December 11, 2008 | David F. Coppedge

Fish and Reptiles Converge on Magnetic Navigation

Two very different kinds of animal both have outstanding ability to navigate by earth’s magnetic field: salmon and sea turtles.  A new hypothesis by scientists at University of North Carolina at Chapel Hill, published in PNAS,1 suggests that the young are “imprinted” with their local magnetic field signature at birth.

From a navigational perspective, some of the most remarkable migrations are accomplished by marine animals that begin life in particular geographic areas, migrate across vast expanses of sea, and then return as adults to their natal areas to reproduce.  How such animals navigate back to natal areas across seemingly featureless ocean, and after absences ranging in duration from a few years to a decade or more, has remained enigmatic.  In this article we propose a new, unifying hypothesis to explain natal homing in two iconic long-distance migrants, salmon and sea turtles.  Specifically, we propose that these animals imprint on the magnetic field that exists at their natal area and use this information to return to their natal region years later, close enough for local cues (olfactory in salmon, unknown in sea turtles) to guide them more precisely to their spawning or nesting sites.  This magnetic imprinting hypothesis, which focuses on the movement ecology linkage between an environmental factor (the Earth’s magnetic field) and navigational capacity, also suggests the surprising possibility that rapid, naturally occurring changes in the Earth’s field occasionally exert a strong influence on ecological processes by altering animal movements.

The article was summarized by Science Daily.  In the original paper, the authors puzzled over how and why this amazing ability evolved:

Regardless of how it is accomplished, navigating hundreds or thousands of kilometers to reproduce in a particular geographic area does not appear to be advantageous when other suitable sites for reproduction often exist along the way.  The costs of such migrations appear considerable in terms of energy expenditure, stress, and risk.  For such a pattern to evolve, the benefits must be correspondingly high.  In evolutionary terms, natal homing presumably arose because individuals that returned to their natal areas to reproduce had greater success than those that tried to reproduce elsewhere.

This says little more than that the survivors survived.  All they could think of were special conditions in the environment that led to evolutionary success.  Turtles need to lay eggs on land.  The authors suggested that only a “tiny fraction” of beaches are suitable in terms of incline, temperature, accessibility and other factors.  For salmon, the need to lay eggs in fresh water causes them to seek out streams without unsurpassable obstacles.  It seems a stretch to imagine that so few habitats would work, but they tried:

To human observers, an irrational feature of natal homing is that animals often forego reproducing in suitable nearby areas to migrate long distances to their natal sites.  For example, some sea turtles feed in areas adjacent to nesting beaches used by their own species, but nevertheless migrate long distances to nest elsewhere; similarly, salmon on their way to their own natal rivers often swim past other rivers where large populations of conspecifics spawn.  From the perspective of the animal, however, assessing the suitability of an unfamiliar area for reproduction may be very difficult.  A turtle crawling out of the sea to nest probably cannot tell that a large population of raccoons is nearby and will consume her eggs after she departs, and salmon passing by the mouth of an unfamiliar river may be unable to determine whether there are suitable spawning grounds a hundred kilometers upstream, or instead an impassible waterfall.
Under such conditions, in which suitable reproductive habitat is scarce and reproductive output can be strongly affected by factors that are difficult to assess, it is perhaps not surprising that natural selection has favored individuals that return to their natal areas to reproduce.  In effect, the very existence of an adult animal confirms that its natal area has the attributes needed for successful reproduction, an assurance that no other location can provide.

They did not ask if a salmon or turtle is capable of having a perspective or assessing anything, and they did not ask how the precision navigational ability evolved in the first place.  If some conspecifics managed to breed nearby, natural selection must have favored both long distance migration and staying near the feeding grounds.  Their hypothesis allows that changes in Earth’s magnetic field forces changes in breeding grounds.  If so, why did some species change and others stick with the old grounds?  And how did two very different kinds of animals converge on the same navigational skill?  With such puzzles to observe, they had to admit that even human animals find it “difficult to assess” such things.


1.  Lohmann, Putnam and Lohmann, “Geomagnetic imprinting: A unifying hypothesis of long-distance natal homing in salmon and sea turtles,” Proceedings of the National Academy of SciencesUSA, December 9, 2008, vol. 105, no. 49, pp. 19096-19101, doi: 10.1073/pnas.0801859105.

