One of my favourite books - showing how the effects of geography, climate, botany etc. led to the shape of the modern world. Why did Europeans conquer other continents rather than the other way round? Why did some people remain in the stone age?
Big mammals of Africa/ Eurasia survived into modern times, coevolved with protohumans for millions of years and learnt to be scared of us. Things like dodos, moas and the megafauna of Australia and the Americas were wiped out when they encountered modern humans with weapons and hunting skills.
New Guinea and Australia had no wild animals that might have been candidates for domestication.
Of the five habitable continents, North America and South America are the ones with the shortest human prehistories.
The larger the size of the landmass and the higher the population density, the more complex and specialized were the technology and organization. No urbanisation without big enough population to support it.
Peas were domesticated by 8000 B.C., olives around 4000 B.C., strawberries not until the Middle Ages, and pecans not until 1846.
(Detailed look at plant domestication and breeding by humans.)
The wild species suitable for domestication were mostly confined to Eurasia (few exceptions - Llamas, Guinea Pigs in the Andes).
The main axis of the Americas is north-south, forcing most diffusion to go against a gradient of latitude (and climate) rather than to operate within the same latitude. For example, wheels were invented in Mesoamerica, and llamas were domesticated in the central Andes by 3000 B.C., but 5,000 years later the Americas’ sole beast of burden and sole wheels had still not encountered each other, even though the distance separating Mesoamerica’s Maya societies from the northern border of the Inca Empire (1,200 miles) was far less than the 6,000 miles separating wheel- and horse-sharing France and China.
Size of the regional population is the strongest single predictor of societal complexity.
New Guinea has by far the highest concentration of languages in the world: 1,000 out of the world’s 6,000 languages.