Susan makes a claim that humans do not evolve because we adapt to situations by changing our technology, not ourselves. Which piece of evidence contradicts this idea? Humans have been using tools for a long time. Other primates also use tools. The size of our brains has increased since humans started using tools. Our technology is always increasing.

The cell membrane is selectively permeable, meaning it only lets certain things in and out of the cell. If you think about our building analogy, this can be a very important thing. You wouldn't want just anyone running in and out of the White House, for example. It's important to have guards who determine who's allowed in and who's not. A cell is a living thing and needs just the right balance of nutrients and water, called homeostasis. The selective permeability of the membrane allows the cell to stay in homeosis.