Intelligence is the ability of a living entity to reconstruct patterns and sequences and events from previous remembered experience and to modify its survival behaviour advantageously. Progressively enhanced by evolution, it is a memory structure adaptation whereby an individual of a species is able to react to unusual circumstances in its immediate environment, in such a way as to foster its own survival and hence reproduction potential.
In general of course, all living things have evolved to detect and react to their environment. At a primordial biological level, adaptations to light or moisture or temperature levels involves the organism in possessing physical and physiological systems which cope with the local circumstances. If the environment changes rapidly however, as it is often likely to do, such long term evolutionary developments can be very quickly stressed to destruction. A species which has accumulated adaptations to cope with one type of climate or ecology may not survive a rapid change to a very different climate or ecology. Extinction events will tend to enhance intelligence by culling out any lack of memory structures. With the evolution of complex memory systems, living things can detect and react to their circumstances and as they learn to recognize consistencies, they then have the opportunity of developing means of exploiting the appreciation of those consistencies to enhance their survival. Intelligence is the behavioural outcome that results from the evolution of memory structures.
Intelligence shapes and is shaped by evolution. As species, symbiotic or otherwise, acquire the ability to recognize the behavioural traits of their prey or their predators, they have the potential to adopt new behaviours accordingly. The prey and predators of those species will now in their turn have to recognize the modified behaviour and modify their own behaviours or be disadvantaged.
Although shaped, developed and complexified by the aggressive natural process of recycling species phenotypes as food...the eat and be eaten phenomenon...the ability to reconstruct patterns and sequences from experience has many other applications besides that of raw survival; the creation of all forms of art; the participation in any of the diverse varieties of games; the manipulations and deceptions of social and political structures. Humour is not possible without intelligence to appreciate a set of rules and the consequent ruptured expectations. The so-called "Darwin" awards link humour, evolution and intelligence in bestowing post-mortem honour on those individuals who have removed themselves from the human gene pool by an act of sublime stupidity.
Much discussion about the nature of "intelligence" has been confused by numerous spurious assumptions. From the most extreme arrogance which assumed that humans were the only species which possess it, thru to the various unhelpful preoccupations with "problem solving", "nature vs nurture", "multiplicity of intelligences" and so on, the essential nature of the intelligence phenomenon has been obscured. Intelligence is a very general existential capacity and not to be constrained to some problem-solving ability with hypothetic scenarios.
As biological memory structures become more elaborate and increase in capacity, the fundamental recognitions of periodicities, inertial mass and sources of energy are enhanced by the more abstract simplification consistencies of number . Most species respond to the diurnal cycle for example, but only a relatively few can count. In the case of humans, one use of their intelligence capacity is to manipulate numbers to such a sophisticated degree, that their ability to modify the environment has become a significant factor for many species. As has happened at several other evolutionary crises, some species will have the intelligence, luck, or ecological indispensibility to survive with the situation and some will not.
Any attempt to create an "artificial intelligence" will need to take into consideration the intrinsic involvement of evolutionary processes, if the project is to ever reproduce the subtleties of the natural phenomenon. The automaton that can perform increasingly sophisticated tasks is not intelligent. It is simply preprogrammed. An intelligent device has to be able to detect patterns it hasn't been programmed for and initiate action that will both avoid its annihilation and transmit the information to other devices. Now that just might not be a very good idea.