Exam: Evolution and the Human
Condition
(ZOOL30004_2022_SM1) - 90
mins
Question 1:
a) Refer to table 1 and the text. Describe the possible fitness consequences for a human living
in zone 1 that had a skin colour that was mismatched to their environment. [10 marks]
Zone 1 pertains to an annual average UV radiation of 313.2 and has 12 months where there is
adequate UV radiation to produce pre-vitamin D3. Skin pigmentation must operate within the
balance of protecting from harm--photolysis of folate/skin cancer--and benefit-allowing
enough UV for the synthesize of vitamin D. A highly skin pigmented person would be
adequately protected from the harmful aspects of UV radiation and have just enough UV for
vitamin D synthesis in zone 1. A light skin person with little melanin for skin pigmentation to
protect from UV would experience skin damage (potentially skin cancer), photolysis of folate
but have more than enough UV for vitamin D synthesis. The harmful effects of UV radiation
impact reproduction of an individual and therefore their fitness (referring to reproductive
success of an individual and their offspring's reproductive success). UV rays cause the
photolysis of folate. Folate is essential for reproduction for both males and females. In males
it is important for spermatogenesis, for females it is pivotally vital for gestation of a healthy
baby, as deficiencies in folate cause neural tube defects (spine disorders). Males will have
decreased likelihood of reproducing and females will have increased likelihood of gestating
babies that are unlikely to survive and reproduce. Thus their fitness is decreased. Notably,
skin cancer does not act as a selection pressure in these individuals as it only manifests
typically in the later stages of life after reproduction (which is where fitness refers to).
Therefore, this harmful effect of the sun does not impact on fitness and it is not selected for in
the population.
Q1, b) Within a population, female skin colour is on average lighter than male skin colour and
children typically have lighter coloured skin than adults. Explain why this might be the case
and what this suggests about the possible costs of melanisation. [5 marks]
The cost of melanisation is that there is less vitamin D being able to be synthesised by an
individual as less UV is being absorbed into the body. Lighter skin pertains to more vitamin D
synthesis. Children and females require more nutrients to grow and gestate (respectively),
, meaning that more vitamin D is required for their bodies. This will manifest as lighter skin in
these individuals compared to men. Men may experience more medical disorders associated
with vitamin D deficiencies due to this trend (depending on which zone) than women (who
may have increased likelihood of skin cancer)
Q1, c) Haplorrhines (the lemurs and lorises) and Strepsirrhines (all other primates) shared a
common ancestor approximately 65 million years ago which was likely light-skinned and had
non-colourful fur. Today, many species of Strepsirrhine, like the mandrill (Figure 1), have
brightly coloured patches of skin or fur. Describe in detail the possible steps leading to the
evolution of brightly coloured skin and fur in a mandrill. At each step, make sure you state
clearly the how (i.e. the traits that may have evolved to allow this) and the why (the benefits of
those traits). [10 marks]
Brighter skin, as mentioned, relates to less sun protection and a higher ability to synthesis
vitamin D. The common ancestor may have had light skin to allow more UV for vitamin D
sysnthesis but also used the protection of the fur to shield itself from the harsh effects of the
sun. A key difference between strepsirrhines and haplorrhines is that strepsirrhines are
nocturnal. This is indicated by strepsrrihnes noses which are slitted, with a nose pad and wet
as well their snouts which are larger than haplorrhines. These features indicate a better
sense of smell than haplorrhines and hence nocturnal existence. This is also backed up by
the presence of a tapetum in the eyes which reflects light and having dichomratic vision-all
useful for night exploring. At the night time, UV is considerably lower than the day, which
mean vitamin D synthesis is low. Vitamin D is essential for survival, and is hence associated
with mortality. This low UV pressure can can select for indivudals in strepsirrhines which
have brightly coloured skin or fur to abosrb more vitamin D at night. These indivudals will
therfore have higher fitness as they are better able to absorb vitamin D during the night and
hence survive and reproduce (lower mortality). The proportion of the individuals with brightly
coloured skin will increase and the proportion of the individuals with non-colourful skin/fur
will decrease. This means the evolution of bright and colourful skin/fur via natural selection.
Also, the brightly coloured skin does not provide a survival disadvantage (bright colours are
seen by predators and do not blend) because these animals go out at night where colour is
not as perceptible.
