Overtime organisms change. sometimes they change so much that descendants maybe completely different from their ancestors. what must happen for this process to occur?

The part of the eye that closes and opens to let light in is .

What is the chemical formula for dihydrogen monoxide?

After dinner with his brother, charles darwin looked through a book by thomas robert malthus, who believed that humanity, if unchecked, could double its population size in 25 years . why then , wasn't the earth overrun with humans at this point ? how does this relate to the stoning of the darwin's carriage?