What early evidence is there that pre-historic people subscribed to an informal form of religion as opposed to a formal one?

The most obvious evidence of an informal religion is that
Neanderthal man buried his dead with ceremony. Neanderthal burial sites have indicated
that the deceased was actually buried there, not simply abandoned as a dead animal.
There were often artifacts with the person, clay indicating that it may have been used
for post mortem body markings; but most importantly pollen from flowers; Neanderthal
engaged in the time honored practice of using flowers with
burials.

The peculiar system of burial which they followed
indicated rather succinctly that they had some belief in life after death; that the
person they buried would live again in some fashion. It was not a formal religion that
we know of because without any written language; there was no standard form of worship
or belief that can be determined. The best guess that can be made is that their religion
was somewhat traditional and based on custom and practice rather than on a
creed.

When early humans began settlements such as Catal
Huyuk and Jericho, there is evidence of a more formal religion, led by priests and
involving a bull-like deity. This could very well have been the forerunner of the
worship of Baal, the god of the storm, who often had bull like
features.