What is inclusive fitness and how does it relate to the evolution of altruism?
Image by John Carleton
EVERY SUMMER thousands of tiny Vaux swifts swoop into Portland, Oregon, to spend several months feasting on flying insects during the day and roosting in the tall chimney at Chapman School at night. NW Portland is a regular vacation stopover for swifts during their annual migration from Alaska/Canada to Mexico/South America.
Historically, migrating swifts roosted in big hollow trees they found in Oregon’s old growth forests, but now, thanks to logging and urban sprawl, most of those trees are gone. In 1994, some adventurous swift scouted out new digs in the brick chimney atop Chapman Elementary School. The little birds, 4-5" ("cigars with wings"), like the rough surfaces and cracks in the bricks that give them lots of convenient toe holds, plus the chimney is big enough to accomodate between 20,000 to 40,000 birds.
The school children and their teachers welcomed the swifts in their chimney. They researched the swifts and other migratory birds, drew and painted pictures of their feathered friends, and even elected the swift as the school mascot. As the days grew colder in late September and October, students wore their coats to class so that administrators could postpone starting up the school furnace until after the swifts left the chimney to fly south. At last, the Portland Public Schools and the Audubon Society teamed up to raise grant money to stabilize the chimney for the swifts and to install a new gas heating system for the school. The renovation cost approximately ,000 (that’s not chicken feed!), and was funded by the Collins Foundation, the Metro Central Enhancement Grant Committee, and the Autzen Foundation.
Nine years have gone by, and the swifts are still summer celebrities in Portland. If you wander over to Chapman in the early evening, you’ll find a crowd of spectators sitting on a grassy bank overlooking the school. Some bring their picnic suppers, some bring champagne, many have binoculars and cameras. All ages come to watch the swifts as they congregate and prepare to call it a day. At first, there are just a few of the little birds circling the chimney, dipping close to the mouth of the chimney stack, then abruptly pulling up and flying away to repeat the cycle. As more and more birds arrive, from a distance, they look like a cloud of bees, wheeling round and round the chimney. Other birds – predators – also appear. A hawk sits on the rim of the chimney, watching, waiting, then suddenly strikes and carries off his unlucky prey. Occasionally, the tables are turned, and a gang of irate swifts attack the hawk, driving him away, at least for a short time.
The flock grows and grows until the cloud of birds turns black, and still they circle. What are they waiting for? Maybe they’re waiting for late arrivals? Maybe they are still catching insects as they fly? (Swifts eat in the air, and during their migration, sleep midair, too). Maybe they’re waiting for the air in the chimney to be the right temperature, or for the setting sunlight to fall at a certain angle? The Audubon Society has put an information kiosk in the schoolyard; perhaps it explains what finally triggers the birds’ descent.
Gradually the circling picks up speed. The birds fly several rapid last laps, and then…..Swooosh! They dive down the chimney and disappear. The sky is suddenly empty, blank. The sun is going down, too, and evening is here. Time to go home. The swifts will stay a few more weeks, until the days get shorter and the weather gets colder. Then mid-October or so, possibly when we fall back to standard time, they will fly away to winter in Mexico.
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Question by Abel N: What is inclusive fitness and how does it relate to the evolution of altruism?
How does inclusive fitness relate to selection acting on different levels of biological organization?
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One Response to What is inclusive fitness and how does it relate to the evolution of altruism?
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Inclusive fitness is a concept invented to explain the apparent paradox of how some eusocial insects (such as ants and bees) have worker castes that do not reproduce. Individual fitness is of course calculated on how many offsprings one have that survive to adulthood and reproduce. Inclusive fitness is calculated on how many relatives one raises to adulthood. It was thought that since bees and ants are more closely related to their sisters than to their own offspring (3/4 vs. 1/2), they benefit more by raising sisters rather than their own young. Inclusive fitness therefore was thought to be an answer to one of the greatest puzzles in nature of the evolution of individuals that did not reproduce. Intoxicated by the apparent success of inclusive fitness theory, the discipline of sociobiology was born in the late 1970’s and it attempted to explain all sorts of seemingly altruistic behavior in all sorts of animals. Sociobiology provoked a lot of negative reactions and rebuttals from many scientists, who pointed out that it was simply bad, overreaching science.
Since then, there have been numerous research efforts on eusocial insects, and the results are summarized in the paper below. A quote:
“The altruism of insect workers has puzzled researchers for decades. Inclusive fitness theory suggests that high relatedness has been key in promoting such altruism. Recent theory, however, indicates that the intermediate levels of relatedness found within insect societies are too low to directly cause the extreme altruism observed in many species. Instead, recent results show that workers are frequently coerced into acting altruistically. Hence, the altruism seen in many modern-day insect societies is not voluntary but enforced.”
The workers therefore did not voluntarily give up reproduction, but they were merely slaves of the queen mothers. Since bees and ants are often thought of as superorganisms. The workers are therefore analogous to the body cells of, say, a cow. The body cells, blood cells, liver cells, heart cells etc. play no role in reprouduction and yet they are vital to the survival of the cow. Reproduction is left to the testes and ovaries of the cow, just as the drones and queens are the specialists that take care of reproduction in an insect colony. Viewed in this light, it is therefore no surprise that eusociality evolved, even in termites in which there is no inclusive fitness advantage for the workers. All that it needs for eusociality to occur is for the queen to evolve ways to enslave its daughters.
http://www.santafe.edu/~bowles/Dominance/Papers/RatnieksWenseleers2008.pdf
Cal King
November 16, 2012 at 10:52 pm