Clarify why a diagram of evolution looks more like a bush than a straight line.

different horse species could be alive at the same time as others. they all descended from a common ancestor.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.