Humans

Humans, taxonomically defined as Homo sapiens, are bipedal land mammals living on every continent and a large fraction of the islands on Earth. The human race is one of the few individual species in Earth history, and probably the only species of animal, to have achieved such massive influence over Gaia's basic systems as to trigger a mass extinction-level disruption on a planetary scale. This has occurred largely as a result of the recent Industrial Revolution and the accompanying human population explosion (from under 1 billion to over 7 billion in just the past two centuries), although humans have caused extinctions of megafauna through overhunting for many thousands of years.

Due to our exceptionally high intelligence, humans have also contributed to the establishment of many new forms of diversity, such as cultural, technological, artistic, and ideological diversity. Thus, like the cyanobacteria that destroyed countless anaerobic species by adding oxygen to the atmosphere two billion years ago, we have created a vast range of new possibilities through the same processes that have led to massive ecological damage. Unlike bacteria, humans also demonstrably have the capacity to change our behavior to reduce the harm we do to Gaia and even reverse it through ecological restoration efforts. More speculatively, humans might provide future benefits to Gaia by deflecting killer asteroids and spreading life to other worlds through ecopoeisis.