All organisms have different adaptations for reproduction and development.
Ex: water organisms (fish and amphibians) lay their eggs in large numbers in water and wait for males to release sperm to fertilize them. This form of fertilization is External fertilization. The new organisms then develop outside the mother in the water and have little to no parental protection.
Ex: Internal fertilization (reptiles, birds) where male species inserts his sperm into the female. These female animals then lay their fertilized eggs outside of her body. The development then continues externally. This process involves laying of fewer eggs and more parental protection for their young.
Mammals also use internal fertilization and the initial stage of development (internal development) happens in the female.
Organisms who use internal fertilization and internal development release very few eggs, but the eggs are well protected.