Explaining the existence of intelligence to a Christian Apologist

A Christian apologist says...

"you are unable to account for the existence of intelligence itself on our insignificant rock revolving around a minor star"

Well, yes I am! Not just me obviously...

The existence and development of human intelligence, and intelligence in general, can be explained by biology, in particular by the processes of evolution. Intelligence is an adaptation, and partly the result of natural selection, which means it is no different to any other adaptation, such as the speed of a cheetah or the neck of a giraffe.

Much evidence comes from the great apes which provide living models of the cognitive basis from which human intelligence evolved. Many of the intellectual qualities believed to have evolved in our ancestors are recognised in the great apes and therefore originate in our common ancestor more than 6 million years ago. 

Two million years ago saw the appearance of Homo habilis which had the ability to use tools. From this species evolved Homo erectus with a dramatic enlargement in cranial size coinciding with evidence of enhanced intelligence such as task-specific tools, complex habitats, and coordinated, cooperative, long-distance hunting. The larger brain facilitates a higher resolution of memory, which enables complex associations between memories and provides the foundation for “self-triggered thought”, the rehearsal and refinement of skills, and thus the ability mentally go beyond “what is” to “what could be.” 

Another rapid increase in brain size is observed 600,000 years ago which eventually (but not immediately) led to a massive increase of human-made artifacts in the Paleolithic era (The “Stone Age”) which saw the emergence of art, science, politics, religion, and language. This sudden increase in intelligence wasn't just because of the newly evolved brain components or increased memory but was mainly due to a more sophisticated way of using memory, such as enhaced symbolic thinking, a wider and more flexible cognitive ability, and the capacity to shift between different modes of thought. This also saw the emergence of “meta-cognition” enabling our ancestors to reflect on their own nature, to learn from previous generations, record knowledge and even to override their own nature. 

That's the “how” - but then there is the question of why human intelligence evolved. There are two drivers: Biological and Cultural. 

Biologically, expressions of intelligence emerged as by products of the evolutionary mechanisms of natural selection and selection by learning ability (known as the Baldwin effect). By learning and recording knowledge, human intelligence was able to build on the previous experiences of many generations and billions of individuals, giving each new generation a “head start” (no pun intended) which is not available to other species. This gives our species a hugely significant advantage. (Memetics is also a mechanism at work in this context).

Culture provides a second, parallel form of evolution similar to the process we see in the earliest, most primitive forms of life which were self-organized and self-regenerating, and probably did not evolve through natural selection, but through the inheritance of acquired characteristics (known as the Lamarckian process). 

Richard Dawkins provides a useful overview…

"We know, for example, that an earthworm introduced into a Y-shaped glass tube with, let’s say, an electric shock on the right-hand fork and food in the lefthand fork, rapidly learns to take the left fork. Does an earthworm have consciousness if it is able after a certain number of trials invariably to know where the food is and the shock isn’t? And if an earthworm has consciousness, could a protozoan have consciousness? Many phototropic microorganisms know to go to the light. They have some kind of internal perception of where the light is, and nobody taught them that it’s good to go to the light. They had that information in their hereditary material. It’s encoded into their genes and chromosomes. Well, did God put that information there, or might it have evolved through natural selection? It is clearly good for the survival of microorganisms to know where the light is, especially the ones that photosynthesize. It is certainly good for earthworms to know where the food is. Those earthworms that can’t figure out where the food is leave few offspring. After a while the ones that survive know where the food is. Those phototropic or phototactic offspring have encoded into their genetic material how to find the light. It is not apparent that God has entered into the process. Maybe, but it’s not a compelling argument. And the general view of many, not all, neurobiologists is that consciousness is a function of the number and complexity of neuronal linkages of the architecture of the brain. Human consciousness is what happens when you get to something like 10^11 neurons and 10^14 synapses. This raises all sorts of other questions: What is consciousness like when you have 10^20 synapses or 10^30? What would such a being have to say to us any more than we would have to say to the ants? So at least it does not seem to me that the argument from consciousness, a continuum of consciousness running through the animal and plant kingdoms, proves the existence of God. We have an alternative explanation that seems to work pretty well. We don’t know the details, although work on artificial intelligence may help to clarify that. But we don’t know the details of the alternative hypothesis either. So it could hardly be said that this is compelling."

For further detail see the Cambridge Handbook of Intelligence

http://www.cambridge.org/us/academic/subjects/psychology/personality-psychology-and-individual-differences/cambridge-handbook-intelligence

With particular regard to the evolution of intelligence, you can read Chapter 17 here... 

http://arxiv.org/pdf/1308.5034v1.pdf