014 ).

The third trend is the reduction in the size of the jaws and teeth, particularly the

premolars and molars, a concomitant reduction in the masticatory muscles and a

remodeling of the skull reducing bony eminences in response to dietary changes

and food processing, including cooking techniques (Armelogos 2010 , 2014 ;

McHenry and Coffing 2000 ; Wrangham 2009 ). The fourth trend is the decrease in

size of the large intestine and the lengthening of the small intestine facilitating the

digestion and absorption of fats, amino acids, and simple sugars of relatively lower

fiber diets compared to very highfiber diets of non-hominid primates that require

greater processing, including fermentation offiber, in the large intestine (Armelagos

2014 ; Milton 2003 ).
Armelagos ( 2010 , 2014 ) argues that omnivory, that is, dietaryflexibility, was

and is a key factor in human consumption patterns. Humans have a psychophysi-

ological motivation for dietary variety (neophilia) and are, yet, cautious about

deleterious, possibly poisonous, items (neophobia). The innate liking of

sweet-tasting foods and rejection of bitter-tastingflavors increase ingestion of

energy-dense sugary and starchy foods and the rejection of potentially toxic foods

(Macbeth and Lowry 1997 ). Furthermore, sensory-specific satiety, or palate fatigue,

describes reduced interest in a food after consumption and encourages food variety.

Table 10.1 Generalized hominin body and brain size trends

Taxa/grades Dates

(mya/kya)a

Stature

(m)b

Body

massb(kg)

Brain sizeb

(cc)

Encephalization

quotient (EQ)b,c

Australopithecines 4.2–2.2 1.05–151 29– 45 360 – 545 2.5–2.7

Paranthropines 2.3–1.4 1.10–1.37 32– 49 410 – 530 2.7–3.0

Homo habilis 2.4–1.6 1.00–1.60 32– 37 600 – 800 3.4–3.6

Homo

erectus/Homo

ergaster

1.9– 200

kya

1.60–1.85 52– 66 900 – 1250 3.3–3.6

Neanderthals 300 – 30 kya 1.52–1.68 52– 70 1450 – 1620 5.4–5.5

AncientHomo

sapiens

100 – 1900

kya

1.58–1.70 50– 65 1200 – 1600 5.3–5.8

ModernHomo

sapiens

Today 1.61–1.75 74– 86 1200 – 1600 5.3–5.8

McHenry and Coffing ( 2000 )
Power and Schulkin ( 2009 )
Ruff et al. ( 1997 )
amyaMillions of years ago,kyathousands of years ago
bStature, body mass, brain size, and EQ are inclusive of females and males
cEncephalization quotient = brain mass (g)/11.2×body mass0.76

198 L.S. Lieberman