I have seen this argument posed by people like Dawkins et. al, but is this actually true? Many have pointed to how complex things in nature generally come from simpler origins, but clearly, this isn't always true. For example, a watch is not as complex as a human, but is created by a humans. It is an example of a thing being created by something more complex.
You could say that the relevant cause in question is not the cause of the watch in the preceding step which in this case would be a human but the ultimate first cause of everything. But now we're just back at square one: is there an eternal first cause?
Let's suppose that there is. Is now a simple eternal first cause more likely than a complex one?
Dawkins says, and I quote, "However statistically improbable the entity you seek to explain by invoking a designer, the designer himself has got to be at least as improbable. (p113-114)"
Why does this follow? What if this complex, intelligent first cause is physically necessary? Then, it is not statistically improbable. The whole notion of statistical improbability to a potential necessary first cause seems to be a misnomer.