"Up" explains the process of an organism becoming more exactly fine-tuned to its environment once the genes have had their influence. In a quite simple scenario, it could be that the eyesight of many species becomes adapted by contact with the environment in the following way. Observation tells us that a child's fidgeting seems to include its playing around haphazardly with the focus of its eyes. When this muscle memory variation results in a clearer image, it is reasonable to conclude that this will result in the relevant meme being retained in the memory longer than those that do not result in clear images. A clearer image contains more information than an unclear image, and, therefore, more sensory experiences creating more mental associations.
For a process of learning to begin, a new-born child needs a way of haphazardly attempting new skills in order to create its very earliest behaviour that will elicit selective responses that it will be able to sense. This is provided genetically and manifested in the form of fidgeting and babbling. It is reasonable to assume that fidgeting and babbling have evolved genetically as a way of facilitating learning. They provide an individual with a first 'meme pool' in their brain - similar to the gene pool that exists in nature.
Animals that rely most on learning seem to have the greatest flexibility in their earliest behaviour. Insects feature very little learning (often just recognition of their particular local surroundings), and entirely genetically defined characteristics. Most mammals go through a period of learning (often characterised by play), but will still exhibit genetic characteristics in their behaviour (such as badgers instinctively digging for worms even without previously learning this skill).
I'd enjoyed Wired's quick coverage of the world of competitive memorizers enough to check out this guy's www presence.