How do single-celled organisms reproduce

Hemoglobin is the compound in red blood cells that carries oxygen to the body. the distribution of hemoglobin in women in g/dl of blood is approximately normally distributed with mean 14 and standard deviation 1. too little hemoglobin, and you're anemic. 2. too much, and (unless you live at high altitudes), you can have other problems.

In general, characteristics that an organism survive and reproduce become more common over time. what mechanism of evolution causes this?

2. which is the last step in the scientific method?