Modern Human Variation

Question 1

what four factor affect human variation

Answer 1

• Neutral genetic processes and geography
• Population history and genetic adaptation
• Developmental plasticity and epigenetics
• Culture, ways of life, and self-ascribed group identity
  
  • Our cultural changes have influenced the selective pressure influencing our genetics. This leads to cultural-genetic coevolution (gene culture coevolution). A great example is Agriculture.

Question 2

what affects our environment

Answer 2

Environment: Characteristics of environmental stress:

• Climatic variation
• pollutants
• UV radiation
• disease
• Parasites
• Predaotrs
• food availability
• energy availability
• social life

Question 3

how do we use culture and technology

Answer 3

Culture and Technology: Technological mediation of environmental stress:

• Housing
• Clothing
• Climate control
• Agriculture
• Medicine

Question 4

how does our physiology and development adapt us

Answer 4

Physiology and Development: Developmental adaptation and plasticity within the lifespan:

• Growth
• Physiology
• Dietary flexibility
• Body fat

→ Epigenetic regulation

Question 5

how do our genetics adapt us

Answer 5

Genetic Adaptation: Intergenerational genetic adaptation:

• natural selection
• changes in gene frequency

Question 6

what influences selection

Answer 6

Environmental Stress influences selection

Human shift adaptations onto cultural evolution, technological solutions, and physiological and developmental plasticity

Question 7

what is plasticity

Answer 7

Plasticity: one genotype can produce different phenotypes depending on environmental conditions (Epigenetics)

Epigenetics is a significant and dynamic mechanism responsible for human phenotypic plasticity

Question 8

what is an example of a challenge for our bodies

Answer 8

Thermoregulatory challenges have provided much of the driving force for adaptation in humans

Core temperature (Organs and brain) - needs to stay between 36 and 38ºC

It is very energetically expensive to actively thermoregulate!

Question 9

how could we succeed globally

Answer 9

we reduce the cost of thermoregulation with our culture and technology

• Clothing, housing, air conditioning, central heating, insulation, evaporative cooling

But culture, technology, and plasticity cannot remove all of the stress imposed by climate, or by other environmental stressors

Adaptation happens at the extremes of tolerance.

Question 10

describe the graph of tolerance

Answer 10

Population size vs Environmental condition represents a bell curve

Highest population at ideal condition

Below lower limit of tolerance + above upper limit of tolerate = Zone of intolerance (species is absent)

Between upper/lower limit of tolerance and the upper/lower range of optimum is zone of physiological stress (low population)

Range of optimum has greatest abundance

Question 11

where does adaptation occur

Answer 11

Adaptations happens at extremes of tolerance. Here, presence or absence of a specific characteristic, or pattern of adaptability, will most influence fitness of survivorship.

Question 12

how do neutral genetic process affect craniofacial diversity

Answer 12

• Most variation globally is due to neutral genetic processes like genetic drift
  
  • Most craniofacial variation is just random
  • Within-group diversity decreases the further that population is from sub-Saharan Africa
• The mandible is doing something different
  
  • More to the story here than just neutral genetic processes

Question 13

how does developmental plasticity affect craniofacial diversity

Answer 13

You are what you eat

• loading the muscles that close your mouth can influence the dimensions of your face and jaws

Variation in features directly involved in chewing:

• Attachments for the temporalis muscle
• relative position and size of upper dental arch and muscles
• length and breadth of the mandible

Question 14

how does adaptation to extreme cold affect craniofacial diveristy

Answer 14

• Signatures of climatic adaptation only in the regions involved in thermoregulation
  
  • Face and nose shape: warming incoming air (smaller in arctic)
  • Breath of the skull: surface-area to volume

Signatures of climatic adaptation only seen in Arctic populations → Buriat and Inugskul

extreme cold can drive natural selection among certain human populations in traits associated with thermoregulatory capacity