Table of Contents
Overview: What This Part of the Course Is About
In this block of the course, “Evolution and Biological Diversity,” you will look at how living things came to be the way they are and why there are so many different forms of life on Earth.
Earlier parts of the course deal with what life is and how it works right now (cells, metabolism, genetics, ecology). This part focuses on the historical dimension: life through time.
You will not yet go deep into the details listed in the subchapters (those will each have their own sections). Instead, this chapter orients you: what “evolution” means in biology, how it connects to biodiversity, and how the upcoming chapters fit together.
Evolution: Change of Life Through Time
In biology, evolution means:
Gradual change in inherited characteristics of populations over many generations.
Key points that are important as a foundation:
- Evolution acts on populations, not individuals. Individuals are born, live, and die; populations change in their genetic composition over time.
- These changes are heritable (passed through DNA from parents to offspring).
- Evolution explains both:
- Adaptation: how organisms come to fit their environments.
- Diversity: why there are so many different species and forms.
You will later learn about specific evolutionary factors like mutation, selection, and genetic drift. For now, remember that evolution is not simply “individuals getting better during their lifetime,” but rather shifts in which genes are common in a population over long periods.
Biological Diversity: Variety of Life on Earth
Biological diversity (biodiversity) describes the variety of life at several levels:
- Genetic diversity – differences in DNA within a species (e.g., different human eye colors, dog breeds, crop varieties).
- Species diversity – the number and variety of different species (e.g., birds vs. insects vs. fungi in a forest).
- Ecosystem diversity – different habitats and communities (e.g., coral reefs, rainforests, deserts, tundra).
In this part of the course, the focus is mainly on how evolution produces and shapes this diversity, not on conservation issues (those appear later in Ecology and Nature Protection).
How Evolution and Diversity Are Connected
Evolution and biological diversity are inseparable:
- As populations evolve and split into new lineages, new species arise.
- Over hundreds of millions of years, this repeated branching produces the tree of life: a vast pattern of relationships among all organisms.
- Extinction removes branches from this tree; speciation creates new ones.
- The result is the current biodiversity we see today, as well as the huge diversity we know only from fossils.
Three important connections:
- Common ancestry
All living organisms share more or less distant common ancestors. This means: - Similarities between species often reflect shared evolutionary history.
- Differences reflect divergence over time in different environments.
- Adaptation and radiation
When a lineage encounters new conditions (new habitats, food sources, or after mass extinctions), it can undergo adaptive radiation: - Many new species evolve from one ancestor.
- Each occupies a different ecological niche.
This process is a major generator of biodiversity. - Historical contingency
Evolution does not follow a plan. Chance events (mutations, environmental changes, asteroid impacts) influence which lineages survive and diversify. Current biodiversity is the outcome of both: - Predictable processes (like natural selection),
- And unique historical events.
The Structure of This Part of the Course
Each subchapter under “Evolution and Biological Diversity” will explore a different angle on how we know evolution happens, how it works, and what patterns it produces.
1. History of Evolutionary Thought
This section is about ideas, not the biological mechanisms themselves. It traces how humans have tried to explain the origin and diversity of life:
- Creation myths and early philosophical ideas.
- First attempts at scientific explanations of descent.
- The shift from vitalism (special “life force”) to mechanistic explanations.
- Development of modern evolutionary theory, especially Darwin’s proposal of natural selection and comparisons with Lamarck’s idea of inheritance of acquired characteristics.
- Hypotheses about the origin of life itself (e.g., RNA world).
This gives you historical context for why evolution is such a central unifying concept in biology.
2. Evidence for the Evolution of Organisms
Here you will see how we know evolution is real, using different kinds of observations:
- Fossils and transitional forms show changes over geological time.
- Development (ontogeny) can reveal traces of evolutionary history in embryos.
- Homologous structures (same origin, different function) vs. analogous structures (different origin, similar function).
- Rudimentary organs and atavisms (leftover or reappearing ancestral features).
The focus is on recognizing patterns that make sense only if life has a common history.
3. Evolutionary Factors and Their Effects
This is where you will study the mechanisms that actually drive evolution in modern terms, often called the Synthetic Theory of Evolution:
- Mutation and recombination create genetic variation.
- Natural selection filters that variation based on its effect on survival and reproduction.
- Genetic drift introduces chance changes in small populations.
- Isolation and speciation explain how new species can form.
You will also see extensions and alternative ideas that refine, not replace, the basic framework.
4. Symbiogenesis
This part emphasizes that evolution is not only about competition, but also about cooperation and living together:
- Different types of relationships: competition, symbiosis, commensalism, antibiosis.
- The endosymbiotic theory: how early symbioses between prokaryotes gave rise to eukaryotic cells (cells with nuclei and organelles like mitochondria and chloroplasts).
This shows that some of the most important evolutionary innovations may come from fusion and cooperation between lineages.
5. Phylogeny and the Diversity of Life
Here the focus shifts to reconstructing the evolutionary tree:
- Patterns of evolution (branching, convergent evolution, adaptive radiations).
- Methods of phylogenetic research: how scientists infer evolutionary relationships from morphology, molecules, and other data.
This provides the conceptual link between evolutionary processes and the classification of organisms you will meet later.
6. Human Evolution
This section applies evolutionary thinking to our own species:
- Where humans fit within the primates.
- The human fossil record and how it documents major changes (bipedalism, brain size, tool use).
- Discussion of “human races” in a biological and historical perspective.
- The origin of modern humans and the roles of migration and interbreeding.
- Cognitive and cultural evolution, which interact with biological evolution.
This shows that humans are part of the same evolutionary story as all other life, while also having unique cultural dimensions.
7. Classification of Diversity (Systematics)
Finally, you will learn how biologists organize and name the diversity of life in a way that reflects evolutionary relationships:
- Basic terms and definitions in systematics (like species, genus, family, domain).
- The three major domains: Archaea, Bacteria, and Eukarya.
- Within Eukarya, the main kingdoms: Protista, Plantae, Fungi, Animalia.
This chapter connects evolutionary relationships with the practical system used to classify organisms.
How This Part Links to Other Topics
While you go through “Evolution and Biological Diversity,” keep in mind connections to other parts of the course:
- Genetics explains how heredity works at the molecular level; here you see how genetic changes accumulate over time in populations.
- Ecology describes how organisms interact with their environments and each other; evolution explains how those interactions shape and are shaped by adaptation.
- Disease and Health often involves evolving pathogens (like viruses and bacteria); understanding evolution helps explain antibiotic resistance and emerging diseases.
- Behavioral biology looks at behavior; in this block you see how behavior can itself evolve and influence evolutionary success.
Together, these parts show biology as a coherent whole: life’s structure and function today make sense only in light of its evolutionary history and the diversity that history has produced.