Chapter 8: What It Means to be a Hominin

Question 1

encephalized

Answer 1

“encephalization” refers to the ratio of brain size to body size; the higher this ratio for a given species, the more encephalized it is said to be

Question 2

obligate bipeds

Answer 2

in biology, “obligate” denotes a condition of necessity; being a “biped” refers to the condition of walking on two legs; therefore, obligate bipeds walk on only two legs

Question 3

conditio sine qua non

Answer 3

a Latin term meaning “without which there is nothing.” In this context, large brains were once thought to be the preeminent hominin feature from which all else followed. We know now that this is not the case.

Question 4

facultative bipedalism

Answer 4

adopting a two-legged posture only under particular circumstances as an exception to a habitual non-bipedal form of locomotion

Question 5

orthograde

Answer 5

indicating upright or erect posture, notably with regard to the trunk

Question 6

tripedalism

Answer 6

a theoretical model proposing that early Miocene hominins may have adopted a three-limbed gait prior to bipedalism, in order to carry objects such as stones

Question 7

selective differential

Answer 7

a measure of the probability that a given phenotype will reproduce compared to an alternative phenotype

Question 8

energetic efficiency

Answer 8

the assessment of the relative metabolic cost of performing a given task

Question 9

convective cooling

Answer 9

reduction of body temperature by air movement facilitating heat loss through evaporation of sweat

Question 10

obstetric dilemma (OD)

Answer 10

the hypothesis that evolution of larger brains competed with narrowing of pelvic structure associated with adopting a bipedal gait, resulting in babies being born in a more helpless stage of development

Question 11

altriciality

Answer 11

a state at birth in which the newborn lacks the ability to provide for itself and receives food and care from its mother or other caregiver

Question 12

energetics of gestation and growth (EGG)

Answer 12

the hypothesis that the evolution of larger brain size required babies to be born at an earlier stage of fetal development due to the increasing cost of gestation for the mother; in effect, it requires less energy to feed a newborn infant than to prolong gestation

Question 13

basal metabolic rate

Answer 13

the amount of energy needed to sustain organ function while at rest and without needing to produce or lose body heat

Question 14

last common ancestor (LCA)

Answer 14

a term designating that species from which diverging clades evolved

Question 15

pronograde

Answer 15

a posture in which the trunk is held more or less horizontal and approximately parallel with the surface on which the animal moves

Question 16

orthograde clamber

Answer 16

a form of arboreal hand-assisted bipedal locomotion applied specifically to orangutans, involving extension at the knee, hip, and shoulder

Question 17

home base

Answer 17

an area likely associated with shelter and water to which hominins would repeatedly return from foraging

Question 18

concealed ovulation

Answer 18

ovulation occurs during that stage in a placental female mammal’s reproductive cycle (estrus) during which is she receptive to sexual intercourse (either physiologically or induced through copulation); it may be signalled with swelling and reddening of the genital area, or through chemical means such as pheromones. Thus, concealed ovulation refers to the absence of signalling, such that the male is unable to detect when a female may be likely to conceive. Some recent evidence suggests that chemical signalling still occurs between human females and males.

Question 19

birth spacing

Answer 19

the amount of time that passes between life births, e.g., birthdate to birthdate. In primate life history, birth spacing is correlated with a number of variables, including female rank, and access to food resources is a primary determinant of birth spacing

Question 20

androcentric

Answer 20

male-centred; the corresponding term for female-centred arguments is gynocentrism

Question 21

time allocation

Answer 21

in the study of life history, time allocation studies document how much time is spent during a given time period (day, season, age stage, etc.) performing particular tasks

Question 22

energy budget

Answer 22

a compendium of the sources and expenditures of energy, typically measured in calories or kilojoules

Question 23

endurance running

Answer 23

the idea that our ancestors evolved the capability for long distance, metabolically efficient running as a unique aspect of human bipedal locomotion

Question 24

aerobic metabolism

Answer 24

the conversion of glucose to energy within mitochondria in the presence of oxygen, from sources such as carbohydrates, fatty acids, and amino acids

Question 25

cursorial

Answer 25

pertaining to animals adapted for efficient running

Question 26

occlusal plane

Answer 26

the occlusal plane refers to the orientation of the chewing (i.e., occlusal) surfaces of the upper and lower dentitions

Question 27

diastema

Answer 27

a space between adjacent teeth in the dental row into which the protruding canine from the opposite jaw fits in a closed mouth, found in nonhuman primates and some early hominins

Question 28

distolingual

Answer 28

the conjuction of the rearward (distal, away from the midline of the mouth) and inner (lingual, or tongue-facing) surfaces of a tooth

Question 29

mesiobuccal

Answer 29

the conjunction of the forward (mesial, toward the midline) and buccal (outer, cheek-facing) surfaces of a tooth

Question 30

canine honing

Answer 30

sharpening, in this instance of one tooth, the upper canine, through repeated contact with another tooth, the lower third premolar

Question 31

sectorial P3

Answer 31

in Old World primates, a lower third premolar in which the mesiobuccal surface appears as a long, sloping surface due to contact with the upper canine

Question 32

intrasexual

Answer 32

“intra” means within; thus intrasexual variation refers to differences that exist within males or females separately

Question 33

correlated response

Answer 33

changes that occur in one feature are consistently associated with changes occurring in another

Question 34

prognathism

Answer 34

projection of the lower face; the gnathic portion of the face contains the upper and lower jaws

Question 35

microstructure

Answer 35

the arrangement of cells and their associated structures that contribute to the material properties of a tissue; usually, microstructure is viewable only with the use of instruments such as microscopes and microCT scanners

Question 36

relative brain size

Answer 36

the absolute size of the brain adjusted to reflect the absolute size of the body of which it is a part, since we expect a larger body to have a proportionately larger brain. Primates tend to have larger brains for a given body size than other mammals

Question 37

scaling

Answer 37

in biology, refers to the pattern of change of a part in relation to a whole; may be isometric (a unit of change in body size is matched by a unit of change in the part) or allometric (the change in a apart is greater or less than the change in the whole)

Question 38

endocasts

Answer 38

impressions of the inner surface of the cranium and outer surface of the brain, which may occur naturally as “fossils” or from moulds created in the laboratory

Question 39

paleoneurology

Answer 39

the study of the evolution of the brain and its functions

Question 40

lunate sulcus (LS)

Answer 40

a fissure found in the anterior portion of the occipital lobe that demarcates the primary visual cortex; readily visible in nonhuman primate brains, the LS is often not seen in humans