If we looked for the first evolutionary beginnings of war, would we look for fossilized nuclear weapon carrying fighter jets?
No, we would look for something not yet developed to the same extent as current species, something much more primitive, because the dynamic involved is supposed to be change via evolution, that is, being one thing then, but being another thing now.
So why, then, if we were looking for the most rudimentary essences of the evolution of religion, would we look for a pope, bishop, minister, or a church in the "fossil" record, or in any other records (why look for a fully developed human religion)?
It would seem more sensible to look for behaviors that could become full blown religious behavior (following billions or millions of years of evolutionary change, prior to full blown human religion ever developing):
"Secular religion" is, therefore, a natural way of describing ordinary human life: either as that way of life that is expressed in religion, or as that way of life in which religion is expressed. The conceptual need to reestablish the secular ramifications of what appertains to a religious order, or to a hierarchical church, or to a transcendent sacred, only proves the symbiotic relationship of the religious and the secular. Thus even a "secular" form of religion will still need its "extramural" forms of expression — if it is to be called a religion at all.(Encyclopedia of Religion and Society. emphasis added). We could say, then, that we must look for forms of expression that are, in principle, the earliest inklings of the forms of religion.
One scientist fully grasps this concept, articulating it quite clearly:
I would never have imagined that things as simple as slime molds could do a primitive version of farming.(The Scientist). That scientist used the proper term, "a primitive version" of a practice that is not the same now as it was then (billions of years ago "they" did not have John Deere tractors to "farm" with).
Likewise, the teachings of evolution would instruct us that any religion of ancestors, who lived billions of years ago, would not resemble today's human religion, or be a human religion, so why look for "fossils" of a human religion as defined in the dictionary today?
Further, the book Religion For Atheists makes the point that not all religion is theology, i.e., behavior and/or beliefs based on existence of a God or gods.
So, in that light, we can look for behaviors that are not based on theology, rather, we can look for behaviors that might constitute the beginnings of "civil religion" or secular religion.
Our search would have a focus on the behaviors of various life forms we know are ancient, yet that are available for study.
The oldest forms of organic life are microbes (see The Human Microbiome Congress), which have been on Earth for billions of years.
Let's take a look there:
In the excellent book, “The Social Amoebae,” John Tyler Bonner, an emeritus professor of ecology and evolutionary biology, describes many social abilities of amoebas including communication, group activity, and individual and group decision making. Do these raise the question of cognition in amoeba?(Social Microbes, emphasis in original). We are only looking for the "seeds" of religion, not the full grown, ripe, and developed fruits of theology.
Some of their behavior is quite extraordinary. When food is scarce, individual cells join together and form a structure that functions as if it was a multicellular animal. This slug-like creature, made of individual cells working together as one, crawls to a place with more food. There, the cells break apart, and form a new structure composed of a stalk and a fruiting body, with the appearance of a plant. The cells in the fruiting body live on by separating from the stalk and flying in the air, like a seed or spore, or attaching itself to a moving animal, to transport itself to a new place to start the colony over in a new location with the possibility of more food. The cells forming the stalk altruistically sacrificed themselves, by becoming a dying part of the structure. These amoebas, which had been living individually, came together to function as a multicellular creature to increase their access to food, then reverted back to behaving as individual organisms. The communication necessary for such actions is extraordinary.
So, since microbes exhibit altruism and community behavior for the good of all, are those "indicators, memes, or the inkling of religious behavior?":
Altruism /ˈæltruːɪzəm/ is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of selfishness.(Wikipedia, emphasis added). Another consideration is the sophisticated communication that takes place among or between microbes:
Many microbes demonstrate an elaborate language of signals which elicit a wide range of other behaviors.(Microbe Communication, emphasis added). This shows that sometimes microbes need the whole community to pull together, and they take steps to make that happen, which is potentially symbolic of religion, at least in this context.
Messages between microbes often take the form of secreted chemicals. One chemical message tells others that there is not much food in a particular location; those who “hear” it go in other directions.
Individual microbes send out signals that communicate their presence, and when a certain number have signaled they launch various group activities. This is called “quorum sensing.” For example, some colonies of bacteria light up when enough bacteria are present. Similarly, they defend each other from antibiotics, grow food together, and eat each other’s waste.
A closer look at the dynamics of microbial communication is given in the post Microbial Hermeneutics, a post which shows that microbes can discern signals, interpret signals, and make choices between/among signals, even when there are conflicting signals being sent and received.
The following video shows individual microbes sending and receiving signals to come together for a social purpose, then their coming together to form a temporary multi-cellular entity in order to further that group purpose, and finally, their carrying out of that mission to find food elsewhere so as to save the majority.
Then, after many gave their lives in the effort for the survival of the group, the survivors disband to once again become individuals following their individual single-cell pursuits.