AP Environmental Science

## Learning Outcomes

- Explain how **domestication** and **artificial selection** can reduce biodiversity
- Distinguish between **genetic diversity** and **species diversity** in AP Environmental Science
- Describe how **monoculture** increases vulnerability to pests, disease, and environmental change
- Use examples such as the **Irish Potato Famine** and commercial banana production to explain low genetic diversity
- Identify ways to conserve agricultural biodiversity, including seed banks, heirloom varieties, and livestock breed conservation
- Apply this topic to AP-style multiple-choice and free-response questions

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand how domestication affects biodiversity, with a focus on the following syllabus points:

- Know that biodiversity includes **genetic**, **species**, and **ecological** diversity
- Understand that domestication often reduces biodiversity by selecting a narrow set of traits or individuals
- Explain how **artificial selection** can reduce genetic variation within crops and livestock
- Identify **monoculture** as a farming practice that can further reduce biodiversity and resilience
- Understand how low genetic diversity increases susceptibility to pests, pathogens, and environmental change
- Distinguish domestication from habitat destruction: both reduce biodiversity, but by different mechanisms
- Recognise conservation strategies such as protecting **landraces**, **heirloom varieties**, **crop wild relatives**, and **seed banks**
- Connect this subtopic to wider human impacts on biodiversity in agriculture and land use

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. How does domestication reduce biodiversity within a crop or livestock species?
2. What is the difference between genetic diversity and species diversity?
3. Why does monoculture make agricultural systems less resilient?
4. How did low genetic diversity contribute to the Irish Potato Famine?
5. Name two ways humans can conserve biodiversity in domesticated species.

## Introduction

Domestication is usually taught as a success story of human agriculture. Humans selected plants and animals that were useful, easier to manage, or produced more food, and these domesticated forms became central to civilization. But for AP Environmental Science, you also need to see the ecological cost. When humans repeatedly breed organisms for a narrow set of desired traits, biodiversity often falls.

This matters because biodiversity is not only about how many species exist in a forest or coral reef. It also includes the genetic variation within a single crop or livestock species. A field of one highly uniform crop may look productive, but if nearly every plant responds the same way to drought, disease, or pests, the whole system becomes fragile.

> **Key Term: biodiversity**
> The variety of life at the genetic, species, and ecological community levels.

## Introduction

Domestication is the human-directed process of breeding and cultivating plants and animals for useful traits such as yield, size, fast growth, docility, or uniform appearance. This process has helped humans produce food more efficiently, but it often narrows the range of genes and traits found in domesticated populations.

For AP Environmental Science, the key idea is that domestication can reduce biodiversity most directly at the **genetic** level, and sometimes at the **species** level too. A food system based on a few similar crops or breeds may be productive in the short term, but it is often less stable over time.

> **Key Term: domestication**
> The human process of modifying wild plants or animals through breeding and management for desired traits.

### How domestication reduces biodiversity

Domestication reduces biodiversity because humans do not breed all individuals equally. Instead, they choose a small subset with desirable characteristics and allow those individuals to contribute more offspring to the next generation. Over time, this repeated filtering reduces variation.

This is a form of **artificial selection**. In natural selection, environmental pressures such as climate, predators, disease, and competition influence which organisms survive and reproduce. In artificial selection, humans act as the selective pressure. The result can be rapid change, but also a narrower gene pool.

> **Key Term: artificial selection**
> Human-directed breeding in which individuals with preferred traits are chosen to reproduce.

For example, if a farmer repeatedly saves seeds only from the highest-yield corn plants, genes linked to other traits may become less common. Some of those lost traits might have helped plants survive drought, poor soils, or pests. The crop may improve in one trait while losing resilience in several others.

A similar process happens in livestock. If breeders strongly select cattle for high milk yield or chickens for rapid growth, fewer genetic lines may dominate. That can reduce breed diversity and make animals more similar genetically. If a disease emerges that exploits this similarity, large numbers of animals may be affected at once.

This is why AP questions often focus on the phrase "reduced genetic diversity." Domestication does not usually eliminate a species. Instead, it often makes members of that species more alike genetically.

