These days it may seem like people are abandoning religion to the fundamentalists, but they're not. Religion has been around forever, and it's not likely going anywhere soon.
In fact, the story of human religion begins before humans as we know them even existed. We've found Neanderthal caves with circular stone altars dating to 176 thousand years ago, which means religious expression is pre–Homo sapiens. Around 40 thousand years ago, we start seeing mythogramic caves in which our earliest ancestors made paintings that can be considered scripture. They initially painted mysterious dots, followed by palm prints, animals, and, around 18000 BCE, the first depiction of a god — The Lord of Beasts. This is where author, scholar, and multimedia force Reza Aslan begins his slim, yet ambitious book God: A Human History. It's the story of how humans have created God with a capital G, and it's thoroughly mind-blowing.
Aslan's God is the latest addition to the genre of popular God books — Karen Armstrong's A History of God, Thomas Römer's The Invention of God, and Jack Miles's God: A Biography, to name a few. Why do we need another? While each has its own benefits, and drawbacks, Aslan's contribution is unique. For one thing, his writing is inarguably kick-ass, and so his God is simply much more pleasurable to read. Then there's his slant, with his book being "a history of how we have humanized God," a demonstration of our compulsion to project human attributes onto the divine. As he writes in the introduction, "it is we who have fashioned God in our image, not the other way around." Finally it's the vast scope Aslan wraps around the subject, staging the story with archeological evidence from our pre-historical religious past, and other modern scientific perspectives on religion as a set of human activities.
In order to understand how religion developed in the first place, Aslan explores the theories of Edward Burnett Tylor, Max Müller, Émile Durkheim, Sigmund Freud, and Carl G. Jung. These thinkers wondered if the religious impulse was evolutionarily beneficial or if it had a unique moral effect on society. Aslan dismisses their conclusions, and examines more recent theories, like the idea of a Hypersensitive Agency Detection Device (HADD, named by cognitive scientist Justin Barrett), a deep biological process that causes us to assume human agency behind any unexplained event, and which basically says that religion is foremost a neurological phenomenon. Then there's the theory of mind, by which philosophers and cognitive scientists attempt to explain our ability to think of others in the same terms as we think of ourselves.
Some of these scientists think such theories account for the origin of the religious impulse, but Aslan points out they don't explain why early humans believed they had a soul in the first place. For him, the origin of the religious impulse is "the result of something far more primal and difficult to explain: our ingrained intuitive, and wholly experiential belief that we are, whatever else we are, embodied souls." And so he takes us far back into our religious history — all the way to Eden.
Referred to as "the Temple of Eden," Göbekli Tepe is a temple complex on a hilltop near Urfa, in modern Turkey. It was built at the end of the last Ice Age, between 14 thousand and 12 thousand years ago — at least six thousand years before Stonehenge, and seven thousand before the first Egyptian pyramid. Seriously old. So old it predates the development of agriculture and the birth of civilization. This leads Aslan to write that agriculture didn't cause humans to settle into cities, where they developed art and technology. Turning this widely accepted idea on its head, he says that devotional sites such as the Göbekli Tepe indicate that the transition from the Paleolithic to the Neolithic era was rather due to the birth of organized religion.
From there Aslan shoots through time to the emergence of manism, the ancestor worship that began around 8000 BCE, and to the birth of polytheism in Mesopotamian Sumer. The invention of writing seems to have occurred in Sumerian city of Uruk around 4500 BCE, and by 2600 BCE humans could write down what gods were like for the first time. Demonstrating Aslan's main idea — that humans have always had a "compulsion to humanize the divine" — the gods (ilu) the Sumerians described were quite human-like:
The gods of Sumer were born to mothers who suckled them when they were young. They had fathers with whom they clashed as they grew older. They fell in love and got married. They had sex and birthed children. They lived in houses with their families and had relatives with whom they formed giant celestial clans. They ate and drank and complained about work. They argued and fought with one another.
The Mesopotamians eventually worshipped a pantheon of more than three thousand deities, with idols for each. Similar developments occurred in Egypt, India, and Greece, where gods were always described in human terms. They fought over petty jealousies, had family problems, displayed good and bad moods, and "could be all-knowing or just plain stupid."
