Today in class, we reviewed drosophila development and continued with vertebrate development. One of the most interesting concepts that we discussed was the role of maternal and zygotic sources for development. Although we often think that vertebrates (especially mammals and humans) are more 'nurturing' and 'motherly' than invertebrates, such as the fruit fly, our preconceived notions may be false in some manners.
During development, drosophila embryos have pre-patterning from their mothers that determines much of their development and organization. So many components of the fruit fly are fixed before any fertilization or division. Although this may seem odd, it serves much evolutionary purpose in saving time in order to exploit limited food sources.
In comparison, vertebrates, especially mammals, have much less pre-patterning from their mothers that determines the organization in development. In fact, maternal influences are minimal until after the organism is born. Due to the complexity of vertebral development, it takes much longer for the embryo to grow into a full-term fetus. Therefore, it would not be evolutionarily advantageous if a human baby developed in 8 months versus 9 months so there is nothing to drive this type of evolution. However, it is very advantageous for fruit flies to develop faster in order to survive.