Assignment: Navigate through murky water for 2800 km in the open ocean and get to a target beach in a narrow window of time. You can only go 150 km per day. Oh, and only use the senses built into your body. Mission impossible for a Navy Seal? Not for another kind of seal that does this routinely.
Bodies and Behaviors
Darwin’s theory must account for not only bodies but behaviors. The most stunning behaviors in the animal kingdom include long-distance navigation and migration. Natural selection tries to account for “complex programmed behaviors” (CPBs), but there’s an elephant in the room — an elephant seal, that is. You’ve heard about salmon, whales, and sea turtles. Now learn what the obese, clumsy-looking elephant seal with the long nose accomplishes navigation-wise. It’s an “astonishing navigational feat,” says Roxanne Beltran from the Department of Ecology and Evolutionary Biology, University of California Santa Cruz, with six colleagues, publishing in Current Biology.
Many marine animals migrate between foraging areas and reproductive sites, often timing the return migration with extreme precision. In theory, the decision to return should reflect energy acquisition at foraging areas, energetic costs associated with transit, and timing arrival for successful reproduction. For long-distance migrations to be successful, animals must integrate ‘map’ information to assess where they are relative to their reproductive site as well as ‘calendar’ information to know when to initiate the return migration given their distance from home. Elephant seals, Mirounga angustirostris, migrate thousands of kilometers from reproductive sites to open ocean foraging areas (Figure 1A), yet return within a narrow window of time to specific beaches. Each year, pregnant female elephant seals undertake a ∼240-day, 10,000 km foraging migration across the Northeast Pacific Ocean before returning to their breeding beaches, where they give birth 5 days after arriving. We found that the seals’ abilities to adjust the timing of their return migration is based on the perception of space and time, which further elucidates the mechanisms behind their astonishing navigational feats. [Emphasis added.]
Using satellite tags and time-depth recorders, the UCSC team tracked 108 female elephant seals over a decade. They observed an amazing ability: each animal independently knew when to begin its annual return based on how far it had to go. A “map sense” is familiar to us. Even without looking outside, we know about how much time to allow for a trip of 100 miles on an interstate highway. How do elephant seals do it?
Turnaround dates depended strongly on distance from the breeding beach, but were unrelated to body condition determined by vertical velocity during drift dives. Seals that foraged farther began their inbound migration earlier. These data provide evidence that seals know their distance from the breeding beach and allocate extra time to get back if they have farther to travel. It also provides an understanding of how population-level reproductive synchrony is possible for migratory animals.
“Population-level reproductive synchrony” means that they all arrived together at the target beach, no matter how far they had to swim. The map in the paper shows departure spots all along the Pacific coast as far as the tip of the Aleutian Islands. Some seals began far out in the open Pacific, and others were much closer to the coast. Unlike migrating birds, seals do not travel in groups and are unable to follow one another.
Elephant seals return to the same beaches year after year with minimal variation in migration arrival and departure date across individuals (Figure 1B). However, this consistency is not a result of group travel or active coordination because seals forage independently, and it is unknown which cue causes female elephant seals to begin their return migration months prior to giving birth at the breeding beach. The animals have vast distributions at sea, across longitudes and latitudes with dramatically different celestial cues and daylengths yet return to their beaches a few days before birth.
Reminiscent of Sea Turtles
The elephant seals’ astonishing synchrony is reminiscent of sea turtles which also coordinate their arrivals; recall scenes of female turtles all climbing onto their natal beaches together after long voyages. But sea turtles are reptiles and elephant seals are mammals. How do the researchers explain this? Wisely, they avoided any discussion of evolution.
Despite extensive research into how migratory animals pursue foraging patches in terrestrial and marine ecosystems, there has been substantial uncertainty in the when and why of movement decisions made by wild animals. We found that elephant seals show a great deal of variability in when and where they begin their multi-week return migration (Figure 1B) based on their real-time distance from the breeding beach. While the sensory basis of elephant seals’ ability to assess their position (e.g. geomagnetic, celestial, acoustic, or olfactory) remains unknown, our data suggest that elephant seals have a map sense, which allows them to adjust their movement based on their current position relative to their destination.
No Breeding and No Survival
Giving a natural wonder a label like “map sense” evokes mental images but falls short of explanation. What is this map sense made of? Where is it located? What are its inputs? How is it coded in genes, and how is it inherited? In Illustra Media’s documentary Living Waters, the suggestion was made that sea turtles record geomagnetic waypoints on their outward journeys and retrace them on the way back. It’s not clear that is happening in the elephant seal case. The authors’ map in Figure 1 shows individual seals taking erratic paths on their return journeys. For the map sense to work, this implies that the animal keeps continuous track of the remaining distance, its bearing, and the time remaining to reach the rendezvous. Without all the ingredients of a map sense working simultaneously, there would be no breeding and no survival of the species. How could such a thing evolve by the accumulation of slow, gradual variations?
From his career expertise in navigation systems, Eric Cassell describes the requirements for map navigation in his excellent book Animal Algorithms. “This ability is especially impressive,” he says, because animals with this ability can be displaced from their location and still find their way to the destination. The human invention of GPS makes this commonplace now; our phones tell us where we are and each turn to take. For millennia before us, though, it was quite a challenge. Cassell relates some of the struggles human travelers with their large brains encountered trying to figure out their latitude and longitude on long-distance voyages. And yet a true map sense has been found in birds, lobsters, mollusks, sea turtles, and now, elephant seals, too. None of these are related by evolutionary common descent. The authors spare us the usual invocation of “convergent evolution.”
Elephant Seal Seals the Deal
Even more impressive, Cassell continues, is the cognitive sense to compute the track between location and destination. Because long-distance navigation requires computing a great-circle route on a curved planet, the animal must also be able to utilize spherical trigonometry (pp. 52-53). Add to that the requirement to make continuous corrections to stay on track, and map navigation’s impressiveness really takes on spectacular dimensions.
After six chapters of examples of natural wonders that defy evolution, Cassell presents the case for intelligent design. Then he devotes a final chapter to answering objections to the design inference. With intelligent design scoring 100 percent on its ability to explain 11 aspects of complex programmed behaviors (Fig. 7.1, p. 169), and Darwinian evolution scoring 27 percent, it’s really no contest.