What is mitosis and meiosis?

There are two types of cell division: mitosis and meiosis. Most of the time when people refer to “cell division,” they mean mitosis, the process of making new body cells. Meiosis is the type of cell division that creates egg and sperm cells. Mitosis is a fundamental process for life. Mitosis is the division of a cell into two daughter cells that are genetically identical to the parent cell. Meiosis is the division of a germ cell into four sex cells (e.g. egg or sperm), each with half the number of chromosomes of the parent cell.  Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. Meiosis begins with a parent cell that is diploid, meaning it has two copies of each chromosome. Mitosis gives two nuclei, and hence two cells, while meiosis gives four. Mitosis gives identical cells to each other and to the mother cell, while meiosis leads to genetic variation due to crossing over and independent assortment. Mitosis includes one division, while meiosis includes two.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".