Ancient religions have many features in common, so much so that some scholars argue that they are merely variations on a universal human intuitive religion. The shared features include a strong emphasis on magic, particularly magic based on sympathetic connections (like influences like) and contagion (once in contact, always in contact); the concept of taboo people, places, and things; transference or expulsion of evil; connections between political and spiritual authority; ancestor worship; polytheism; focus on rituals connected to food sources, such as plants and animals; focus on the Sun and seasonal cycles, and many others. These convergent features of ancient religions occurred across many tens of thousands of miles, among human groups that have not had contact with each other for upwards of 50,000 years.
The shared features of ancient religions are somewhat connected to what is today known as "paganism", but modern paganism as recognized among post-WWII societies is quite different than the paganism of millennia ago, as it was practiced almost worldwide. The practitioners of ancient religions thoroughly believe that everyone can engage in everyday magic by performing certain rituals. One of the foremost rituals is sacrifice: regular sacrifices to keep the gods/spirits satisfied. The more grandiose, the more the gods or spirits are satiated, and the better hunt/harvest/good luck the sacrificer can expect. Rather than viewing the benefits as coming from an intermediary god or spirit, the ancients saw themselves as directly influencing the target through magic, tapping into laws built into the very structure of the universe.
Ancient religions are the ultimate in superstition and taboo. This can be observed in the traditions and habits of some of the most isolated people today, such as a few tribes in the Amazonian Rainforest, Central Africa, Southeast Asia, and Western Australia. In Central Africa, there are tribes that avoid saying thousands of words because they sound vaguely similar to the name of a dead ancestor. In the Amazonian Rainforest, the wives of warriors must engage inepetitive sympathetic rituals while their husbands are away at war, for instance sitting on the floor and bowing repeatedly in the direction of the war party for hours or days. When certain tribes in Southeast Asia are afflicted by contagious diseases, they bring around a totem to every house and then cast it into the river, ostensibly expelling evil along with it.
There are many shared features that ancient religions possess -- you only need study them. The nature of these shared features reveals interesting tendencies shared among all of humanity. Modern religions share so many features of ancient religions, it is easy to see how the former is an evolutionary descendant of the latter rather than a discontinuous jump.
