1. Low human population densities on Polynesian islands were caused by a lack of resources for farming. 2. The main resource was water, but soil quality was also important. 3. Some islands could not grow tropical plants, while others did not have enough rain or poor soil.

Jared Diamond argues that Europeans conquered the Americas due to their technological superiority, symbolized by "guns, germs, and steel." Europeans had advanced military technology and brought diseases that devastated native populations, making conquest easier. These advantages stemmed from their long history of farming, which was possible due to geographic luck. This early agricultural development led to more complex societies capable of producing advanced technologies and organized political structures.

Diamond attributes the late domestication of American apples to several factors: the nomadic lifestyle of Native Americans, which did not encourage the development of sedentary agriculture, and the technological challenge of grafting required for apple cultivation. He suggests that while indigenous peoples had sufficient wild resources, they did not prioritize apple domestication due to the lack of other domesticable plants and animals to support a settled lifestyle, compounded by the arrival of Europeans.

Diamond views the Polynesian Islands as a "natural experiment" of history, illustrating how environment influences cultural evolution. The Polynesians colonized various Pacific islands, starting from a common origin, but each island's unique environment led to different societal developments. For example, New Zealand's climate supported complex societal evolution, while the Chatham Islands favored hunter-gatherer lifestyles. This divergence demonstrates that environmental factors, rather than race or culture, play a crucial role in societal development.

Diamond likely would not accept continent-wide differences in innovation receptivity unless only a few distinct societies exist on that continent. He argues that societies are too varied to generalize across continents. Cultural differences are acknowledged, but Diamond contends they are random and not continent-specific. His theories would face challenges if significant and consistent cultural differences were found between continents, such as between African and European societies.

The development of irrigation in "Guns, Germs, and Steel" is discussed as a theory, not proposed by Diamond, suggesting that irrigation required centralized bureaucracies, thus enabling civilization. However, Diamond rejects this theory, arguing that large-scale irrigation systems did not directly lead to the mental or political development of river civilizations. Instead, he notes that such systems emerged after states were formed, and irrigation was a secondary factor, not the primary cause of development.

The collision between the Maori and Moriori tribes is considered a "small-scale natural experiment" because it illustrates how two groups with the same cultural origins reacted differently due to their distinct environments. The Maori settled in agriculturally favorable New Zealand, while the Moriori inhabited the less hospitable Chatham Islands. This situation allowed Jared Diamond to assess whether environment or culture had a greater impact on societal power, demonstrating that environmental factors were more influential in this case.

In Guns, Germs, and Steel, Jared Diamond explains that human migration from Africa to Australia and the Americas occurred due to the adaptability and exploration instincts of early humans. These migrations were facilitated by changing climates, land bridges, and technological advancements that allowed humans to survive and thrive in diverse environments, ultimately leading to the widespread distribution of human populations.

In Guns, Germs, and Steel, Jared Diamond describes Africa's human diversity as a result of its vast geographical and environmental variety. This diversity is reflected in the continent's numerous languages, cultures, and ethnic groups, which have evolved over millennia due to differing climates, landscapes, and historical migrations.