Humanity has grown in number tremendously. 10,000 years ago, at the end of the last ice age, we were an estimated one million. At the time of the Roman Empire we had grown to some two hundred million. At this size, we were already able to change Earth's surface significantly and, for example, deforest a large part of the Mediterranean coast hills and adjacent land areas. Today, with more 6 billion, we are more than thirty times as powerful, able to alter a large fraction of Earth's surface substantially.

And we still continue to grow. Although in some continents population growth is zero or even slightly negative, in other continents population is growing at a high rate.