Senses beyond sight
Reference: Sense
Electric fields, magnetic north, infrared, pressure at a distance, and sound used as a lamp. Most of the information available to living things is not visible, and the human sensory set is a narrow selection from what is on offer.
What other kinds can detect
- Echolocation — bats and toothed whales emit sound and read the returns, building a spatial picture in the dark or in murky water.
- Electroreception — sharks and rays carry the ampullae of Lorenzini, jelly-filled pores that detect the electric fields of muscle activity. A shark can find a fish motionless under sand, by its heartbeat.
- Magnetoreception — migratory birds hold a heading over thousands of kilometres. The leading account involves cryptochrome proteins in the eye, which would mean some birds see the magnetic field as a pattern laid over vision. The mechanism is still being worked out; the capability is not in doubt.
- Infrared — pit vipers, pythons and boas have facial pit organs that image body heat, giving a thermal channel alongside sight.
- Lateral line — fish read pressure changes along a row of sensors down the flank. It is touch at a distance, and it is how a school turns as one unit.
- Chemoreception — a snake’s forked tongue delivers to a paired organ in the roof of the mouth, so it smells in stereo and can follow a gradient the way we follow a sound.
The convergence that goes down to the gene
Bats and toothed whales both echolocate, and they are not close relatives — the ability arose separately in each.
What makes this the strongest convergence case in the section is that the agreement reaches the sequence. Prestin, a protein in the hair cells of the inner ear that governs high-frequency sensitivity, shows the same amino acid changes in echolocating bats and echolocating whales — changes their non-echolocating relatives do not carry. Analysed by sequence alone, the bats and the whales group together on this gene, against their own families.
That is two lineages arriving at the same molecular answer to the same problem, independently. It is either the clearest available demonstration that physics constrains biology down to the protein, or the clearest available demonstration of a reused component. The observation is the same under both readings. This app records the observation.