Evolution is not a chance event. It is recursive process of striving to gather and understand new information, then using this information to learn new ways to gather more information.
When thinking about evolution, avoid thinking about multicellular creatures, cells, and genes. Focus on the web of communications that creates these in context with their population and ecosystem.
Evolution happens there, in the flow of information through the web of inter-relationships between the focal points of beings. Individual creatures appear within these webs of communications as populations of billions of cells creating the appearance of multicellular creatures. Populations of millions of individual creatures intercommunicate to form sub-species and species. It's all in the flow.
The advancing evolution of perceptual abilities is driven by the need to reduce the error of expectations, to increase definition of differences in the flood of information within the webs of intercommunications, and thus improve chances of survival.
Behavior is always a response to perceived events tempered by memory of learned solutions to conceptual problems.
Each action leaves a residue in the memory of the being, and often in the sequence of information flow extending from the atomic configuration of the creature out into the complex of associations of its total environment. These changes determine the next perception and subsequent reaction.
Eons of learning new intercommunications produced pseudopodia, nematocysts, tentacles, claws, jaws, teeth, claws, hands, to satisfy the desire to survive. Creatures exist by the active process of positioning themselves in the perceived environment to intercept the required elements and energy and information to sustain the flow of information through their networks of communications.
Survival depends on the ability to acquire needed elements and energy for growth or maintenance, avoidance of predators and accidental death, and reproduction. Opportunities for survival increase in direct proportion to the strategies for differentiating finer and finer changes in the stream of energy and elements.
Coral polyps placidly extend their tentacles in Sea, inflated but inactive, until something blunders into them.
The cellular sensory systems on the tentacles, triggered by touch, tether a potential food object to the tentacle by microscopic harpoons and glue-smeared threads.
Chemical analysis by the cells forming the tentacle quickly determine if the object will provide needed materials and, if so, the tentacle folds toward the mouth (as in the photo) by the selective pulling and relaxation of muscle cells in the tentacles.
The tentacle is thrust through the centrally located mouth and the food wiped off and digested with chemicals produced by cells of the interior lining of the gut. Amoeboid cells grab the liberated phosphates, nitrates, carbohydrates and amino acids and take them to where other cells require them.
Nautilus have tentacles, but they also have eyes. The whole nautilus body reacts to visual perceptions. It actively swims in pursuit of prey it sees and away from dangers. The tentacles are always active, moving, touching, grabbing. The nautilus turns its whole body to aim its eyes in the direction awareness is most aroused. A nautilus knows what will satisfy its desire long before it is able to touch the object. It moves through Sea with determination; aware, within its horizons of perceptions, of what it wants and how to get it. Success or death moves with its awareness and perceptual accuracy.
So, too, evolution, the whole web of intercommunications, learning through the millennia, moves with determination; success or death depending on the perceptual accuracy of the beings which propel it.
Each new perceptual ability expands the horizons of perception and alters the flow of information within the entire information system. When eyes evolved, a whole new kind of awareness appeared in Sea. This changed, forever, the direction of evolution by altering the network of information from the ecosystem down through all the layers of being to the distribution of elements and sunlight.