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Notes on Human Evolution and Adaptations

Introduction to Human Evolution

  • Understanding key concepts of human evolution and related traits.

Learning Objectives

  • Describe the adaptive advantages of the amniotic egg: Protects embryo, facilitates gas exchange, and reduces water loss.

  • Explore the derived traits of mammals and primates: Identify unique traits that distinguish these groups.

  • Examine the evolution of early hominins: Understand the timeline and defining characteristics of early human ancestors.

  • Define unique traits of Homo sapiens: Focus on traits that have contributed to human success.

  • Consider why Homo sapiens have been so successful: Explore social and cultural factors influencing success.

Amphibian Characteristics

  • Salamanders: Can be aquatic, terrestrial, or a mix; some species lack lungs, cutaneous breathing through skin

  • Frogs: Exhibit different developmental stages, complete metamorphisis (aquatic larvae vs. terrestrial adults); known for vocalizations and aposematism (warning coloration, poisonous), Toads are not monophyletic

Vertebrate Phylogeny

  • Key Groups in Chordate Evolution:

  • Amniota: evolution of the amniotic egg.

  • Tetrapoda: adaptation to land.

  • Major classes include Myxini, Petromyzontida, Chondrichthyes, and others.

Amniotic Egg Structure

  • Components: Includes chorion: gas exchange, amnio: fluid filled cavity protects embryo, yolk sac: holds nutrients, allantois: metabolic waste, and provides a protective fluid-filled cavity.

  • Functionality: Allows for gas exchange and nutrient supply while protecting the developing embryo.

Derived Traits of Amniotes

  • Egg adaptations: Shells or internal gestation help reduce water loss in embryos

  • Skin: Less permeable skin reduces water loss in adults, dry scaled skin

  • Rib cage: Aids in ventilation and efficient gas exchange, thoracic breathing

Reptilian Adaptations

  • Physical Traits: Scales and feathers are keratin-based, avoiding desiccation.

  • Reproduction: ALL REPTILES Lay shelled eggs on land with internal fertilization prior to shell secretion

  • Temperature Regulation:

    • Ectothermic (e.g.,lizards, snakes, turtles) vs. endothermic (e.g., birds).

    • Ectotherms seek warmth externally to regulate body temp.

    • Endotherms have their own heat internally

  • Lizards, Snakes, and Turtles

    • Lizards:

      • Few cm to 3 meters large

      • Broad diet, can eat a lot of different foods

    • Snakes:

      • Lizards to snakes (legs lost)

      • Adapted for hunting

    • Turtles:

      • Shells fused to vertebrae and ribs

      • Can be terrestrial, freshwater, and marine

      • All lay their eggs on land

Evolution of Mammals

  • Derived Traits of Mammals:

  • Presence of mammary glands, endotherms, hair, and a fat layer under skin.

    • Endothermic with larger brains, extended parental care, and diverse tooth structures.

Types of Mammals

  • Monotremes: Eggs, mammary glands but no nipples (e.g., platypus, echidna).

  • Marsupials: Early development in simple placenta, further maturation of embryonic development outside uterus (e.g., kangaroos, kangaroos).

  • Eutherians: Complete development occurs in the uterus, further developed placenta, longer gestation(e.g., most mammals).

Derived Traits of Primates

  • Adaptations: Grasping hands and feet, flat nails, large brains relative to jaw size, telescoped eyes for better hand-eye coordination, opposable thumbs

  • Special Features: Monkeys and apes possess opposable thumbs.

Derived Traits of Hominins

  • Key Characteristics:

  • Bipedalism, larger brain capacity, complex thoughts, tool usage, reduced jaw structure.

Hominin Evolution Timeline

  • Early Hominins:

  • 6.5 MYA: Signature features include upright posture and reduced teeth sizes.

  • Notable Species: Australopithecus (various), Homo habilis, Homo erectus, and more.

Evolution of Homo

  • Homo Erectus:

  • Height approximately 5-6 ft, utilized fire, migrated out of Africa.

  • Homo Neanderthalensis:

  • Adapted to cold, stocky physique, lived alongside early Homo sapiens.

Characteristics of Homo sapiens

  • Physical Traits: Lighter skeletons with smaller teeth; advanced tool making and cultural practices.

  • Social Development: Emergence of complex societies.

Dispersal of Homo sapiens

  • Migration Timeline: Originated in Africa, spread to Middle East, Europe, Asia, Australia, and the Americas.

Interactions Between Hominins

  • Genomic Evidence: Indications of interbreeding with Neanderthals; about 1-4% of DNA in modern humans sourced from them.

Reasons for the Success of Homo sapiens

  • Coexistence: Early Homo sapiens shared environments with other species; lifestyle changes led to their dominance.

  • Adaptations: Advanced tools, social structures, and cultural developments led to advantages.

Exam Preparation Tips

  • Understand Evolution: Know how groups are positioned on phylogenetic trees.

  • Adaptation Assessments: Analyze the adaptive significance of derived traits.

  • Comparison of Groups: Identify shared and distinctive traits between taxonomic groups.

Resources for Study

  • Review assignments and resources available in your course materials, including SmartBook, practice questions, and student hours for questions and clarifications.

  • Focus on key traits and relative dates for significant evolutionary milestones.