Human life begins at conception, which is also known as fertilization. At this point, a brand new human being is formed.
This new person has its own unique DNA and is a complete human, not just a part of one. The only thing this new person needs is the right environment to grow and develop. Even though it is small and still growing, it is a complete human being.
There is a lot of scientific evidence that supports this belief. Scientists use certain criteria to distinguish different types of cells from each other. They can also use this criteria to tell human cells apart from other kinds of cells.
A human being is made up of human cells, but it is different from just a group of cells because it has the special molecular makeup and behavior of an organism. An organism is a living being that is made up of many parts that work together in a coordinated way.
It's important to understand that the difference between a human being at the beginning of its life and an adult is only a difference in form, not nature. In other words, the human being's nature is present from the very beginning of its life, not just later on.