> **Key Term: genetic diversity**
> The variety of genes and inherited traits within a species or population.

A useful way to think about this is as a funnel. Wild populations often contain many different traits. Domestication passes only some of those traits through to future generations. The more intense the selection, the narrower the funnel.

One example from crop history is maize. Modern corn came from wild teosinte through a long domestication process. Evidence from crop research shows a strong domestication bottleneck, meaning that only a small fraction of the original genetic variation made it into later domesticated populations.

> **Key Term: genetic bottleneck**
> A sharp reduction in the number of individuals or traits contributing to future generations, causing lower genetic variation.
>
> **Test Tip:** If an AP question asks how domestication reduces biodiversity, the safest answer is usually: "It reduces genetic diversity by selecting a narrow set of traits."

### Genetic diversity versus species diversity

Students often lose marks by using "biodiversity" too vaguely. On AP Environmental Science, biodiversity has levels. For this topic, you need to separate **genetic diversity** from **species diversity**.

Genetic diversity means variation within one species. A traditional farming region with many local rice varieties has higher genetic diversity than a region that grows one uniform commercial rice strain. Even though both areas may grow "rice," one contains many more different gene combinations.

Species diversity means the number of different species in an area. A farming farm field with corn, beans, squash, fruit trees, native grasses, and pollinator plants has greater species diversity than a field planted entirely with one crop.

Domestication can reduce both, but the mechanism is different in each case.

- It reduces **genetic diversity** by repeatedly selecting a limited set of individuals or traits
- It reduces **species diversity** when agriculture becomes dominated by only a few domesticated species

For example, a region that once supported many wild plants may be converted into a large agricultural area dominated by corn, soy, or wheat. That reduces species diversity in the region. Then, within the corn crop itself, breeding for uniformity reduces genetic diversity. So one human activity can lower biodiversity at two levels at once.

This is why monoculture is so significant.

> **Key Term: monoculture**
> The cultivation of a single crop species, often a genetically uniform variety, over a large area.

Monoculture is not identical to domestication, but it often intensifies domestication's effects. Domestication is the breeding process. Monoculture is the land-use pattern that often follows.

Imagine a single disease reaches a genetically diverse group of crops. Some plants may be vulnerable, but others may have resistance. Now imagine the same disease reaches a huge field of nearly identical plants. The same weakness is shared across the field, so the disease can spread rapidly. That is why low diversity means low resilience.

> **Key Term: resilience**
> The ability of a population or ecological community to resist and recover from disturbance.

### Why low-diversity agricultural systems are vulnerable

Biodiversity matters because it acts like biological insurance. In a diverse population, not every individual responds the same way to environmental stress. Some may tolerate drought better, some may resist fungi, and some may survive sudden temperature changes. This allows at least part of the population to persist.

When domestication and monoculture reduce that variation, agricultural systems become more vulnerable to the same stressors. This can lead to crop failure, livestock disease outbreaks, and greater dependence on pesticides, fungicides, or other human inputs.

A classic case is the **Irish Potato Famine** of the 1840s. Ireland depended heavily on a limited range of potato genetic stock. When potato blight struck, much of the crop was susceptible, so failure was widespread. The important AP idea is not just that disease caused famine. It is that low genetic diversity made the food supply less able to withstand that disease.

Another useful example is the **Cavendish banana**. Commercial bananas are genetically very similar and are often propagated clonally. That makes production uniform, which is useful for transport and sale, but it also means that a pathogen can threaten huge areas of production at once. If nearly all plants are genetically alike, nearly all may share the same weakness.

Livestock can face similar problems. If breeding strongly favors rapid growth or high production, local breeds with traits such as heat tolerance, disease resistance, or ability to survive on poorer forage may decline. This matters because future environmental conditions may demand exactly those lost traits.

> **Key Term: genetic erosion**
> The loss of genetic diversity within a species, especially when traditional varieties or breeds are replaced by a few uniform ones.

