Big picture: The Anthropocene is a proposed geological epoch recognising that human activities have become the dominant force shaping Earth's geology, ecosystems, and climate systems.
- Anthropocene
- A proposed geological epoch in which human activities have a significant and measurable impact on Earth's geology, ecosystems, and climate.
- Great Acceleration
- The dramatic increase in human activity and its environmental impacts since the mid-20th century, including population growth, resource consumption, and pollution.
Evidence for the Anthropocene in geological records
- Increased greenhouse gas concentrations (CO2 from ~280 to 420+ ppm)
- Widespread plastic pollution in sediments globally
- Radioactive isotopes from nuclear weapons testing (1945 onwards)
- Changes in fossil record — mass extinction of species
- Altered sediment patterns from agriculture and urbanisation
- Novel materials (concrete, aluminium alloys) in geological deposits
Proposed start dates for the Anthropocene
- The Agricultural Revolution (~10,000 years ago)
- The Industrial Revolution (~1750 CE)
- The mid-20th century Great Acceleration (most widely supported — 1950s)
Key concept: Human activities are now a major selective force, driving evolutionary changes in species at unprecedented rates.
Examples of human-driven evolution
- Peppered moth (Biston betularia) — industrial melanism during Industrial Revolution; dark moths had survival advantage on soot-covered trees
- Antibiotic resistance — overuse of antibiotics selects for resistant bacteria
- Pesticide resistance — insects evolve resistance to chemical pesticides within generations
- Pollution-tolerant fish — killifish in polluted US rivers evolved tolerance to PCBs
- Trophy hunting — elephants evolving smaller tusks or tusklessness due to poaching pressure
- Urban evolution — city birds developing different songs, rats becoming poison-resistant
IB exam tip: Use specific named examples when discussing human-driven evolution. The peppered moth and antibiotic resistance are classic IB examples.
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- Artificial selection
- The deliberate breeding of organisms by humans to select for desirable traits, resulting in domesticated plants and animals with reduced genetic diversity.
- Genetic diversity
- The total number of genetic characteristics in the genetic makeup of a species. Higher genetic diversity increases resilience to environmental change.
- Genetic bottleneck
- A sharp reduction in the size of a population, reducing genetic diversity and making the population more vulnerable to disease and environmental change.
Consequences of artificial selection for biodiversity
- Reduced genetic diversity in crop species — modern wheat has far less diversity than wild ancestors
- Monoculture vulnerability — Irish Potato Famine (1845) caused by genetic uniformity
- Livestock breeds losing genetic diversity — a few breeds dominate global production
- Loss of wild relatives as habitats are converted to agriculture
- Dependence on seed banks to preserve genetic diversity
Why genetic diversity matters
- Enables adaptation to changing conditions
- Resistance to diseases and pests
- Resilience to climate change
- Supports ecosystem stability
- Foundation for future crop improvement
IB-style question — HL — Combined human pressures + evolutionary response
Explain how multiple simultaneous human pressures on a large mammal population can amplify biodiversity loss beyond what each pressure would cause alone. Use the example of tuskless African elephants to illustrate how human activity can drive rapid evolutionary change. [4]
How to answer it, step by step
- Step 1 — Combined / synergistic impacts
• Habitat loss (deforestation for agriculture) reduces population size and fragments gene flow between elephant groups.
• Poaching for ivory simultaneously removes individuals — in particular those with the largest tusks.
• Combined, these pressures act faster than either alone: small, isolated populations have less genetic diversity AND face intense directional selection — reducing resilience to disease and environmental change. - Step 2 — Evolutionary change under human pressure
• In populations subject to heavy ivory poaching, tusked elephants are selectively killed before reproducing.
• Tuskless individuals (carrying a naturally rare allele) survive and reproduce at higher rates — natural selection is driven by human hunting, not by ecological advantage.
• Within 2–3 generations the frequency of the tuskless allele increases significantly — a measurable, human-driven evolutionary shift. - Step 3 — Consequence for biodiversity
• Tuskless elephants cannot dig for water or debark trees as efficiently → altered ecosystem engineering → changes in vegetation structure and water availability for other species.
• Loss of genetic variation for tusk size reduces the population's future adaptive potential — a form of genetic biodiversity loss.
Final answer
This is an HL question type. Award marks for: (i) naming at least two concurrent pressures and explaining why they amplify each other; (ii) a clear mechanism for the evolutionary shift (selection kills tusked individuals → tuskless allele frequency increases); (iii) a consequence — ecological or genetic — beyond simple population decline. Describing only one pressure, or only stating 'elephants evolved' without a selection mechanism, earns partial credit.
HL. HL.a — Discuss CITES Appendix I listing (international trade ban) and why it reduced but did not eliminate poaching pressure, and how domestic ivory markets can undermine international legislation. HL.b — Economics: ivory worth ~$1 000/kg on black market creates a profit incentive that conservation funding rarely matches at local enforcement level.