First paragraph (this article has no abstract)

Looked at in the large, the history of life on Earth is one of continuous change, driven by the interplay between evolutionary processes and the altered environments that can result. Some of these environmental events have had external causes (for example, the asteroidal impact that caused the most recent of the so-called Big Five mass extinctions, which eliminated the dinosaurs), while others have arisen from changing interactions among species (for example, the early appearance of oxygen in the atmosphere, resulting essentially from biogeochemical processes in primitive ecosystems). Are the recent past and impending future extinctions, unambiguously caused by humans, different? Yes and no. No, in the sense that the explosive growth of the animal species Homo sapiens can be seen as just another evolutionary process with increasingly serious ecological consequences for other species. Yes, in the sense that - unlike earlier extinctions - the causative agent (that's us) is aware of what is happening and could act to reverse current trends. Unfortunately, we show few signs of doing so.