Phylogenic trees

Adaptive radiation occurs when a single lineage rapidly diversifies into multiple species, typically in response to ecological opportunities or key innovations. Conditions include:

• Availability of unoccupied ecological niches

• Evolution of key adaptations (e.g., flight in birds)

• Reduction of competition (e.g., after mass extinctions)

• Geographic isolation (e.g., Darwin’s finches in the Galápagos)

Comparison of Wings in Pterosaurs, Birds, and Bats

• Pterosaurs: Wing membrane stretched along an elongated fourth finger.

• Birds: Wings are modified forelimbs with feathers supported by a lightweight skeletal structure.

• Bats: Wing membrane stretched across elongated fingers (digits 2-5).
  Despite differences, all wings are based on the tetrapod forelimb structure, showing homologous evolution.

Four Stages in the Origin of the First Cells

• Abiotic synthesis of organic molecules (e.g., amino acids, nucleotides).

• Polymerization of these molecules into macromolecules like proteins and RNA.

• Formation of protocells (membrane-bound structures capable of maintaining an internal environment).

• Development of self-replicating molecules (RNA likely played a role in genetic information storage and enzymatic functions).

Theories on the Origin of Life

• Primordial Soup Hypothesis (Miller-Urey experiment).

• Hydrothermal Vent Hypothesis (life originated in deep-sea vents).

• Panspermia (organic molecules or life arrived via meteorites).

• RNA World Hypothesis (RNA was the first self-replicating molecule).

Formation of Earth to the First Cell

• Earth formed ~4.6 billion years ago.

• Cooling led to water formation, creating conditions for organic molecules.

• Chemical evolution led to protocells.

• First true cells (prokaryotes) emerged ~3.5 billion years ago.

Significance of Water to Land Plants and Tetrapods

• Land plants need water for reproduction (early plants relied on water for sperm mobility).

• Tetrapods evolved from lobe-finned fish; adaptations like amniotic eggs and waterproof skin reduced dependence on water.

Stanley Miller’s Experiment

• Simulated early Earth conditions using a mixture of gases, water, and electrical sparks.

• Produced organic molecules like amino acids, supporting the idea that life’s building blocks could form naturally.

Protobionts and Ribozymes

• Protobionts: Membrane-bound structures with basic metabolic activity, precursors to cells.

• Ribozymes: RNA molecules with catalytic properties, supporting the RNA world hypothesis.

Mass Extinctions and Adaptive Radiations

• Mass extinctions (e.g., Permian, Cretaceous) eliminate many species.

• Adaptive radiation follows, as surviving species exploit available niches.

Genes and Development in Evolution

Exaptation Example

Goals of Phylogenetic Systematics and Key Terms

Molecular Comparisons in Systematics