Lecture 45: Evolution

Introduction

• Continuation of previous Evolution topics.
• Introduction to the Hardy-Weinberg principle of equilibrium.

Hardy-Weinberg Principle

• States that allele and genotype frequencies in a population remain constant from generation to generation without evolutionary influences.
• If changes in allele frequencies are observed, evolutionary forces must be at work.

Evolutionary Influences on Populations

• Stabilizing Selection: Favors average phenotypes (e.g., human birth weight).
• Directional Selection: Favors phenotypes at one end (e.g., javelinas eating cacti with fewer spines).
• Diversifying Selection: Favors multiple distinct phenotypes (e.g., bird beak sizes for different seed types).

Microevolution vs. Macroevolution

• Microevolution: Changes in a population's genetic structure; small-scale changes.
• Macroevolution: Larger-scale changes over paleontological time.
• Both are forms of evolution differing only in the scale of changes.

Speciation and Species Definition

• Species: Group of populations capable of interbreeding and producing fertile offspring.
  • Example: Poodles and Cocker Spaniels can have fertile offspring (Cockapoo).
  • Donkeys and horses produce infertile mules.
• Speciation: Formation of new species due to evolutionary processes.

Mechanisms of Speciation

• Allopatric Speciation: Speciation via geographic separation.
  • Example: Isthmus of Panama causing porkfish speciation.
• Sympatric Speciation: Speciation in the same geographic space.
  • Driven by different selective pressures and adaptation to various niches.
  • Adaptive Radiation: A single species evolves into multiple distinct species.

Fossil Record and Evolutionary History

• Fossils provide evidence of past organisms and can be used to understand evolutionary history.
• Fossil Record: Collection of all discovered fossils.
• Fossils help piece together evolutionary history but are limited and incomplete.

Understanding Evolution Through Fossils

• Example of Whale Evolution:
  • Indo-hyas to modern toothed whales via small changes over millions of years.
  • Changes include skull and dental structure, lifestyle adaptations.
• Example of Horse Evolution:
  • Gradual limb changes from multi-fingered feet to modern hooves.

Conclusion

• Evolution involves small changes over time, leading to the diversity of life as we know it.
• Fossils, while incomplete, are essential in understanding the evolutionary pathway.
• Exam #4 will cover all topics discussed in the Evolution chapter.