Dziuk in Illinois has drawn attention to the
intensely competitive environment within
the uterus of the fetuses in polytocous
species (Dziuk, 1992). He makes an analogy
with the overproduction of fruits on a peach
tree or of peas in a pod relative to the eventual
ability of the parent to support the offspring.
As the fetus develops it establishes
not only its placenta but also priority for a
circulatory system and liver. These early
structures reflect the need to collect, process
and distribute nutrients and oxygen to all
the developing structures and to excrete
waste products.