Evolution News and Views (ENV) provides original reporting and analysis about the debate over intelligent design and evolution, including breaking news about scientific research.

Evolution News and Views
Evolution NEWS

Shark Knows with Its Nose Where It Goes in the Dark


As Illustra Media showed in Living Waters by taking viewers inside the nose of a salmon, the olfactory (smell) organs of fishes are stupefyingly complex. A mainframe computer network could hardly surpass the computing power packed into the tiny space of a fish nostril. Similar complexity has been demonstrated recently in cartilaginous fish such as sharks, which would only be distantly related to bony fish in the evolutionary scheme.

"The ability of sharks to navigate the vast and seemingly featureless ocean has been a mystery," Traci Watson writes for National Geographic. Michael Casey agrees at Fox News, "One of the great mysteries with sharks has been how they manage to navigate a straight path between distant locations in the ocean." They're commenting on a "tantalizing clue" that emerged from recent experiments with sharks by the Scripps Institution of Oceanography. A news item from PLOS ONE explains what the scientists did:

Little is understood about how sharks navigate straight paths between distant sites in the ocean. The authors of this study used shoreward navigation by leopard sharks to test whether olfaction contributes to ocean navigation. About 25 leopard sharks were captured alongshore. About half had their sense of smell temporarily impaired, and then they were transported 9 km offshore, released, and acoustically tracked for approximately four hours each. [Emphasis added.]

The sharks with unhindered noses came back like the proverbial cat, 62.7 percent closer to shore than the nose-plugged sharks (37.2 percent). Significantly, the impaired sharks took more tortuous paths. Live Science quotes one of the researchers:

"We basically kidnapped these sharks from their home and confused them for an hour on the way out," said study lead researcher Andrew Nosal, a postdoctoral researcher at the Scripps Institution of Oceanography and the Birch Aquarium in California. "Yet, within 30 minutes of being released in the middle of the ocean -- a place that they had probably never been -- they [those without nose plugs] knew exactly where shore was, which was really neat."

Now that we see the overall result, how does the shark do it? What equipment is required? The open-access paper in PLOS ONE doesn't say. But it does describe how olfactory expertise is widespread in the animal kingdom:

Relatively little consideration has been given to chemical cues guiding animals through the pelagic environment, even though this dynamic three-dimensional medium in many ways resembles the dynamic three-dimensional atmosphere, where chemosensory modalities are widely accepted to participate in bird and insect navigation. Evidence for olfaction-mediated homing and navigation in fishes had heretofore been limited to salmonid fishes, rockfishes, and fish larvae, operating mostly in nearshore environments. Even the most recent work, which demonstrated olfaction-mediated homing in juvenile sharks, was conducted wholly within a shallow bay. Although olfaction has also been hypothesized to contribute to pelagic navigation in sharks, this had never been tested until now.

None of the five articles says anything about evolution, either. How could they? The scientists or reporters are faced with two major Darwinian dilemmas.

First, they would have to explain the irreducible complexity of olfaction. As shown in Living Waters, olfaction is composed of numerous systems that must work together as a unit. The cilia on the olfactory sensory neurons need receptors for odorants that fit like a glove. Each neuron must respond to an odorant with a complex cascade of signals, including gene-expression feedback loops and electrical currents that travel down the axons of the cell. The signals need to know where to go: to particular points on the olfactory bulb.

The olfactory bulb (shown in the animation) is a fantastic sorting device, that takes the incoming signals from millions of neurons, measures their strength, number and time delays, and reduces all that information into a combinatorial code. That information must then target specific parts of the fish's brain, where the information must be understood and recognized by the animal. The information will only be useful, though, if the fish has a way to incorporate it into a map sense, so it knows where it is and where it needs to go. Finally, the fish needs to have software to know what to do with the information: change direction, hunt prey, flee a predator, or perform whatever other action is appropriate. That software, in turn, must tie into muscles and nerves that can produce the appropriate behavior rapidly.

Second, the evolutionist would have to explain how this amazing ability evolved in insects, birds, and two groups of fish (bony fish and cartilaginous fish). "Convergent evolution" is not an answer. It's a phrase hiding the lack of an answer. If by some miracle you could imagine one animal arriving at olfaction and the ability to navigate with it, it strains credibility to expect it to evolve independently multiple times.

Adding to the challenge for Darwinian processes to explain this is the fact that sharks (like salmon and the other animals), can supplement olfaction with other senses that are just as complex: hearing, vision, and sensing the Earth's magnetic field.

Another interesting observation was that shortly after crossing back over the continental shelf, some sharks, even after swimming for hours at relatively constant depths, suddenly and deliberately dove to the benthos, as if they were confident a bottom of suitable depth was there (S3 Fig). Surely the sharks could not see the bottom from 50 m above it, but the 'soundscape' may be fundamentally different over the shallow shelf compared to deeper offshore areas. Lastly, geomagnetic cues are strongly suspected to play a role in shark navigation and these may very well contribute to shoreward navigation by leopard sharks. In short, olfaction plays a role in pelagic navigation, but is apparently supplemented by other sensory modalities, warranting further work to elucidate how these are integrated and organized hierarchically for navigation.

If an alien intelligence visited Earth and found only sharks with abilities like these, it would be justified in inferring an intelligent cause for them. How much more when thousands of other examples in the plant and animal worlds, to say nothing of the human body, are abundantly on display? The navigation of a monarch butterfly for 3,000 miles to the exact tree its grandparents knew (Metamorphosis), the flight of the Arctic tern from pole to pole (Flight: The Genius of Birds), and fish navigation are just a taste of what's out there to study.

All one has to do is look at any creature, even a single cell, in detail. As Paul Nelson says at the conclusion of Living Waters,

I want to understand the world. I want knowledge. I want to know what's true about the world; and the assumption that living things are not random assemblages but that there's a rational logic underlying them -- that assumption is enormously fruitful for gaining knowledge. And if it's knowledge that you want, that's the direction you should go. All you need is an open heart, open eyes, and an open mind, and that signal of design that's there in nature it will be clear to you. Unmistakably. It's everywhere."

What we have is a super-abundance of evidence for intelligent design. These systems rule out blind, unguided processes of natural selection. The authors of these articles did not need Darwinian theory to add to our understanding of animal navigation, or they would have mentioned it.

Image: Leopard shark, by Kyle McBurnie via PLOS.