ANTC16 Lecture 10
Adaptation is a feature of an organism that increases the likelihood of its survival and reproduction in a
particular environment. For example the arctic hare has white fur while the desert hare has brown fur, the fur
colour helps them camouflage in their environment. The arctic hare has short ears and short limbs which are
good at keeping heat while the desert hare has long ears and limbs which are good at losing heat, these are
adaptive traits to their climate.
Natural selection: differential survival and reproduction of particular variants within a species, leading to
change in which some variants in the population become more common, and others less
Directional selection: one part of a range of variation of a species
is better adapted
In subsequent generations the whole population will shift to be
more like that part because of differential survival and
In this example the hairy cacti are more successful
Directional selection takes place
The population is make up hairier cacti (in subsequent generations)
Some forces thought to have shaped modern human variation through adaptation include altitude, diet, and
There are many challenges that people at high altitudes face, such as increased radiation, colder temperatures,
stronger winds, shorter growing season, and lower partial pressure of oxygen.
ANTC16 Lecture 10
The graph on the left plots barometric pressure in relation to arterial blood saturation %/partial pressure of
oxygen. We can see that as barometric pressure increases the partial pressure of oxygen decreases. At about
3000 meters above sea level humans begin to show a serious handicap in their ability to get enough oxygen. If
populations live above 3000 meters they are considered high altitude populations.
Relationship between body mass and altitude was studied in South American populations (Peru). The relation of
mean body mass between highlanders and lowlanders in both sexes is illustrated on the graph on the right. The
graph shows that in both males and females highlanders (those that live in high altitudes) tend to have lower
stature than lowlanders (those that live at low altitudes).
Atacama highlanders (Chile)have unusually broad chests, which is likely to be associated with high altitudes.
This body shape/type can improve oxygen intake (in oxygen deficient environments).
Genetic signal associated with population differences in genes that are related to factors, which are thought to
be adaptive such as altitude. The genetic differences were studied by comparing the genetic material of Han
(chinese) populations and Tibet populations. The graph is a distribution map of SNAPS. The graph shows a one
to one relation between the Han and Tibet populations. However EPAS1 is found in low frequencies in Han
populations but high frequencies in Tibet populations. ESPAS1 gene is associated with oxygen sensing. There is
a 78% frequency difference, which suggests that it took about 4000 years for 90% of Tibetan population to have
this gene. This is one of the fastest hypothesized cases of natural selection.
Another factor that is thought to have shaped modern human variation is diet.
Biocultural evolution: The choices that populations have made about the type of diet they eat has
shaped/influenced their evolution. ANTC16 Lecture 10
Most mammals can’t drink milk. They lose their ability to digest milk because they lose the gene that produces
the enzyme (lactase), which is used to digest the sugar in milk (lactose), this mechanism turns off once the
animal is weaned.
People have adapted to drinking milk – usually in populations that have had pastoral ancestry.
Native Americans have no pastoralism ancestry therefore there’s a high degree of lactose malabsorption while
in African populations and European populations have a lower percentage of lactose malabsorption (they have
Map shows frequency differences in the gene PRLP2 between populations. Populations whose main food is
cereal grains have higher frequencies of a PRLP2 gene variant than do people who have other diets.
PRLP2 gene helps break down cereal crops (from the pancreas). There’s a higher frequency of this gene in
populations that specialize in cereals. Red depicts populations who specialize on cereal while blue depicts
populations who don’t specialize in cereal. Having a higher frequency of the gene in order to break down the
type of plant material found in cereal is an adaptation. ANTC16 Lecture 10
Thermoregulation is a force that has been thought to shape modern human variation through adaptation. There
are two rules.
Allen’s Rule: in cold climates extremities tend to be shorter than in warmer climatesBergmann’s rule: “within a
warm blooded polytypic species (species that are variable and who have multiple types) ...populations
inhabiting colder regions tend to be larger than those in warmer regions”
There is a trend (consistent with Bergmann’s
rule) but there is a lot of variation around the
line. Human body weight vs latitude is
shown on this graph. There are a lot of
populations that are low average body
weight and high average body weight.
Bergmann and allen’s rule pertain in
humans to some degree, but what really
matters is surface area to volume ratio.
In cooler climates, you want to have low
surface area compared to volume
because you want to prevent heat loss. In
hot climates, you want to have high
surface area compared to volume (want
to lose heat). In humans there are many
ways to get a low or high surface area. ANTC16 Lecture 10
Could surface area to volume explain the differences in
body shape between Lucy and Nariokotome Boy. Lucy
has a broader chest and broader pelvis than a modern
human. Lucy’s short broad chest stature can be due to
eating meat and enlarging gut (expensive tissue
hypothesis). Another alternative reason is that her short
stature has to do with thermoregulation.
The Cranial shape can also be effected by
thermoregulation. Could be do to the skull as
well. We lose a lot of heat from our head (so shape
of here really matters). One of the things that may