I think the point is that we rely on bacteria, like those found in our gut, to digest food. We are also made of millions of cells which can be thought of as "thousands of forms of life all mashed up together." I think it is interesting that everyday we have thousands of cells die and new ones produced. Think of all of the dust that is created by shedding dead skin cells. Indeed, we are individuals, but we are made of living cells. Because of the mutations of viruses and our immune systems, we could possibly (unintentionally) kill off people from the past if we were carrying some bug with us. Assuming there is some new mutation or disease in the future, our immune system would likely be overwhelmed, but people in the future may have had generations of evolution to guard them against that disease.