In the reproductive process, a male sperm and a female egg provide the information required to produce another human being. Conception occurs when these cells join as the egg is fertilized. Pregnancy begins once the fertilized egg implants in the uterus. The embryo grows and becomes surrounded by structures that provide support and nourishment. Eyes, limbs, and organs appear as the embryo develops into a fetus.


Human fertilization and early development




Dr. Charles Lindemann's Lab: Sperm Facts
The human life cycle begins at fertilization, when an egg cell inside a woman and a sperm cell from a man fuse to form a one-celled zygote. Over the next few days, the single, large cell divides many times to form a hollow ball of smaller cells. On the sixth day after fertilization, this hollow ball burrows into the wall of the mother's uterus, or womb. The cells then form three layers that fold and bend into the more complex shape of an early embryo. Gradually, the cells begin to become different from one another, forming, for example, the nervous system and the circulatory system.



How Long Do Sperm Live?
Human egg fertilization marks the beginning of conception. It's when the egg or ovum is fertilized by sperm. After a sperm cell fuses with an egg cell, a new cell called a zygote is formed with the potential to develop into a new life.





Questions about the very beginning of human life continue to surface in the media, usually in the context of a public policy issue like contraceptives vs. Marco Rubio of Florida, who, in response to a question about climate change, cited it as an example of political liberals refusing to recognize long-established science about human biology. CLI is pleased to publish this slightly updated version of Dr.

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