inreproduk

Inreproduktion is a term used in some Swedish biological literature to describe reproductive processes that occur predominantly within the body of an organism, as opposed to external reproduction where fertilization or embryonic development takes place outside the parent’s body. The concept encompasses internal fertilization and the subsequent development of the embryo, which may occur inside the parent or through structures that provide nutrients during development.

Key features include internal fertilization, where male gametes are transferred directly into the female reproductive tract, and a range of developmental modes after fertilization. Development can occur entirely inside the female (viviparity), inside a laid but internally fertilized egg (ovoviviparity), or after laying eggs that hatch externally (oviparity). Internal reproduction is widespread across major animal groups, with mammals typically showing viviparity and placental connections, birds and many reptiles exhibiting internal fertilization with external egg development, and some fishes and amphibians displaying internal fertilization with varied developmental strategies.

Evolutionary significance stems from protection of gametes and embryos, more efficient fertilization, and the possibility of extended parental care. Trade-offs include higher energetic costs and longer generation times in many species.

In humans and other mammals, internal reproduction involves fertilization within the female reproductive tract, pregnancy, and birth, supported by placental or similar nutrient-transfer systems. Reproductive technologies and medical interventions have influenced contemporary outcomes of internal reproduction, including conception methods and assisted gestation.

See also external fertilization, viviparity, oviparity, placentation, marsupial reproduction.