Handicap principle

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Courting male peacock : The tail feathers are a hindrance when fleeing from predators.

The handicap principle is a theory of social signals that includes considerations from evolutionary biology and empirical findings from behavioral research . It claims that “the receiver of a signal is interested in the reliability or accuracy of the signal and will ignore a signal if it is not reliable.” According to the theory, “credible” is a social signal especially when it is with it a handicap is connected, a difficulty: “Handicaps, also called 'expensive signals', are, for example, the peacock's wheel, the nightingale song or the lion's mane, all characteristics that do not reveal any biological usefulness at first glance, but still evolve Endure. ”Anyone who, despite their energy-sapping trait, competes with their own species or even outperforms their competitors despite the apparent waste of energy, send the signal to their environment, for example, that they are particularly vigorous and potent. According to the theory, a handicap can also demonstrate “strength”. This applies in particular to finding a partner and sexuality .

The handicap principle was formulated in 1975 by the Israeli biologist Amotz Zahavi and through the book The Handicap Principle published in 1997 together with his wife Avishag Zahavi . A Missing Piece of Darwin's Puzzle widely known. It claims to complement the mechanisms of sexual selection .

Basic assumptions of the theory

Amotz and Avishag Zahavi described the basic idea of ​​the handicap principle as “very simple: Waste can make sense because it shows conclusively that you have more than enough and have something to waste. It is precisely the effort - the waste itself - that makes the statement so reliable. ”The theory was backed up by various field studies and other empirical findings and has since been used in behavioral biology to explain conspicuous ornaments of a visual, acoustic or olfactory nature.

This interpretation of body and behavioral characteristics diametrically contradicts the “dead end theory”, according to which the male peacock , for example , fell into an evolutionary dead end because the females have preferred sexual partners with the largest and cleanest possible tail feathers since ancient times. He could no longer get out of this "dead end", although the tail plumage prevented him from flying and thus considerably restricted his ability to flee quickly. According to the handicap principle, it is precisely this obvious disadvantage that makes his suitability as a sexual partner credible for the courted female.

The handicap principle can therefore explain the emergence of characteristics that cannot be directly derived from considerations of suitability for natural selection or that seem to contradict the principle of increasing fitness .

Examples

Gazelle : The fur on the abdomen can serve as a social signal.
The lion's mane is an example of an "expensive" coat.
Pied flycatcher clutch: The bright blue eggs are visible from afar.
Male lions

Male African lions can develop impressive dark manes . In a long-term study in the Serengeti , a connection in particular between the color of this hair and the testosterone level was demonstrated, the level of which in turn depends on the nutritional status of the male lions: the more testosterone there is in the blood, the darker the color of the mane. However, this coloring is associated with a clear handicap, with a significantly increased heat stress , because the temperature in blazing sun is significantly higher on the skin of dark-colored lions than on the skin of blond individuals. It was also proven that lionesses tend to accept dark-haired lions as sexual partners and that the length of the mane is a social signal to male conspecifics and can be interpreted as an indication of the fighting strength among rivals. This physical fitness signal therefore reduces the likelihood of risky fights.

Gazelles

In the introduction to their jointly written book, which was published in German translation under the title Signals of Understanding , Amotz and Avishag Zahavi illustrate the handicap principle using the example of the behavior of a resting gazelle that has discovered a predator close by: the gazelle jumps up, barks and kicks the ground with his front hooves. “The beating of their hooves on the desert floor can be heard from afar; its crooked horns and the light and dark markings on its forehead make it easy to see that the gazelle is looking at its enemy. [...] The gazelle often jumps into the air with all four legs several times. When it then runs, it swings its black tail conspicuously back and forth in front of its white, black-rimmed body. ”A gazelle behaves quite differently when, for example, it is startled by a car and flees:“ It races away in silence and uses it the local conditions so as not to be seen. "

In the light of the handicap principle, the three "costly" behaviors of the gazelle - barking, knocking and jumping - can be interpreted as signals to the predator: On the one hand, the animal signals that it has noticed the predator. By "wasting" its time jumping in the air and exposing its conspicuous rear end instead of fleeing quickly, it assures its counterpart "that it is able to escape from it." The predator, in turn, recognizes from its behavior, "that he has no prospect of surprising his prey and that this gazelle is in excellent physical condition ”. If the predator refrains from attacking, a senseless hunt will be avoided: The gazelle does not have to flee with maximum effort, and the predator saves its energy for a less powerful gazelle.

