Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 53.6 The Human Population Is No Longer Growing Exponentially but Is Still Increasing Rapidly
The human population has experienced explosive growth in recent centuries but is now expanding at a slower pace. Although growth is no longer exponential, it remains rapid and uneven across regions. Understanding age structure, fertility, and ecological limits is key to forecasting population trends and global sustainability.
1. Global Growth Trends
- 1650: 500 million → Today: 7.6+ billion
- Doubling time: 200 years → 45 years
- Growth rate peaked: 2.2% (1962) → 1.1% (2018) → projected 0.5% (2050)
- Still adding 80+ million people annually
2. Age Structure
- Age structure diagrams show age distribution:
- Zambia: broad base → rapid growth
- USA: even distribution → slow growth
- Italy: narrow base → likely decline
- Structure impacts future population, economy, and services
3. Infant Mortality and Life Expectancy
- Angola: 7.1% infant mortality, 59-year life expectancy
- Japan: 0.2% infant mortality, 85-year life expectancy
- These influence reproductive decisions
4. Demographic Transition
- Shift from high to low birth and death rates due to:
- Industrialization, healthcare, education
- Sweden: slow transition over 150 years
- Mexico: transition in progress
- China: fertility dropped from 5.9 → 1.6
- Many developed countries now have sub-replacement fertility (<2.1)
5. Carrying Capacity and Resource Limits
- Carrying capacity estimates vary (e.g., 13.4 billion)
- Constraints: food, land, water, energy, waste absorption
- Depends on consumption patterns and technology
6. Ecological Footprint
- Footprint: land/water needed for resource supply and waste removal
- U.S.: 8 global hectares (gha)
- World average: 2.7 gha (above sustainable limit of 1.7 gha)
- Energy inequality: rich countries use ~30× more energy than poor ones
- Fossil fuels: ~80% of energy in developed nations
7. Sustainability Challenges
- Food distribution is a bigger issue than food supply
- Water scarcity: affects over 1 billion people
- Waste and fossil fuel use reduce long-term carrying capacity
- Growth will eventually stop—by choice or crisis (e.g., famine, war)
In a Nutshell
Though human population growth has slowed from exponential levels, it remains rapid and uneven globally. Age structure, fertility, and resource use patterns will determine our future. Sustainable living depends on balancing population size with the ecological footprint—through innovation, education, and collective choices about consumption and equity.