The hypothesis does not even begin to explain the amazing feats of these animals.  Stating that they have a “navigational capacity” says nothing about how that capacity arose; it’s like Moliere’s doctor explaining why some drugs induce sleep is due to their possessing a “dormitive virtue.”  Saying that the “very existence of an adult animal confirms” that natural selection produced this ability is absurd.  I think, therefore I am; I am, therefore natural selection produced me, I think.
    Their obfuscation continued.  “Once it arises, natal homing has important implications for population structure,” they said.  Once it arises.  OK, tell us about that.  Apparently a miracle of chance pulled it out of a hat somewhere behind a curtain.  We are asked to imagine a salmon family in a certain river figuring out the navigation game.  “Once it arises,” we are told, the rest is easy.  Now we learn that they “have evolved specializations that enhance survival in the home river.”  More miracles just occurred when you weren’t thinking.  (Hint: they were hidden behind that passive voice verb.)  Now, Mr. Darwin provides us with a self-reinforcing marketing scheme: “Such adaptations may in turn reinforce the benefits of natal homing, inasmuch as fish that return to their home streams will be better adapted to their natal sites than to other areas, and strays will also be less successful than the local fish.”  But why?  Didn’t they tell us that conspecifics do just fine without the long navigation?  Strays succeed, they said.  Is a difference in the smell of a certain faraway stream in amounts of parts per billion really so incredibly adaptive that the species will go extinct unless they escape hungry bears and leap waterfalls for miles to get there?
    Then they told us that a certain small percentage of the population strays from the original breeding ground.  OK, then why do the traditionalists still pay the cost of going all the way to great-great-great-great-great-grandfather’s home if there is a workable shortcut?  One would think natural selection would favor those who take the easy way out.
    Listen to their mythical tale of The Prodigal Salmon, with natural selection playing the heroic Father Darwin, always welcoming the stray data into his explanatory arms:

From an ecological perspective, straying from natal areas is crucial because without it, new habitat would never be colonized [so what? who cares?].  For salmon, Quinn has hypothesized that straying and homing are under genetic control [intelligent design] and are maintained in dynamic equilibrium within species and populations.  According to this [dubious] reasoning, natural selection will favor [personification] precise homing in areas where spawning sites are of consistently high quality [judgment call] year after year.  In areas where the quality of spawning sites varies greatly in different years, however, natural selection should favor [personification] females [sexism; it takes a male’s help] which produce some offspring that home and others that stray; this strategy [intelligent design] maximizes the likelihood that at least some progeny will encounter favorable areas when they return to reproduce.

This is a passive explanation, not an active one.  “An effect is seen, therefore evolution must have been the cause.”  They don’t explain how the capability originated, nor what the “genetic controls” are and how they originated.  Maybe a small fry had a mutation and couldn’t get home, they explained next.  So?  This only means that other locations can work just fine for breeding.  We’ve all seen the photos of salmon leaping up waterfalls past bears only to arrive exhausted at grandpappy’s exact stream, with just enough energy to spawn and die.  Why pay that huge cost if there are plenty of maternity wards downstream?  And why didn’t natural selection favor salmon learning to breed out in the ocean?  If that had been observed, no doubt there would be an evolutionist ready with a story about how natural selection “favored” it.
    And didn’t they say that changes in the magnetic field can alter the animals’ ability to find their natal ground?  Indeed they did.  They said that reversals could cause “considerable ecological upheaval, as mass straying brings formerly isolated populations into contact and animals unable to locate their natal sites discover and colonize new areas (which subsequent generations can locate reliably as the field stabilizes and natal homing once more becomes possible).”  Count the miracles in that sentence.  Evolutionary miracle stories are like cigarettes.  Once you start exhaling them, it’s hard to quit.
    There are more evolutionary conundrums they did not even attempt to address.  Salmon can smell their spawning waters in parts per billion, and navigate many miles, past many obstacles, to the exact spot where they were once little fry freshly hatched years ago.  Turtles can navigate flawlessly across the sea.  Just having a magnetic imprint of the ”end point” doesn’t explain how the animals can sense the earth’s field with such precision and orient themselves from point A to point B to arrive at a precise beach or stream.  Their hypothesis does not explain how they time their journey to arrive weeks later, just past high tide, ready to lay eggs.
    Another most remarkable phenomenon is that this natal homing ability is perfected in two very different orders: fish and turtles.  In evolutionary theory, the trait would either have had to be gained by some miracle in a common ancestor of fish and turtles, then selectively retained in these two genera while other species lost the ability, or else it would have had to be “learned” independently by some nebulous idea of “convergent evolution.”  Fortunately the authors spared us the repetition of that miracle term.
    Evolutionists undoubtedly think this is wonderful work.  They slap themselves on the back and laugh about the stupid creationists who employ the God-of-the-gaps fallacy, while they have used “science” to explain the world: the creative art of narrative that evolved from campfire storytelling to its present level of sophistication.  Another puzzle in nature has been tamed by the wonder-working power of a time-honored scientific theory: natural selection, that profound idea that survivors survive.  Evolution has navigated the treacherous waters of confusing observation, and spawned fresh ideas that will grow and reproduce.  Evolution has proven itself, once again, to be adaptive to changing environments.  Hard questions may cause “considerable upheaval” to the theory, but there will always be some small-fry scientists able to find new storytelling habitats to colonize so that the population endures.
    All the while they were utilizing resources that had been provided them as a gift; neither were thankful, but became vain in their imaginations, and their foolish heart was darkened.

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