Background

Developmental biology: The biomedical science that studies the development and transformation of embryos(1). My topic question is when does human life begin? For centuries scientists and philosophers have struggled to answer that very question. It seems that no two views are the same. Plato contended that the human soul does not enter the body until birth. On the other hand Pythagorean stressed that the human soul was created at the time of conception. The Christian bible also states that life begins at conception, the sperm and egg come together to cause conception. Fertilization gives each organism its own genome(2). In humans a persons genome is created by combining 23 chromosomes from each contributing parent. This genome is also referred to as DNA. Some of the instructions embedded in DNA define the species. There is no scientist in the world who would tell you any living creature can reproduce any offspring of a different species.
Biology of prenatal development:
During the first 8 weeks the child referred to as an embryo- meaning "growing within." After that it is considered a fetus "unborn offspring." Human development begins at conception with the formation of a zygote. 6 days after conception the zygote- which is now a blastocyst- implants itself in the uteri an wall and begins to form two germ layers; the hypolast and epiblast. Both play a critical role in forming major body systems. At 3 weeks the brain divides into 3 sections and at 3 weeks 1 day the heart begins beating. The brain begins to function through "waves" around 6 weeks. By 7 weeks the 4-chamber heart is almost completely developed. 15 weeks after conception is when "quickening" occurs. This is when the fetus begins moving on its own. At 22 weeks their lungs gain the ability to breath air. In the 3rd trimester their is a period of rapid brain growth. Then, at 9 months the baby is full term and ready to be delivered.