About 65 million years ago, life on Earth was stressed by global climate change and rising sea levels. At this time, two large asteroids struck the planet simultaneously in North and South America. The impacts threw a huge dust cloud into the atmosphere and blocked the sun for at least several months. They also coincided with the extinction of the large dinosaurs and profound changes in other life.

Biologist Peter Ward has called attention to similarities between that time and our own. Climate change and rising sea levels are stressing the world's biota again and, to use Ward's analogy, another ‘asteroid’ struck in Africa about 100000 years ago – the evolution of the human species. Ward argues that the rise of humans has meant the diminishment of the great diversity of life on Earth, in just the same way as the impacts of the earlier asteroids altered the direction of evolution.

In this first theme of Environmental Biology we examine why an understanding of our species is essential to understanding and conserving the diversity of life.