Some of these religious systems can be described as monolatry, the worship of one god with acknowledgment that many other gods exist. Yet the dominant form of spiritual expression under ancient monarchies was henotheism, the belief that "one all-powerful, all-encompassing 'High God' who acted as the chief deity over a pantheon of lower gods who were equally worthy of worship." Monotheism, in contrast, is "the sole worship of one god and the negation of all other gods."
The first time such a thing occurred was in Egypt around 1353 BCE, when Akhenaten raised the sun god Aten to the status of sole god. To enforce his monotheistic religion, Akhenaten released "nothing short of a pogrom against the gods of Egypt," with armies marching from city to city, smashing the idols of other gods, and even erasing their names from documents. Yet when Akhenaten died, his monotheistic movement died with him. We still have no evidence to suggest where Akhenaten got his notion of monotheism.
Sometime between 1500 and 500 BCE (Aslan settles on 1100 BCE), an Iranian priest named Zarathustra Spitama became the world's first prophet when he received revelations from Ahura Mazda, a term that means "the Wise Lord," but refers to a god with no name, since he was the sole god of the universe. Zarathustra was the first to promote a dualistic, heaven-and-hell theology, and to reduce other divinities to "angels" and "demons." Yet the monotheism of Zoroastrianism was short lived. It was revived in the sixth century BCE, but the magi of Cyrus the Great transformed the one god into two — one good and one evil.
The Israelites had arrived on the scene around 1200 BCE, and the Bible doesn't hide that early Hebrews incorrigibly worshipped other gods, such as Baal and the goddesses Asherah, Anat, and Astarte. These are clan members of El, the chief god of the Canaanite pantheon, who, Aslan writes, "was often depicted as a bull or calf." But no — symbols of bovine animals in ancient Near Eastern religion were inflexibly systematic. Goddesses were depicted as cows. El, the father god, was only depicted as a bull. (He'd be insulted if depicted as a calf!) There was a god, however, who was often symbolized with a calf, and his name is Yahweh.
The Bible uses several names to refer to God, the main two being Elohim, which, despite being a plural form, is usually translated simply as "God," and YHWH, which is traditionally read as Adonai and translated as "LORD." In Genesis 4:1, Eve says she has "gained a male child with the help of YHWH,"  implying that the name was known from the beginning. But officially, Yahweh first revealed his name to Moses in Exodus 3:15, claiming he was the god of Abraham, Isaac, and Jacob, to whom he was known as El Shadday. Most believers understand these different names refer to the same god. There are two possible places in the Bible, however, where it appears Yahweh is not only distinct from Elohim, but also inferior to him: Psalm 82 and Deuteronomy 32:7-9. 
Two exceptions hardly seem enough basis for a definitive claim. And yet Aslan writes with full confidence that "the fact of the matter is that these biblical patriarchs [Noah, Abraham, Isaac, and Jacob] did not worship a Midianite desert deity called Yahweh. They worshipped an altogether different god — a Canaanite deity they knew as El." That is to say, Yahweh is not Elohim. The God of Genesis is not the God of Exodus. Aslan continues: "Scholars have known for centuries that there were two distinct deities worshipped by the Israelites in the Bible, each with a different name, different origin, and different traits." And yes, some scholars have certainly argued this, but others find the testimony in the Bible at best oblique. The same text can be read in different ways; rather than refer to two separate gods, the different names can be understood to represent contradictory aspects of the same divinity. We don't really know, but Aslan's decisiveness does make for a better story. And as he's proven in Zealot and even more here, he's certainly a great storyteller.
The crux of his whole narrative in God is quite simple:
The story of how monotheism — after centuries of failure and rejection — finally and permanently took root in human spirituality begins with the story of how the god of Abraham, El, and the god of Moses, Yahweh, gradually merged to become the sole, singular deity that we now know as God.
And while academics might think this problematic, it would be great if we could read the subtext of the Hebrew Bible as the story of a Yahweh's usurpation of El's position as the High God of the Divine Council, like a celestial Game of Thrones. It's the last thing the authors and editors of the Bible want us to think, but it has a satisfying explanatory power.
In any case, Aslan is right that monotheism as we know it only solidified during the Babylonian Exile. Perhaps surprisingly, the first expression of unambiguous monotheism in the Bible occurs in Isaiah 44:6, from the second part of the Book of Isaiah, otherwise known as Deutero-Isaiah, which was composed after the fall of Jerusalem, in 587 BCE. Here Yahweh declares, "I am the first and the last; besides me there are no gods." It's not that he is greatest among gods, but there are no other gods. Finally, after thousands of years and two misfires, we have true monotheism. But about five hundred years later, this extraordinary development in the history of religion was "overturned [...] by an upstart sect of apocalyptic Jews calling themselves Christians." Whether you like it or not, you've got to admit that Aslan has style.
