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.