Unit 2_ Human Variation & Adaptation

UNIT 2: MODERN HUMAN VARIATION

• Course lead: Dr. Hilary Morland

• Contact: hmorland@msudenver.edu

Overview of Topics

• Human Variation & Adaptation (Chapter 14)

  • Types of human variation

  • Adaptations

  • Lactose intolerance

  • Skin pigmentation

• Human Osteology

  • Structure of the human skeleton

  • Adaptations for bipedalism

  • Lab 3: Osteology

• Forensic Anthropology & Bioarchaeology (Chapter 15)

  • Techniques for identifying age and sex from skeletons

  • Identifying trauma, disease, and cultural modifications

  • Lab 4: Forensic

• The Concept of Race (Chapter 13)

  • Evolutionary basis of skin color

  • Discussion on the definition of race

  • Class activity

Human Variation

• Types of Variation

  • Important variations in humans and their social perceptions.

Genetic Variation

• General Facts

  • Homo sapiens is a relatively young species with limited time to accumulate genetic variation.

  • While genetic variation exists, the human genome has approximately 3 billion base pairs.

  • Approximately 0.1% variation exists between any two individuals.

  • Each person, except identical twins, is genetically unique.

• Distribution of Genetic Variation

  • About 85% of genetic variation exists within populations, while only 15% exists between populations.

  • Humans are considered to be one continuously variable, interbreeding species.

• Genetic Variation Among Populations

  • African populations have greater genetic variation compared to European or Asian populations due to their longer existence in Africa.

  • Genetic variation in populations outside of Africa is a subset of African variation.

Types of Variation

• Discontinuous Variation

  • Present or absent; measurable and classifiable into categories.

  • Often Mendelian traits influenced by few genes (e.g., tongue rolling: dominant T vs. recessive r).

• Continuous Variation

  • Traits exist on a spectrum and are most often polygenic (controlled by multiple genes).

  • Geographical and environmental influences visible in traits like height, weight, and skin color.

  • Example: Height is influenced by approximately 80% genetics and 20% environmental factors.

• Clinal Variation

  • Gradual variation in gene frequency or phenotype across geographical ranges.

  • Example: Skin color is darker around the equator and lighter towards the poles.

• Sexual Dimorphism

  • Systematic morphological differences between male and female individuals of the same species.

  • Examples: Typically, males are larger than females, which may be linked to competition among males.

• Non-Concordance

  • Phenotypical traits that are independent of one another.

  • Example: Height does not determine hair color.

Human Variation Detailed Concepts

• Polymorphism: Variation in alleles of a single trait.

• Polygenic Traits: Traits influenced by multiple genes with non-Mendelian inheritance.

• Pleiotropy: One gene affects multiple traits (e.g., PKU affects multiple physiological traits).

• Polytypic: Differences in local populations regarding specific traits.

• Continuous vs. Discontinuous Variation: Differences in expression level of traits.

Human Adaptations

• Adaptations are population responses to local environmental conditions, which help maintain normal body functioning and enhance fitness.

• Lactose Intolerance:

  • Worldwide, about 68% of people experience lactose malabsorption in adulthood.

  • Some populations demonstrate higher rates of lactose tolerance due to cultural and dietary practices.

• Mammalian Milk and Lactose:

  • Milk is critical for infant development, containing lactose which is vital for nutrient absorption.

  • Lactase is required to digest lactose, with most adults experiencing a decrease in lactase production post-infancy, leading to intolerance.

• Lactase Persistence:

  • Relates to the ability to digest lactose in adulthood, linked to certain gene variants (LCT).

  • Evolved in populations where dairy was a significant food source, improving survival under certain conditions.

  • Geographical Patterns: High lactase persistence is noted in Northern Europe and certain populations in Africa.

Physiological Adaptations to Climate**

• Heat Stress: Adaptations such as sweating and vasodilation for temperature regulation.

• Cold Stress: Vasoconstriction preserves heat, while shivering increases metabolic rate.

• Bergmann’s Rule: Colder regions have larger body masses.

• Allen’s Rule: Extremities are shorter in colder climates to preserve heat.

• Examples in Humans: Canadian Inuit adapted to cold with stockier builds, while East African populations are more linear.

Developmental Adaptations**

• Individuals born in extreme environments can show permanent physiological changes (e.g., broad chests for better oxygen capacity in high altitudes).

Summary of Human Variation Concepts**

• Variation can be classified into categories including continuous, discrete, clinal distributions, and non-concordant traits based on environmental and cultural conditions.