There is a concept in Islam called the fitrah which refers to the primordial state of belief in Allah. Muslims believe all people are born Muslims, at least in the sense that the human is born with an innate knowledge of the oneness of Allah; We are simply taught something different, Christianity or Hinduism, for example, by our parents or society. Fitrah is often translated as “nature”, as in it is our nature to believe in the one God Allah.
I don’t believe we are all born Muslims. Children are not born into any religion. I view this idea as a simple attempt by organized religion to monopolize the religious tendencies of all humankind, right up to and even before birth. Perhaps the parallel would be Christianity’s claim that we are all born into sin and therefore must have an avenue for redemption. This line of reasoning cements the idea, at least in the mind of the believer, that their particular religion is the correct one; that even all of nature and the very essence of humankind somehow bows to the tenets of religion. This idea is very strong in Islam and numerous verses can be found in the Quran and hadith conforming to this concept.
As I said, I disagree with the idea that we are all born Muslims, but are we born believing in God? Rather, let’s frame the question in a more universal way. Since true monotheism is a rather new idea on the historical timeline of human religion, it doesn’t make sense to purport that we are essentially monotheistic. Yet, religion does seem to be culturally universal. Is there something in our nature, or even in our very DNA which gives us the propensity to believe? Some researchers think there is. Some articles here and here demonstrate that the human mind has a propensity to believe in God, or at least to engage in the religious experience. There are even best-selling books written about this concept such as The God Gene. Neuroscientists and psychologists like Andrew Newberg , Michael Parsinger and many others have empirically studied what happens to the human brain (namely the thalmus, parietal and temporal lobes) when engaged in some type of religious rite such as meditation or intense prayer along with changes that take place during an ecstatic religious experience.
As science is showing us, the brain does appear to be structured in a way to allow for religious experience: There seems to be a correlation between neurological changes and religious experience. In other words, our brains have evolved with an innate ability to experience religious states. And as evolutionary biologists and anthropologists have pointed out, religion does serve an adaptive purpose. In fact, research also shows that believers are better equipped to handle adverse life situations and tend to be more happy overall than their atheist counterparts.
But while all of this certainly gives us insight into truths about the human experience, the conclusions one draws from it rely heavily one’s own worldview and beliefs. The non-believer might take a very materialistic, naturalistic position and say that this evidence is further evidence that God can be explained by simple brain chemistry. That God is simply a construct of evolutionary adaptation. Conversely, the believer would interpret the evidence as proof that God exists; That God has built us with the ability to believe in him and belief is natural and intrinsically human.