The existing answer provides a very thorough discussion of evolution, which is actually the biological part of the question. I will address more literally the spontaneous creation part ("What was the spontaneous creation that led to this selfish gene?" - OP) and touch a bit on how the first self-replicating molecules came into existence.
Remark: Note that the authors of the quote in the OP are both theoretical physicists - indeed, the question here is more about "how life emerged" rather than "how it evolved".
Spontaneous creation is a reference to a concept known as spontaneous symmetry breaking in physics, as emergence in philosophy, and as self-organisation in chemistry. One could think of a symmetric universe as a place where chemical elements (or elementary particles) are distributed uniformly over the space, regardless of where we are or which direction we look at. (This is a simplified vision of what is understood by symmetry in physics, but it suffices for the purposes of this discussion.) Obviously, this is not what our universe looks like: patches of very dense matter, such as stars, alternate with vacuum, some parts are extremely hot and others are extremely cold, etc. Things get even more complicated when we look at highly organized dynamic matter, such as the living organisms.
All this complexity is a result of a chain of symmetry breaking events. The interactions between the particles, chemical elements, etc. make the symmetric states unstable, and so they disintegrate into the less symmetric ones. Exactly which less symmetric state is chosen is a matter of accident - e.g., a mutation defining a new direction of evolution an emergence of a new trait is accidental.
Example: particles and anti-particles
As an example: every particle has an anti-particle, so one could have expected that the world contains equal number of protons and anti-protons, as well as of electrons and positrons (anti-electrons). Yet, in practice the atoms are made of protons and electrons, and there are very few anti-atoms made of anti-protons and positrons in the universe. This is the result of a symmetry breaking event that happened some time shortly after the Big Bang, when the symmetry between the particles and the anti-particles was broken.
Example: chirality of organic molecules
As a similar but more biologically minded example, one can think of the chirality of organic molecules. When these are artificially synthesized, one usually ends up with an equal proportion of the molecules of both chiralities. Yet, only one chirality is encountered in the living organisms. This is a result of another symmetry breaking event, somewhere at the time when the first self-replicating molecules had emerged and those of one chirality, by pure chance, gave rise to living organisms, while the others were less lucky.
Emergence and evolution of micromolecules has been also analyzed as a symmetry breaking event, notably by Manfred Eigen, although this requires more abstract notion of symmetry.
Order from disorder
While it is fair to say that we understand well how symmetry breaking comes about in non-living matter (in physics and chemistry), and how evolution happens (in biology), it is not immediately obvious that the scientists agree on how the non-living matter becomes a living one. The interdisciplinary nature of the question certainly complicates it. Prigogine and co-workers believed that the dissipative structures were the answer, but Phil Anderson disagreed. Perhaps one could reproach Dawkins and his brand of militant atheism for hiding under the carpet the unanswered scientific questions, for the sake of fighting creationists (who are arguably a minority even among the religious folks.)
- Erwin Schrödinger, What is life?
- Manfred Eigen, Self-organization of matter and the evolution of biological macromolecules
- Phil Anderson, More is different; More is different - One more time
- I. Prigogine and I.Stengers, Order out of chaos: Man's new dialogue with nature, Nicolis and Prigogine Self-organization in nonequilibrium systems: From dissipative structures to order through fluctuations.
- P. Anderson and D. Stein, Broken symmetry, emergent properties, dissipative structures, life: are they related?
- Kauffman, The Origins of Order: Self-Organization and Selection in Evolution