  • The conspicuously glowing rear of a fleeing rabbit can also be interpreted as a social signal to a predator in this sense.
Pied flycatcher

In 2006 a study was published on the importance of bluish egg color in pied flycatchers . Bluish eggs are much more noticeable in a nest than gray ones and thus almost an attractant for egg-eaters. In addition, the production of the pigment biliverdin in particular means a particularly high physiological effort for the mothers, and this can only have developed in the course of the tribal history if it has been followed by a corresponding benefit. The findings of the study are: the bluer the egg, the greater the chances for the hatched young bird that it will survive the first two weeks of life in a healthy condition. However, this is not directly due to the blue color. Rather, the color is just a sign that the mother was healthy. In addition to the dyes, she was also able to pass on many maternal antibodies to the offspring. In this way, chicks made from strongly colored eggs could defend themselves better against pathogens than chicks made from weakly colored eggs. The researcher assumes that the color also serves as a signal to the parents: the bluer the eggs, the more worthwhile to incubate them. In a follow-up study in 2005 it was reported that males are more involved in brood care when the eggs are particularly intensely colored.

Further examples
  • Amotz and Avishag Zahavi also derive the development of particularly heavy horns, as in the case of the great kudu, from the working of the handicap principle. In the early stages of the evolution of horns and antlers, they suspect that small protuberances - comparable to the frontal cusps of giraffes - served as a supporting signal that indicated the direction of gaze. The somewhat longer but thin spear horns of the male Nilgau antelopes are also social signals: the males of this species fight their rivals by hitting them with their front legs. The hard, sharp horns of the females of several species of gazelle, however, are effective weapons against small predators. “Then signal selection came back into play and resulted in heavy and twisted or branched horns that signal the strength and endurance of those who wear them. The result was the heavy, backward-curved horns of the ibex , the spiral horns of the great kudu, the forks of the roebuck ", which however" usually do not prove to be particularly good as conventional weapons ".
  • Certain vocalizations by birds and other animals, which were often interpreted as warning calls for their fellow species (so-called hatred ), can also be interpreted as a signal to a potential predator, in the sense of: "I noticed you, I can afford it, to expose me so that you can find me, because I am skillful enough to flee from you in time. "
  • Other examples that Amotz and Avishag Zahavi explain in detail in their book Signals of Understanding include: a. the rutting cries of the deer , the striking plumage of some pheasants , the songs and long courtship flights of the larks , the "dancing" of the black grouse , the "bridal gifts" of the seagulls , the hours of crickets singing and the flares of the fireflies .

reception

“The handicap principle is one of the most influential concepts in evolutionary biology.” This statement, published in a specialist journal in 2015, is particularly noteworthy because critics put it before their study, in which the connection between the credibility of a characteristic and its “ Costs ”was questioned. This study is part of a scientific debate initiated by Amotz Zahavi in ​​1975, in the field of developmental psychology and immunology , in management processes , in considerations of aesthetics and even in warfare, and which has continued for decades.

At first, the concept met with massive criticism, in particular from John Maynard Smith , to whom the concept of the evolutionarily stable strategy can be traced back, but also from other authors who argued against the handicap principle, particularly with mathematical models. Amotz Zahavi himself and other authors, however, defended the concept. Other authors put the concept into perspective insofar as it was not the only plausible explanation for how credible signals could be sent, for example, reference was made to the concept of runaway selection .

In retrospect, it was explained in 2011 that mathematical modeling initially did not confirm the theory, but succeeded in 1990 after Alan Grafen had written two publications on population genetic models. Already in 1995, the theory was "widely accepted" ( Widely accepted ) described, however the scientific debate stops around the question of how an evolutionary balance between advantages and disadvantages can be explained, until recently at.

