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Chapter 7

ANT203H5 Chapter Notes - Chapter 7: Canine Tooth, Zygote, Incisor

Course Code
Esteban Parra

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Notes From Reading
Characteristics of Living Humans
Distribution and Environment
-Humans are the most widely distributed living primate species
-During the course of human evolution, we have expanded into many different
-Biological adaptations have aided humans in new environments (such as cold weather,
high altitudes)
-Cultural adaptations of humans have allowed greater expansion
oEnabled us to range far beyond our biological limitations
oPermitted incredible population growth
Brain Size and Structure
-Ape’s skull is characterized by a relatively small brain and large face, modern humans
have relatively large brains and small faces
-The relationship between brain and body size is not linear
oAs body size increases, brain size increase – but not at the same rate
oAllometry – the study of the change in proportion of various body parts as a
consequence of different growth rates
-Allometric relationship between brain size and body size is quite regular among almost
all primates (most notable exception is humans)
oThe human brain has a higher proportion of neocortex (part of the cerebral
cortex), involved in conscious thought and language
-The human brain is not only larger than the brain of a chimpanzee, but also structurally
-The increased convolution of the human cerebral cortex (the folding of brain tissue)
means that the brain of a human child with the same volume of a chimpanzee has more
cerebral cortex
-Bipedal – Moving about on two legs. Unlike the movement of other bipedal animals,
such as kangaroos, human bipedalism is further characterized by a striding motion
-The physical structure of human beings shows adaptation for upright walking as the
normal mode of movement
oApes can walk on two legs, however they cannot as well or not as often
-Humans bipedalism is made possible by anatomical changes involving the toes, legs,
spine, pelvis, and various muscles
-No bones are added or deleted; the same bones can be found in humans and in apes
oThe changes involve shape, positioning, and function
-Chimps have a divergent big toe which allows them to grasp with their feet, where the
big toe of the human is tucked in next to the other toes
-Humans are literally “knock-kneed” where the femurs are sloped inward from the hips
which transmits our weight directly underneath us
oIn contrast, the angle of an ape femur is very slight, where the ape is off balance
and tends to fall toward one side
-Human spine also promotes balance when we walk upright
oSpinal column of humans is vertical, allowing weight to be transmitted down
through the center of the body
oIn knuckle-walking apes, the spine is bent in an arc so that when the apes stand
on two legs, the center of gravity is shifted to the front of the body
-Human pelvis is shaped differently from an ape pelvis as well

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Notes From Reading
oIt is shorter top to bottom and wider side to side, providing changes in muscle
attachment that permit striding bipedalism
oShortness of the human pelvis allows greater stability when we stand upright
Canine Teeth
-Human canines are small and do not project beyond the level of the other teeth
-Human canine teeth serve much the same function as the incisor teeth
-Given that canine teeth serve as weapons in many primate species, the lack of large
canine teeth in humans seems to imply that we do not need them for weapons anymore
Genetic Differences between Humans and Apes
-Humans and chimpanzees share over 98 percent of their DNA sequences
-The FOXP2 gene, located on human chromosome 7, which may have something to do
with the evolution of human language
oA rare mutant allele of this gene is associated with language impairment, and two
copies of the nonmutant functional form of FOXP2 are needed for normal
language acquisition
oSame form of this gene is found in chimpanzees, gorillas, and rhesus monkeys,
all of which differ from human by two amino acid substitutions
oThis pattern that suggests that these two changes occurred after the hominin line
split from the common ancestor with African apes
-Some specific human traits have been traced to the loss of regulatory genes during human
evolution examined the genomes of humans, chimpanzees, and macaques (an Old World
monkey) and identified 510 DNA sequences that had been present in chimpanzees but
were lost during the course of human evolution
oOne sequence acts to regulate a gene that limits tissue growth, and the deletion of
this regulatory sequence in humans may be associated with the expansion of the
cerebral cortex, possibly representing a genetic mechanism associated with the
rapid brain growth seen in human evolution
oThe other sequence affects an androgen receptor; the deletion of the regulatory
gene in humans is associated with the loss of sensory whiskers and penile spines,
both of which are absent in humans but present in many other mammals
-Apes have large jaws and powerful jaw muscles for chewing
oLiving humans have rather small, less powerful jaws
Sex and Reproduction
-The fact hat humans do not have the estrus cycle has often been cited as a unique aspect
of human sexuality
oEsctrus – A time during the month when females are sexually receptive
-For the most part, temperate-zone domestic animals breed only during certain seasons
and mate around the time of ovulation
oHuman females, in contrast, cycle throughout the year and may mate at any time
during the cycle
oThe human pattern of reproduction is basically the same as that of most other
primates: single births
-The pelvic anatomy of living humans means that a new baby has to rotate through a
narrow and twisting birth canal
oChildbirth in humans is more difficult and more complicated than in apes, due to
our enlarged brains and the changes in pelvic anatomy that accompanied
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