@Scottydamion,
Scottydamion;135001 wrote:That "negative" selection pressure is most likely the result of big brains evolving and hip size staying the same. However, even more growth occurs after the baby is born, is that growth the result of "negative selection pressure"?
That quote seems to say that hip size and brain size are both found in the same gene, or set of genes... that is why the argument makes no sense.
It is indisputable actually. If you look into the recent evolution of H Sapiens, and forbears, it is doubtlessly the case that adapting to a bipedal position and growing a large brain had very many difficult consequences for the species. As a result, the maternal mortality rate for Homo is much higher than for the great apes. So, there must have been some immediate evolutionary benefit to the emergence of bipedalism and a large forebrain.
What was it?
And on the other point you make, in fact, there are many instances where a group of changes seem to be orchestrated in order to give rise to a coherent change within the morphology of a species.
Genes can embody high level abstractions such as "do what it takes to form an eye." Pluck out the
Eyes absent gene from a mouse and insert it into the genome of a fruitfly whose
eyes absent gene is missing, and you get a fruitfly with eyes. Not mouse eyes, mind you, but fruitfly eyes, which are built along totally different lines. A mouse eye, like yours or mine, has a single lens which focuses light on the retina. A fruitfly has a compound eye, made up of thousands of lenses in tubes, like a group of tightly packed telescopes. About the only thing the eyes have in common are that they are for seeing. So, somehow, the genetic code can embody, not just sequential or linear changes in functionality, but different ways of accomplishing a purpose. So adaption indeed works in mysterious ways. [Nancy M. Bonini, Quang T. Bui, Gladys L. Gray-Board and John M. Warrick, "The Drosophila eyes absent gene directs ectopic eye formation in a pathway conserved between flies and vertebrates,"
Development (1997) 124, 4819-4826.]