Female's ability to fight pathogens

Source: 'Why we get sick'

According to this book we (including doctors) misunderstand defense mechanism against infection as disease. Author gives example fever, diarrhea and menstruation. In fact diarrhea's case is easy to spot. Some people experience diarrhea after drinking rather acidic coffee. In this situation corrective role of diarrhea is obvious.

Book dwells lot in to menstruation. According to book, menstruation liquid is tuned for fighting pathogens and is low in nutrients(so as to not to waste good things). Morphologically, female reproductive tract (F tubes, ..cervix, vagina) is not made for upstream but for down stream traffic. Only thing that defies this traffic rule is sperm, a potential carrier of pathogens. According to the book, the rate of menstruation for a species (note, not for individual) is proportional to the rate of sexual activity. Seems menstruation in other mammals is far less compared to humans because former's frequency of sex is far less compared to that of humans.

Is Natural selection looking out for us?

Source: 'Why we get Sick' book

Natural selection does not take long term well being of species in to account. Looking out for species would require 'group selection'. Example for 'group selection' is a bird choosing not to eat and thus opting for  death so that species survives. Basically the gene, actor in Natural selection cares for its well being not that of beholder. This implies that natural selection does not always result in healthy species. Richard Dawkins implies the same in his book 'Selfish Gene'.

According to this book Natural selection does not over engineer or go for perfection. We can see this in our spine. Back problem is like cough, everyone has it. According 'The aging spine' book our spine starts degenerating as early as 2nd decade.