How can fossils be used to determine a relationship between living species and extinct ones?

Fossils are significant in showing the evolution of species. Fossils can be used to determine features that are shared between the current living organisms and ancient organism which they are related. This can be used to study how organisms evolve and how this is related to the ecological conditions of the time compared to now. Organisms evolve so they can adapt to a changing habitat.  

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."