Genetic erosion is especially important in agriculture. When farmers replace many local seed varieties with one commercial strain, they may gain short-term yield but lose a store of genetic options that could be vital later.

FAO work on biodiversity for food and agriculture stresses that **livestock breed diversity** is part of biodiversity. This point is easy to miss because students often focus only on wild species. But AP Environmental Science expects you to connect biodiversity to food systems too.

> **Test Tip:** If a question asks for one environmental consequence of reduced genetic diversity, strong answers include "greater susceptibility to disease," "greater pest vulnerability," or "lower resilience to climate stress."

### Conserving biodiversity in domesticated species

Because domestication narrows biodiversity, conservation efforts have to protect the diversity that remains. These efforts can happen both **ex situ** and **on farm**.

Ex situ conservation means protecting genetic material outside its original growing area. Seed banks and genebanks store seeds or other reproductive material for future use. If a variety disappears from farms, its genes may still be preserved for breeding or restoration.

On-farm conservation means continuing to grow or raise diverse traditional forms in real agricultural systems. This matters because living populations continue to adapt to local conditions.

Several terms are especially useful here:

> **Key Term: landrace**
> A locally adapted, genetically diverse crop population developed over time by farmers.
>
> **Key Term: heirloom variety**
> An older cultivated variety maintained over generations, often with more genetic variation than uniform commercial strains.
>
> **Key Term: crop wild relatives**
> Wild species related to crops that may contain useful genes for disease resistance, drought tolerance, or other adaptive traits.

Landraces and heirloom varieties are valuable because they preserve traits that may have been lost from industrial crop lines. Crop wild relatives are also critical because they can provide genes needed for future breeding, especially under climate change.

For example, if a commercial crop lacks drought tolerance, breeders may search landraces or wild relatives for useful traits. Without conserving these genetic resources, future adaptation becomes harder.

Conservation also applies to livestock breeds. A rare local breed may seem less profitable under industrial farming conditions, but it may tolerate harsh climates, local diseases, or low-quality forage better than a specialized commercial breed. Losing that breed means losing those genes.

A broader term for this whole idea is **agrobiodiversity**.

> **Key Term: agrobiodiversity**
> The variety of crops, livestock, and associated genetic resources used in agriculture.

Agrobiodiversity improves food security because it spreads risk. If one variety fails, others may survive. If one breed performs poorly under changing climate conditions, another may cope better.

This does not mean domestication is always bad or that all modern breeding should stop. AP Environmental Science usually rewards balanced thinking. Domestication has increased food production and helped support large human populations. The issue is that when breeding becomes too narrow, and when agriculture depends too heavily on uniform varieties, biodiversity and long-term resilience decline.

So the strongest exam judgement is this: domestication can be useful for production, but it often reduces biodiversity by narrowing gene pools, and this makes agricultural systems more vulnerable unless humans actively conserve diversity.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Biodiversity includes genetic, species, and ecological diversity
- Domestication is the human-directed breeding of plants and animals for desired traits
- Artificial selection can reduce biodiversity by favoring a narrow set of traits or individuals
- Domestication most directly reduces biodiversity at the genetic level
- Genetic diversity means variation within a species, while species diversity means the number of species in an area
- Monoculture is the large-scale cultivation of a single crop, often a uniform variety
- Low genetic diversity reduces resilience to pests, disease, and environmental change
- The Irish Potato Famine is a key example of the danger of relying on limited genetic stock
- Commercial banana production shows how genetic similarity can increase disease risk
- Genetic erosion happens when traditional varieties or breeds are replaced by a few uniform ones
- Conserving landraces, heirloom varieties, crop wild relatives, and livestock breeds helps protect agrobiodiversity
- Seed banks and on-farm conservation are both important methods for maintaining biodiversity in agriculture

## Key Terms and Concepts

- biodiversity
- domestication
- artificial selection
- genetic diversity
- genetic bottleneck
- monoculture
- resilience
- genetic erosion
- landrace
- heirloom variety
- crop wild relatives
- agrobiodiversity


Human Impacts on Biodiversity - Domestication reduces biodiversity