Human fertilization is the union of a human egg and sperm, occurring primarily in the ampulla of the fallopian tube. The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the nineteenth century. The process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization. Various exceptions to this sequence are possible, including artificial insemination, in vitro fertilization, external ejaculation without copulation, or copulation shortly after ovulation. Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer shell called the zona pellucida of the egg. The sperm plasma then fuses with the egg's plasma membrane, triggering the sperm head to disconnect from its flagellum as the egg travels down the Fallopian tube to reach the uterus. In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro. History In Antiquity, Aristotle depicted the formation of new individuals occurring through fusion of male and female fluids, with form and function emerging gradually, in a mode called by him as epigenetic. He proposed that during conception the female supplied the material, or the body, while the male provided the soul. Galen argued that during conception the male and the female both produced a seed. However, the male seed was thicker and more powerful than the female seed because it had a natural heat that the female seed lacked. Hippocrates theorized that fertilization occurred when the male and female seed came together, and the sex of the child would be determined by the strength of the seed. If both parents had strong seed, the child would be male. If both parents had weak seed the child would be female. If one parent produced strong seed and the other produced weak seed, the more numerous type of sperm would determine the sex. Hippocrates did not assign the production of strong or weak seed to a specific sex; both males and females could produce strong or weak seed. Sperm and oocyte meet Ampulla Fertilization occurs in the ampulla of the Fallopian tube, the section that curves around the ovary. Capacitated sperm are attracted to progesterone, which is secreted from the cumulus cells surrounding the