What led darwin to believe that organisms originate from a common ancestor?

The fact that there were many different variations of traits of the finches on the Galapagos islands. He also realized this with the evidence with animals who share the same trait but allegedly gain no benefit from them.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.