Tennessee Biology I EOC LS4 (Evolution and Classification): a complete overview of the evidence for common ancestry, natural selection, speciation, classification, and biodiversity

What the LS4 biological-change core idea demands

Biological Change: Unity and Diversity (LS4) is the evolution core idea of the Tennessee Biology I course. This guide runs from the evidence that life shares common ancestors, through the mechanism (natural selection) and how it produces new species, to how we organize the diversity (classification) and why that diversity matters (biodiversity). The recurring crosscutting concept is patterns: the patterns in fossils, anatomy, molecules, and family trees all point to descent with modification.

This guide ties together the matching topic pages, each with its own practice questions: the evidence for common ancestry, natural selection and adaptation, speciation and population change, classification and phylogeny, and biodiversity and its importance.

The evidence for common ancestry

Several independent lines of evidence support common ancestry: the fossil record (life has changed over time; transitional forms link groups), homologous structures (same anatomy from a shared ancestor, such as vertebrate forelimbs), vestigial structures (reduced remnants of ancestral features), embryology (related species look alike as embryos), and the strongest modern line, molecular evidence (the more similar two species' DNA or proteins, the more recently they shared an ancestor). Because so many lines agree, the case is strong.

Natural selection and adaptation

Natural selection needs variation, overproduction and competition, differential survival and reproduction (fitness), and inheritance. Over generations, favorable heritable traits become more common, producing adaptation. Fitness means reproductive success, not strength. Selection acts only on existing variation (from mutation and sexual reproduction) and changes the population, not the individual. Antibiotic resistance and camouflage are classic examples.

Speciation and population change

When the environment changes, selection favors different traits and allele frequencies shift. Speciation is the formation of a new species, often beginning with reproductive isolation (commonly a geographic barrier). Separated groups accumulate different changes; if they can no longer interbreed, they are separate species. When variation cannot meet a challenge, a population may instead go extinct.

Classification and phylogeny

Organisms are classified in a nested hierarchy: domain, kingdom, phylum, class, order, family, genus, species. Three domains (Bacteria, Archaea, Eukarya) sit at the top. Each species has a two-part Latin name (binomial nomenclature). Modern classification groups organisms by evolutionary relationship, using molecular and structural evidence. A phylogenetic tree (cladogram) shows relatedness: species sharing a more recent branch point are more closely related.

Biodiversity

Biodiversity has three levels: genetic, species, and ecosystem diversity. It arises through evolution (mutation, selection, speciation). Genetic variation lets a population survive change by containing individuals that can cope. High biodiversity supports ecosystem stability and resilience through redundancy among species, and provides benefits to humans (food, medicines, materials, pollination, clean air and water).

Check your knowledge

A mix of recall and reasoning questions covering the LS4 biological-change core idea. Attempt them under timed conditions, then check against the solutions.

1. Name four lines of evidence for common ancestry. (2 marks)
2. State the difference between homologous and analogous structures. (2 marks)
3. List the four conditions for natural selection. (2 marks)
4. Explain what biologists mean by fitness. (1 mark)
5. Explain how a geographic barrier can lead to speciation. (3 marks)
6. State why a population might go extinct when its environment changes. (1 mark)
7. List the taxonomic hierarchy from broadest to most specific. (2 marks)
8. On a cladogram, what does it mean if two species share a more recent branch point? (1 mark)
9. Explain why a population with high genetic variation is more likely to survive a new disease. (2 marks)