Originally posted by Suzianne
ummm, what "little piece of iron"? Papers such as this: http://www.ncbi.nlm.nih.gov/pubmed/20144612 have shown that the homing mechanism of Pacific salmon is olfactory in nature.
And it's well-known that the Pacific salmon and trout diverged from other salmon genera in the Miocene era, about 20 million years ago, co-existant with topological changes in had these homing mechanisms in place. I do not know how far back this homing ability goes.
I actually just watched a TV documentary on this and so far have only found this info. But I'll keep looking. Thanks.
Salmon migration: Using magnetic sense?
One of the mysteries of nature is how salmon manage to navigate in the oceans and return to spawn in the very same streams from which they came. It is known that the odor or taste of the particular stream plays a role. Salmon can home-in on the smell of “their” stream if they are sufficiently close to its mouth so that the water has not been diluted to the point where it is unidentifiable.
But how can odor play a part when the fish migrate over thousands of miles in the open ocean and cross ocean currents which destroy any possible “trail” that may lead them back? At any rate, it is known that salmon do not follow meandering paths back “home” to answer the spawning instinct, but travel directly to their spawning grounds by the most direct route when sexual maturity occurs.
What is it that points them in the right direction? Probably there is more than one homing mechanism that fish use to find their way. An olfactory “imprint” is made on smolts as they leave their home stream. This enables them to identify it by smell as they approach it later from the ocean. But to approach the stream mouth from the open sea, at least one other imprint must first be made in order for them to arrive in the general area. It has been shown that some fish are remarkably perceptive of the Sun’s azimuth and altitude, and that they are sensitive to the time of day. Under ideal conditions, this would permit a method of determining geographic north. But in a region where overcast conditions predominate (as they do in the North Pacific and Bering Sea), and because the fish swim at night and move into deeper water during the day, celestial clues are not consistently available. Therefore another means of correcting navigation is probably used. It is strongly suspected that the ability to sense the earth’s magnetic field may provide this additional method.… Extrapolating these findings to the migration process, the conjecture is that, after the salmon fry have grown to smolts and entered salt water, chemical and hormonal changes occur which imprint upon the fishes’ nervous system a “memory” of its magnetic latitude and longitude at the time that it enters the ocean.
(((There appear to be two possible ways by which the magnetic field can influence a fish’s nervous system. The first is that the ferromagnetic mineral magnetite in the creature’s brain may function as a biological compass which is ‘set’ at the time of entry into the ocean (magnetite occurs across the biologic spectrum from bacteria to dolphins). The information retained is the vertical and horizontal components of the Earth’s magnetic field at that point, and the declination of the horizontal component, which is the difference between magnetic and true north, presumably determined by the Sun. These factors taken together provide a combination that is unique for any geographic location.)))
But my question is, this is such a remarkable thing that so many life forms have but how did this just happen? At one point in this evolutionary trip for the Salmon, did they always have this ability?