With the idea of Jesus being God made flesh, early Christians had to account for some pretty tricky theology. How can God be both Jesus and God? Moreover, how can Yahweh — the jealous deity who gleefully calls for the slaughter of anyone who fails to worship him — be the same God of love and forgiveness who Jesus calls Father? Around the time the Gospel of John was being written, 100 CE, Marcion proposed a two-god theory known as ditheism. There must be two gods: the cruel creator God of the Hebrew Bible known as Yahweh, and the loving, merciful God who has always existed but revealed himself to the world for the first time in the form of Jesus the Christ.  We know that ditheism was eventually rejected in favor of Trinitarianism, and God became Three. Tertullian coined the word Trinity, and the Fathers of the Church clarified the matter: God is the Father, Son, and Holy Spirit, each of which existed at the beginning of time and share the same measure of divinity. Finally, things seemed to be all wrapped up.
But no. In seventh century Arabia, a 40-year-old shepherd turned merchant turned prophet named Muhammad received revelations from a god he called Allah, the only ancient Arabian god who seems to have never been represented by an idol. Muhammad identified this god with Yahweh and Elohim, saying it was really Allah all along. He devoted the rest of his life to replacing Zoroastrian dualism and Christian trinitarianism with the "Jewish view of God as One," thereby making Islam the culmination of monotheism. Aslan closes the story with the Sufis and their pantheistic conception of God: interpenetrating the universe, God is all, and all is God. But then Aslan pushes it further by saying that since we project our humanity onto God, we are God. Each one of us.
This is in the last chapter, which abruptly shifts from theological history to didacticism. Aslan tells us we need to "recognize the divinity of the world and every being in it and respond to everyone and everything as though they were God — because they are." Okay, sure. But isn't one implication of the idea that we are all God the fact that God doesn't really exist? By trying to understand and explain what God is, has Aslan come to negate God?
Throughout the book, in fact, Aslan argues that we have "humanized the divine." We have "come up with" and "devised" the pantheon of gods, "giving" them various human attributes, and we have created God in our image. While that may be true, this perspective precludes the possibility that gods like Yahweh and other divine beings have an independent existence — apart from the projections of humans. That is to say, Aslan's idea essentially negates the religious beliefs of every traditional culture in the world. Since, by his own account, he's a believer, I'm sure Aslan wants to understand the beliefs of others, not dismiss them, and yet, ironically, that's what he does in God. God, as a character, is presented in the Bible and the Qur'an as a being, not a vague divinity, so to argue otherwise is to negate both how he's presented in these books, as well as how many communities of faith have thought of God.
Aslan doesn't negate divinity, however. In fact, by presenting the perhaps paradoxical idea that humans are God, Aslan is pointing to a crucial belief in contemporary spirituality, which is that whether one believes or disbelieves in God or any divine being is less important than acting kindly, compassionately, and otherwise divinely. And one way to do that, he suggests, is to appreciate the divinity in each other.
 I'm not going to get into the theory of sources — J, E, P, and D — which account for the different use of divine names, as well as the contradictions and repetitions in the Bible, but there are several books on the subject; recommended is Richard Elliot Friedman's Who Wrote the Bible?.
 Without "corrections," namely in the Dead Sea Scrolls of the Qumran community and the Septuagint, Psalm 82 reads: "YHWH is standing in the Council of El among the gods, pronouncing judgment." Here YHWH is one of many gods in El's court; he's standing, rather than sitting on a throne, which also implies a secondary role. Deuteronomy 32:8-9 describes how El divided the nations of men among the sons of god, allotting YHWH the people of Israel.
 The Gnostics, too, were also dithesist, differentiating between the God of the Hebrew Bible and the God of Jesus. Gnostics didn't believe Yahweh was the creator of the world. Rather they believed creation was the work of a lesser god, a demiurge, who was "a deformed and imperfect deity who foolishly believed himself to be the only god in the universe." They believed this demiurge was responsible for the bungling of creation and the flood and everything messed up, not Yahweh. To me, it's pretty obvious that Yahweh is the demiurge. Though I've never heard anyone else say that.