marum, the giants your talking about or nephilium , are here today ! . But over the centuries they have greatly decreased in height from there forefathers like Goliath.
google this names :bao xishun ,Kareem Abdul Jabbar and Leonid Stadnik.
Even other abnormally tall people are in fact disendance of this giants in the bible ! . Why did i say they have decreased in size over generations is because from Adam ,who was perfect in every way since he was in a world with out sin. Then after his fall the life span people lived up to decreased rapidly until today you hardly hear anyone living beyond a 150 years old. This is the same with peoples bodies nowerdays. They are degenarating from one generation to the next. This days sicknesses that you had not heard 50 years ago seem to pop up from nowhere. So this giants along with there health have sadly decreased in height also.
This is all the result of sin. The bible says: "the wages of sin is death".