That may well be because there is neither scientific consensus on the matter of when human life actually begins nor agreement that it is a question that biologists can answer using their science. Scott Gilbert , the Howard A.
Schneiderman Professor of Biology emeritus at Swarthmore College, is the author of the standard textbook of developmental biology. He has identified as many as five developmental stages that, from a biological perspective, are all plausible beginning points for human life. Biology, as science knows it now, can tell these stages apart, but cannot determine at which one of these stages life begins.
The first of these stages is fertilization in the egg duct, when a zygote is formed with the full human genetic material. If genetic material alone makes a potential human being, then when we shed skin cells — as we do all the time — we are severing potential human beings.
The second plausible stage is called gastrulation, which happens about two weeks after fertilization. At that point, the embryo loses the ability to form identical twins — or triplets or more. The embryo therefore becomes a biological individual but not necessarily a human individual. Disappearance of this pattern is part of the legal standard for human death ; by symmetry, perhaps its appearance could be taken to mark the beginning of human life. The fourth possible stage, which is the one endorsed in the Roe v.
Wade decision legalizing abortion in the United States, is viability, when a fetus typically becomes viable outside the uterus with the help of available medical technology. With the technology that we have today, that stage is reached at about 24 weeks. Sign up today. Weeks 28 through 40 bring the arrival of the third trimester. Understanding a pregnancy week by week can help you make informed decisions and prepare for the big changes that lie ahead.
A new study finds that epidurals do not affect child development in their later years. A fetal arrhythmia is an irregular heart rate — too fast, too slow, or otherwise outside the norm. It's often benign. Postpartum diarrhea after a C-section is normal. Sharing our experiences of pregnancy and infant loss can help us heal.
Using breast milk for eczema is a popular home remedy. Health Conditions Discover Plan Connect. Parenthood Pregnancy Embryo vs. Fetus: Fetal Development Week-by-Week. Share on Pinterest. Embryo vs. The First 10 Weeks of Pregnancy. Week 11 and Beyond. The Takeaway. Parenthood Pregnancy Pregnancy Health. The First Trimester of Pregnancy. Placenta Delivery: What to Expect.
Read this next. Health Risks Associated with Pregnancy. Editorial team. Fetal development. Learn how your baby is conceived and how your baby develops inside the mother's womb. Week 1 to 2 The first week of pregnancy starts with the first day of a woman's menstrual period. She is not yet pregnant. During the end of the second week, an egg is released from an ovary. This is when you are most likely to conceive if you have unprotected intercourse.
Week 3 During intercourse, sperm enters the vagina after the man ejaculates. The strongest sperm will travel through the cervix the opening of the womb, or uterus , and into the fallopian tubes. A single sperm and the mother's egg cell meet in the fallopian tube. When the single sperm enters the egg, conception occurs. The combined sperm and egg is called a zygote. The zygote contains all of the genetic information DNA needed to become a baby. Half the DNA comes from the mother's egg and half from the father's sperm.
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