Both in human beings and hen, fertilization is internal but there is a difference in further development of the zygote. Explain that difference.

Although both humans and hens experience internal fertilization where sperms meet eggs within the female reproductive tract, the subsequent developmental pathways differ fundamentally. In humans, after fertilization in the fallopian tube, the zygote undergoes cleavage while traveling toward the uterus, developing into a blastocyst that implants in the nutrient-rich uterine lining approximately 6-7 days post-fertilization. The embryo then develops entirely within the mother's uterus for approximately 9 months, receiving continuous nourishment, oxygen, and waste removal through the placenta—a specialized organ connecting maternal and fetal circulatory systems. This viviparous development strategy keeps the developing baby in a protected, temperature-controlled, optimal environment until birth.

In hens, fertilization occurs in the oviduct, but instead of implanting in the mother's body, the zygote continues down the reproductive tract while accumulating protective and nutritive layers around it. Albumen (egg white) is deposited around the developing embryo, followed by shell membranes and finally a hard calcium carbonate shell, all added as the egg moves through different oviduct regions over approximately 24-26 hours. The completed egg is then laid, and all subsequent embryonic development occurs externally during incubation, with the embryo deriving nutrients from the yolk and albumen rather than maternal blood. This oviparous strategy allows the hen to produce an egg daily without the extended reproductive commitment required by pregnancy, though it provides less protection and developmental control than internal gestation. The fundamental difference reflects evolutionary trade-offs: mammals invest heavily in fewer offspring with extended parental care, while birds can produce multiple eggs relatively quickly, though with lower individual survival rates without sufficient incubation and parental protection.