We have lots of different senses, including a sense of balance, heat, pain, and the ability to sense the position of our limbs (called ‘proprioception’). But if we consider the five classic senses, then taste is the oldest by a wide margin. Taste is really just the ability to detect particular chemicals in your immediate environment, and ocean-dwelling bacteria were sensing nearby nutrients and swimming towards them at least two billion years ago.
Sight, or at least the ability to detect light, was another bacterial invention, but true image-forming eyes didn’t evolve until multicellular animals appeared around 570 million years ago. By then, many single-celled organisms had also evolved the ability to sense touch. Smell normally means the ability to detect chemicals carried in the air, so this sense had to wait around another 70 million years for the first land animals to emerge.
Hearing in air came last, because sound waves are weak compared to electromagnetic waves such as light, and require specialised structures to amplify the signal, especially for high frequencies.
Fully-functioning ears didn’t evolve until 275 million years ago. But in 2015, Danish researchers suggested that lungfish may have had a rudimentary sense of hearing. These fish were probably the earliest vertebrates to start making forays onto land, around 375 million years ago, using their fins to ‘walk’ from one shallow pond to another. The study suggests that they could detect low-frequency sounds in the air via vibrations of their head, giving them an early forerunner of what eventually evolved in land animals to become the middle ear and eardrum.