Lecture 10: Thermoregulation Flashcards
What type of gland is a mammary gland?
Apocrine gland
Which type of sweat gland so humans have a high density of but other mammals do not?
Eccrine gland
Where on the body do humans have the highest density of eccrine glands?
Palms of hands and soles of feet
Eccrine glands typically function in response to which type of stress?
Thermal stress
Where do other mammals have eccrine glands?
In non-hairy/furred regions (like nose and paws)
Old world primates are similar to humans in eccrine gland number and distribution with a few key differences. What are these differences?
Eccrine glands are found in hairy skin
May not be heat sensitive
What is the relationship between having a lot of body hair/fur and sweating?
mammals with hairy/furry coats would not benefit from sweating all over their bodies since their coat prevents air circulation close to skin. Sweat can only cool via evaporation and that requires air flow. A mammal that relies on evaporative cooling must have a reduced amount of body hair/fur which provides an explanation for the relatively hairless/furless body of humans.
What are some behaviors used for cooling by mammals that cannot sweat?
Panting
Covering in mud
Avoid activity during hot periods of day
Some avoid long bouts of behaviors that could overheat their bodies
How is thermoregulation related to the human ability to maintain long periods of metabolically expensive activities?
Humans ability to efficiently cool the body through evaporative cooling by sweating over large areas of the body
What is the trade off for humans being able to sweat a lot all over the body?
Fluid loss must be replenished so humans need to drink a lot of water compared to other species and humans need to consume more energy and maintain a thinker layer of fat to make up for a lack of insulation through thick hair or fur
Humans naturally have nearly ____ times the amount of body fat that would be predicted by our species average body size, but human fat cells are relatively ________ compared to other mammals/.
10 times
Small
Where are fat cells numerous in the body and why are they located here for thermoregulation?
Hypodermis because this is where heat-carrying blood vessels tend to run
How are the levels of body fat related to reproductive success?
Sexual dimorphism in fat stores is related to reproduction and higher levels of body fat increase reproductive success
Why would relatively higher amounts of fat in humans evolved with respect to offspring?
It probably evolved to support infant development and large brain growth
What is piloerection?
Erection or raising of hairs via function of the arrector pili muscles
What is thought about the location of arrector pili muscles on the bodies of early primates? Do any current species retain this?
Thought that they lacked them over their bodies and only had them in the tail. Lemurs and lorises retain this.
A weak or vestigial MAP on the body and on tail is what type of condition for primates?
Ancestral
How did lemurs and lorises evolve regarding MAP?
Prominent tail MAP but none of their bodies
What is the relationship between how tarsiers and lorises lost all MAP?
Independently
Derived state
Describe MAP on anthropoids (monkeys and apes)
Widespread over the body and tail
In many larger bodied primates what does MAP allow for?
Very strong piloerection especially on the back
In smaller primates describe MAP
Less developed on the back but very developed on the head and face
What areas are modern primates largely restricted to?
Tropical zones
What areas were early primates widely distributed and occupied?
What time period did this occur?
What did it lead to a selection for?
Northern Europe and China
Paleocene-Eocene thermal maximum (PETM)
Led to a selection for a loss or lessening of MAP density of body and tail
When was PETM and what were the temperatures like?
56mya
Global temperatures were 9 degrees warmer
What type of selection would a possible coat thickness reduction be considered when reducing body heat as found in early primates?
Positive selection
A retention of MAP in the tail for ancestral lemur maight have been related to what?
Tail use in locomotion for leaping
What were some ways that smaller primates adapted to conserve their body heat post PETM?
High energy diets Being active during cooler parts of the day Sunning Huddling Hibernation during cold/dry seasons
During the middle Eocene what would the ancestral anthropoid require regarding MAP?
All over their body and tail
What happened to those during Late Eocene, post PETM ?
If they could not adapt they died out at higher latitudes
What contributes to the human skin color?
Hemoglobin from blood
Carotene from diet
Melanin
What type of trait is skin color?
Polygenic
What is the form of melanin called in darker skin?
Eumalanin
What is the form of melanin called in lighter skin?
Pheomelanin
What are the functions of melanin?
Absorb sunlight
Protect dermis from solar radiation
Skin color of different populations correlates _____________ with ____________ and potential exposure to UV radiation
Inversely
Latitude
Why might hominins evolving in sub-Saharan Africa might have developed melanin?
It was probably essential as body hair was reduced to protect from intense direct sunlight year round
What is the sunlight like in higher latitudes like Europe and Asia?
Does not strike the Earth as directly and less intense
At very high latitudes the amount of sunlight sees dramatic seasonal shifts
What is a hypothesis for vitamin D?
Humans migrating from lower latitudes to higher latitudes will have a shortage of vitamin D3 unless melanin production is reduced
Select for lighter and lighter pigmentation as you move further and further from the equator
What is some criticism for the vitamin D hypothesis?
Stems from a lack of evidence to support the idea that people with different levels of skin pigmentation and latitudes actually have a clinically significant difference in vitamin D synthesis
Modern medicine, diet and behavior only serve to further complicate this issue
What is the solar protection hypothesis?
Habitat and climate variable appear to account for 80% of observed variation in skin color
Still, the biogeography of human population skin pigmentation variation in the New World vs the Old World and Pacific Islands leaves a lot of questions
What is the camouflage hypothesis for skin pigmentation?
Darker coloration is adaptive for hungers and human prey in tropical forests
Lighter skin might be effective in arctic areas
What is the hypothesis of protection of nutrients in skin coloration?
Melanin may protect folates from breakdown
What is the hypothesis for protection against tropical disease?
Some evidence that melanin has a role in protecting the skin from microbes
What is the hypothesis for thermoregulation and skin coloration?
Darker skin may be able to conserve more energy that would be lost to thermoregulation because melanin absorbs radiation and allows solar heating of skin
Would be a disadvantage in the tropics though
What is the hypothesis of sexual selection for skin coloration?
Like tends to attract like
Would lead to a pattern of positive assortative mating that would exaggerate differences among populations
Would see an increase in diversity of traits that had little adaptive value
