Evolutionary History of Organisms

Introduction to Evolution

Evolution refers to the cumulative changes in organisms or groups of organisms over time.
Charles Darwin proposed the Theory of Natural Selection; the idea that species evolve and adapt to their environment for survival and reproductive advantages.
Natural selection leads to speciation, producing the diversity of life known today.

Fossil Record and Dating

Fossils provide crucial evidence of organism’s evolutionary history. Fossils can be remains of an organism, traces of living organisms, or impressions.
Relative dating determines the relative age of fossils in relation to each other, but not their absolute age.
Radiometric dating determines the actual age of a fossil using the rate of decay of radioactive isotopes.

Genetic Evidence

DNA and protein similarities among species are strong evidence for common ancestry. Closer related species show higher DNA sequence homology.
Molecular clocks, using mutation rates in DNA sequences to estimate the time that two species have been evolving separately.

Analyzing Evolutionary Relationships

Taxonomy is the science of classifying organisms based on shared characteristics.
Species are arranged into a hierarchical system: domain, kingdom, phylum, class, order, family, genus, species (Do Keep Ponds Clean Or Frogs Get Sick).
Phylogenetic trees (or cladograms) are diagrams showing evolutionary relationships amongst species.

Adaptations & Natural Selection

Adaptations are characteristics that increase the fitness or reproductive success of an organism. They can be structural, behavioural or physiological.
Adaptations can lead to divergent evolution, where species with a common ancestor develop in different directions.
Convergent evolution is the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Examples of Evolution

The Peppered Moth is classic example of natural selection in response to industrial pollution.
Antibiotic resistance in bacteria is a modern example of evolution in action.

Revision summary: Understanding the evolutionary history of organisms is fundamental to the study of biology. It encompasses a wide range of topics from fossils and DNA sequencing to species classification and the role of natural selection in shaping adaptations and species diversity. Keep these key concepts in mind as you further your understanding of this complex and fascinating topic.