QUESTION 2 (either)
a) What question might an evolutionary biologist be attempting to address with this study,
and what features of the experimental design help address that question? [10 marks]
Condition
(ZOOL30004_2022_SM1) - 90
mins
Question 1:
a) Refer to table 1 and the text. Describe the possible fitness consequences for a human living
in zone 1 that had a skin colour that was mismatched to their environment. [10 marks]
Zone 1 pertains to an annual average UV radiation of 313.2 and has 12 months where there is
adequate UV radiation to produce pre-vitamin D3. Skin pigmentation must operate within the
balance of protecting from harm--photolysis of folate/skin cancer--and benefit-allowing
enough UV for the synthesize of vitamin D. A highly skin pigmented person would be
adequately protected from the harmful aspects of UV radiation and have just enough UV for
vitamin D synthesis in zone 1. A light skin person with little melanin for skin pigmentation to
protect from UV would experience skin damage (potentially skin cancer), photolysis of folate
but have more than enough UV for vitamin D synthesis. The harmful effects of UV radiation
impact reproduction of an individual and therefore their fitness (referring to reproductive
success of an individual and their offspring's reproductive success). UV rays cause the
photolysis of folate. Folate is essential for reproduction for both males and females. In males
it is important for spermatogenesis, for females it is pivotally vital for gestation of a healthy
baby, as deficiencies in folate cause neural tube defects (spine disorders). Males will have
decreased likelihood of reproducing and females will have increased likelihood of gestating
babies that are unlikely to survive and reproduce. Thus their fitness is decreased. Notably,
skin cancer does not act as a selection pressure in these individuals as it only manifests
typically in the later stages of life after reproduction (which is where fitness refers to).
Therefore, this harmful effect of the sun does not impact on fitness and it is not selected for in
the population.
Q1, b) Within a population, female skin colour is on average lighter than male skin colour and
children typically have lighter coloured skin than adults. Explain why this might be the case
and what this suggests about the possible costs of melanisation. [5 marks]
The cost of melanisation is that there is less vitamin D being able to be synthesised by an
individual as less UV is being absorbed into the body. Lighter skin pertains to more vitamin D
synthesis. Children and females require more nutrients to grow and gestate (respectively),
, meaning that more vitamin D is required for their bodies. This will manifest as lighter skin in
these individuals compared to men. Men may experience more medical disorders associated
with vitamin D deficiencies due to this trend (depending on which zone) than women (who
may have increased likelihood of skin cancer)
Q1, c) Haplorrhines (the lemurs and lorises) and Strepsirrhines (all other primates) shared a
common ancestor approximately 65 million years ago which was likely light-skinned and had
non-colourful fur. Today, many species of Strepsirrhine, like the mandrill (Figure 1), have
brightly coloured patches of skin or fur. Describe in detail the possible steps leading to the
evolution of brightly coloured skin and fur in a mandrill. At each step, make sure you state
clearly the how (i.e. the traits that may have evolved to allow this) and the why (the benefits of
those traits). [10 marks]
Brighter skin, as mentioned, relates to less sun protection and a higher ability to synthesis
vitamin D. The common ancestor may have had light skin to allow more UV for vitamin D
sysnthesis but also used the protection of the fur to shield itself from the harsh effects of the
sun. A key difference between strepsirrhines and haplorrhines is that strepsirrhines are
nocturnal. This is indicated by strepsrrihnes noses which are slitted, with a nose pad and wet
as well their snouts which are larger than haplorrhines. These features indicate a better
sense of smell than haplorrhines and hence nocturnal existence. This is also backed up by
the presence of a tapetum in the eyes which reflects light and having dichomratic vision-all
useful for night exploring. At the night time, UV is considerably lower than the day, which
mean vitamin D synthesis is low. Vitamin D is essential for survival, and is hence associated
with mortality. This low UV pressure can can select for indivudals in strepsirrhines which
have brightly coloured skin or fur to abosrb more vitamin D at night. These indivudals will
therfore have higher fitness as they are better able to absorb vitamin D during the night and
hence survive and reproduce (lower mortality). The proportion of the individuals with brightly
coloured skin will increase and the proportion of the individuals with non-colourful skin/fur
will decrease. This means the evolution of bright and colourful skin/fur via natural selection.
Also, the brightly coloured skin does not provide a survival disadvantage (bright colours are
seen by predators and do not blend) because these animals go out at night where colour is
not as perceptible.
QUESTION 2 (either)
a) What question might an evolutionary biologist be attempting to address with this study,
and what features of the experimental design help address that question? [10 marks]