In the Encyclopedia of Evolutionary Psychological Science , however, the authors of the keyword Handicap Principle came to the following final assessment in 2018: “Scientists initially rejected the concept, but have now basically agreed with it. Although the concept seems blatantly counter-intuitive at first glance, the logic on which it is based is well-founded and shows the characteristics of a good scientific theory: verifiable hypotheses, unifying explanations for different phenomena, parsimony , broad scope as well as heuristic and prognostic ability. The concept is supported by mathematical and empirical findings and changed the way we look at communication between animals. "

Web links

Individual evidence

  1. ↑ a b Amotz Zahavi and Avishag Zahavi : Signals of Understanding. The handicap principle. Insel Verlag, Frankfurt am Main 1998, p. 383, ISBN 345816927-X .
  2. ↑ Eckart Voland : Sociobiology: The arena of the honest. On: faz.net from January 3, 2007.
  3. ↑ Amotz Zahavi: Mate selection - A selection for a handicap. In: Journal of Theoretical Biology. Volume 53, No. 1, 1975, pp. 205-214, doi: 10.1016 / 0022-5193 (75) 90111-3 .
  4. ^ Sara M. Clifton, Rosemary I. Braun and Daniel M. Abrams: Handicap principle implies emergence of dimorphic ornaments. In: Proceedings of the Royal Society B: Biological Sciences. Volume 283, No. 1843, 2016, 20161970, doi: 10.1098 / rspb.2016.1970 .
  5. ^ Peyton M. West and Craig Packer: Sexual Selection, Temperature, and the Lion's Mane. In: Science . Volume 297, No. 5585, 2002, pp. 1339-1343, doi: 10.1126 / science.1073257 .
  6. ↑ Amotz Zahavi and Avishag Zahavi: Signals of Understanding, pp. 13–15.
  7. ^ Judith Morales, Juan J. Sanz and Juan Moreno: Egg color reflects the amount of yolk maternal antibodies and fledging success in a songbird. In: Biology Letters. Volume 2, No. 3, 2006, doi: 10.1098 / rsbl.2006.0471 .
  8. ↑ Juan J. Soler, Juan Moreno, Jesús M. Avilés, and Anders P. Møller: Blue and green egg-color intensity is associated with parental effort and mating system in passerines: Support for the sexual selection hypothesis. In: evolution. Volume 59, No. 3, 2005, pp. 636-644, doi: 10.1554 / 04-159 .
  9. ↑ Amotz Zahavi and Avishag Zahavi: Signals of Understanding, pp. 164–166.
  10. ↑ Amotz Zahavi and Avishag Zahavi: Signals of Understanding, pp. 23–28.
  11. ↑ Simon M. Huttegger, Justin P. Bruner and Kevin JS Zollman: The Handicap Principle Is an Artifact. In: Philosophy of Science. Volume 82, No. 5, 2015, doi: 10.1086 / 683435 , full text (PDF) .
  12. ↑ Wolfgang Schneider and Friedrich Wilkening: Theories, models and methods of developmental psychology. Encyclopedia of Psychology, Volume 1. Hogrefe, Göttingen 2006, p. 517, ISBN 978-3-80170586-2 , full text of Chapter 10 (PDF) .
  13. ^ Ivar Folstad and Andrew John Karter: Parasites, Bright Males, and the Immunocompetence Handicap. In: The American Naturalist. Volume 139, No. 3, 1992, pp. 603-622, doi: 10.1086 / 285346 .
    ML Roberts, KL Buchanan and MR Evans: Testing the immunocompetence handicap hypothesis: a review of the evidence. In: Animal Behavior. Volume 68, No. 2, 2004, pp. 227-239, doi: 10.1016 / j.anbehav.2004.05.001 .
  14. ↑ Matthias Nöllke: Management bionics. How animals and plants can inspire leaders. Haufe, Freiburg - Munich - Stuttgart 2019, pp. 125–127, ISBN 978-3-648-12404-8 .
  15. ↑ Eckart Voland: The 'handicap principle' and the biological revolution of the aesthetic judgment.
  16. ↑ Zhanshan Ma, Frederick T. Sheldon and Axel Krings: The Handicap Principle, Strategic Information Warfare and The Paradox of Asymmetry. Oak Ridge National Laboratory, Oak Ridge (Tennessee, United States of America), April 2010, PDF .
