What Embryology and Science textbooks say about the Beginning of Human Beings

"Just the Facts, Ma'am": It's too bad Sergeant Friday isn't around to help us with the embryonic stem cell debate. by Clark Forsythe, AUL Much of the public promotion for human embryonic research rests on the assumption that the human embryo is not a human being. As a May 2004 letter to USA Today put it (inaccurately), "a gamete about the size of a period at the end of a sentence" is not a human being. [True, a gamete (sex cell, egg or sperm) is not a human being. But the target of embryo research is not gametes; it's embryos.] Here's a reveiw of what contemporary embryology and biology texts say about the beginning of human beings. William Larsen in his 1993 text, Human Embryology, states: "the nuclei of the male and female gametes unite, resulting in the formation of a zygote containing a single diploid [having the full complement of chromosomes] nucleus. Embryonic development is considered to begin at this point." Larsen also states that " the moment of zygote formation may be taken as the beginning or zero time point of embryonic development." Bruce Carlson in his 1994 text, Human Embryology and Developmental Biology, states that "through the mingling of maternal and paternal chromosomes, the zygote is a genetically unique product of chromosomal reassortment." Carlson states that when "the maternal and paternal chromosomes…become organized around the mitotic spindle in preparation for an ordinary mitotic division…the process of fertilization can be said to be complete and the fertilized egg is called a zygote." The one-celled human zygote is properly called an embryo. What is the nature of this...

Human Development in utero

For more photos and information about development, visit http://www.secondlookproject.org/tslp_fetal.html   Fertilization: The sperm joins with the ovum (egg) to form one cell — the zygote. This one cell contains the complex genetic blueprint for every detail   of human development: the child’s sex, hair and eye color, height, skin tone, etc. First Month   This first cell, the zygote, divides within about 10 hours and then cell division continues in an orderly fashion every few hours as the small group of cells travels down the Fallopian tube to the uterus, where the uterine lining has been prepared for implantation. There are over 100 cells already present when this tiny human embryo (blastocyst) reaches the uterus 7-10 days after fertilization. Upon implantation, complex connections between the mother and the embryo develop to form the placenta.   Benchmark Dates: Day 18 – blood vessels and the heart begin to form Day 20 – foundations of the brain, spinal cord, and nervous system are already established Day 25– the heart begins to pulsate and will continue until this person dies; the digestive system and parts of the eyes are forming Day 28 – the backbone and the rest of the skeleton (cartilage now) and muscles are forming; arm and leg buds are present and elongating At one month old, the embryo is 10,000 times larger than the original microscopic fertilized egg, and is developing rapidly. The heart is pumping increased quantities of blood through the circulatory system. The placenta forms a unique barrier that keeps the mother’s blood separate while allowing food and oxygen to pass to the developing human embryo. The word "embryo"...