  17. ↑ Amotz Zahavi and his Handicap Principle. Overview of various studies in which the handicap principle was tested.
  18. ↑ John Maynard Smith : Sexual selection and the handicap principle. In. Journal of Theoretical Biology. Volume 57, No. 1, 1976, pp. 239-242, doi: 10.1016 / S0022-5193 (76) 80016-1 .
  19. ↑ JWF Davis and P. O'Donald: sexual selection for a handicap: A critical analysis of Zahavi's model. In: Journal of Theoretical Biology. Volume 57, No. 2, 1976, pp. 345-354, doi: 10.1016 / 0022-5193 (76) 90006-0 .
  20. ↑ Mark Kirkpatrick: The Handicap Mechanism of Sexual Selection Does Not Work. In: The American Naturalist. Volume 127, No. 2, 1986, pp. 222-240, doi: 10.1086 / 284480 .
  21. ^ Ian PM Tomlinson: Diploid models of the handicap principle. In: Heredity. Volume 60, 1988, pp. 283-293, doi: 10.1038 / hdy.1988.44 .
  22. ↑ Amotz Zahavi: The cost of honesty: Further Remarks on the Handicap Principle. In: Journal of Theoretical Biology. Volume 67, No. 3, 1977, pp. 603-605, doi: 10.1016 / 0022-5193 (77) 90061-3 .
  23. ^ Graham Bell: The Handicap Principle in Sexual Selection. In: evolution. Volume 32, No. 4, 1978, pp. 872-885, doi: 10.2307 / 2407500 , full text (PDF) .
  24. ↑ Susan M. Leech and Marty L. Leonard, Begging and the risk of predation in nestling birds. In: Behavioral Ecology. Volume 8, No. 6, 1997, pp. 644-646, doi: 10.1093 / beheco / 8.6.644 .
  25. ↑ Gilbert Roberts: Competitive altruism: from reciprocity to the handicap principle. In: Proceedings of the Royal Society B. Volume 265, No. 1394, 1998, pp. 427-431, doi: 10.1098 / rspb.1998.0312 , full text (PDF) .
  26. ↑ Szabolcs Számadó: The cost of honesty and the fallacy of the handicap principle. In: Animal Behavior. Volume 81, No. 1, 2011, pp. 3–10, doi: 10.1016 / j.anbehav.2010.08.022 .
  27. ↑ Gerald Borgia: The Cost of Display in the Non-Resource-Based Mating System of the Satin Bowerbird. In: The American Naturalist. Volume 141, No. 5, 1993, pp. 729-743, doi: 10.1086 / 285502 .
  28. ↑ Andrew Pomiankowski: The 'handicap principle' works without Fisher. In: Trends in Ecology & Evolution. Vol. 2, No. 1, 1987, pp. 2-3, doi: 10.1016 / 0169-5347 (87) 90189-3 .
  29. ^ Andrew Pomiankowski: Sexual selection: the handicap principle does work - sometimes. In: Proceedings of the Royal Society B. Volume 231, No. 1262, 1987, doi: 10.1098 / rspb.1987.0038 .
  30. ↑ Jonathan Grose: Modeling and the fall and rise of the handicap principle. In: Biology & Philosophy. Volume 26, No. 5, 2011, pp. 677-696, doi: 0.1007 / s10539-011-9275-1 .
  31. ^ Alan Grafen : Sexual selection unhandicapped by the fisher process. In: Journal of Theoretical Biology. Vol. 144, No. 4, 1990, pp. 473-516, doi: 10.1016 / S0022-5193 (05) 80087-6 .
  32. ^ Alan Grafen: Biological signals as handicaps. In: Journal of Theoretical Biology. Vol. 144, No. 4, 1990, pp. 517-546, doi: 10.1016 / S0022-5193 (05) 80088-8 .
  33. ↑ Shigeo Yachi: How can honest signaling evolve? The role of handicap principle. In: Proceedings of the Royal Society B. Volume 262, No. 1365, 1995, doi: 10.1098 / rspb.1995.0207 .
  34. ↑ Patrick Kane and Kevin JS Zollman: An Evolutionary Comparison of the Handicap Principle and Hybrid Equilibrium Theories of Signaling. In: PLoS ONE. Volume 10, No. 9, 2015, e0137271, doi: 10.1371 / journal.pone.0137271 .
  35. ^ Dustin J. Penn and Szabolcs Számadó: The Handicap Principle: how an erroneous hypothesis became a scientific principle. In: Biological Reviews. Online publication from October 23, 2019, doi: 10.1111 / brv.12563 .
  36. ↑ Laith Al-Shawaf and David MG Lewis: The Handicap Principle. In: Todd K. Shackelford and Viviana A. Weekes-Shackelford (Eds.): Encyclopedia of Evolutionary Psychological Science. Springer, Cham 2018, full text .