ACADEMIA Letters Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Joseph Jordania, University of Melbourne Few propositions are believed in biology as strongly as Charles Darwin’s theory of evolutionary reasons behind the amazing beauty of the peacock’s tail (the professional term for this impressive creation of nature is “train,” and the official name for the species is peafowl, Pavo cristatus). The peacock’s visual features were always considered so cumbersome and harmful for survival that it was believed that the only reason for the peacock’s sporting the huge tail was to entice female peahens with their beauty. According to this model, championed by Darwin and followed by generations of scholars, for a big and colourful peacock, it is more difficult to stay unnoticed, and therefore to survive predators, but this negative factor is overcompensated by another, positive factor: a more impressive tail enhances its bearer’s chances of having more mating opportunities and many offspring. Amotz Zahavi furthered Darwin’s initial idea by proposing the “handicap principle,” in which he argued that for the display of fitness to be honest, it should be a serious handicap to its bearer (Zahavi et al, 1997). Scholars were so sure about the sexual selection reason behind the attractiveness of a peacock’s dazzling display that they did not even consider it necessary to test this idea and to support it with an experiment or a field study until quite recently. Only at the beginning of the 1990s, more than a century after the publication of Darwin’s work on sexual selection (1871), did Marion Petrie, Tim Halliday, and Carolyn Sanders finally publish the results of their study on peacocks’ mating behaviour. According to their results, as expected, females chose males with bigger trains and with the largest number of eyespots (Petrie et al., 1991). Thus, the study confirmed what was already believed. Unfortunately, the study was very limited, as researchers studied only one lek (a congregation of males) of 10 males for a very limited time (one mating season, or more precisely, a bit over a Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 1 month), and the method employed did not convince everyone – researchers disfigured some of the males’ tail feathers and covered several eyespots to observe the results. A bigger study was needed. A few years later a much larger study was conducted. It was expected to confirm the Petrie et al. 1991 findings with solid field results. During seven long mating seasons (from 1995 to 2001), researchers from the Graduate School of Arts and Sciences at the University of Tokyo, under the leadership of Mariko Takahashi, studied the free-ranging population of Indian peafowl at Izu Cactus Park in Shizuoka, Japan (Takahashi et al., 2008). Very unexpectedly for them, the researchers came to the conclusion that the peahens were totally indifferent to the peacocks’ tail beauty and eyespot numbers, and that generally the tail condition did not correlate with the reproductive success of their bearers. It is difficult to know the reasons for the huge delay between the end of study and the appearance of the publication (possibly they were analysing field results? Or they had doubts whether it was worth publishing negative results?). Whatever the reasons, the publication of the results took another seven years (Takahashi et al., 2008). Discovery News presented the results as sensational: “The feather train on male peacocks is among the most striking and beautiful physical attributes in nature, but it fails to excite, much less interest, females, according to new research. The determination throws a wrench in the long-held belief that male peacock feathers evolved in response to female mate choice. It could also indicate that certain other elaborate features in galliformes, a group that includes turkeys, chickens, grouse, quails, and pheasants, as well as peacocks, are not necessarily linked to fitness and mating success” (Viegas, 2008). As we can see, instead of confirming the results of Petrie and her colleagues, the Japanese study actually provided falsification of the initial hypothesis. As expected, proponents of the sexual selection theory did not take the unwelcome news without a fight. Petrie and her French colleagues immediately wrote a rebuttal of the Japanese study (Loyau et al., 2008). Without rejecting the diligent Japanese study, they proposed that a phenomenon of “plasticity of female choice” might be involved. In plain English this term means that peahens might change their taste in choosing males very much as humans do, and that contemporary peahens are possibly not as interested in the size and beauty of the peacock tail as their grandmothers were. Theoretically possible, this explanation does not seem very convincing, as it seems hard to believe that, after hundreds of thousands (possibly even millions) of years of female excitement for their male counterparts’ trains, suddenly, during the 1990s (between the studies of Marion Petrie and Mariko Takahashi) peahens for some unknown reason lost interest in the peacock’s dazzling display. Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 2 Still in the 1990s, a modified sexual selection model was suggested by Merle Jacobs, author of the “food-courtship theory” (1999). The theory suggests that peahens are attracted to peacocks for the resemblance of their eyespots to blueberries. Creationists also benefited from this unexpected result and confusion among biologists after Takahashi’s results were published. If sexual selection was not behind the peacock’s tail, they mused, then what else could be the reason for this “unnecessary beauty” if not the will and aesthetic sense of the Creator?…So, let me ask the central question for this article: can there be an alternative explanation to sexual selection for the evolutionary reason behind the peacock’s dazzling train? We are often so blinded by the visual factor that we fail to notice other elements of morphology and behaviour. Have you ever seen a discussion of peacock’s voice or behaviour, together with their visual appearance? Most likely never! And as soon as we pay attention to these details, it becomes clear that the peacock’s dazzling tail might be just one, the visual element, of the so-called “aposematic display.” But what does this unusual term mean? “Aposematism” is one of the two very important opposing strategies of survival, another much better-known strategy being “crypsis.” The differences between them are easy to understand: Cryptic species (both predator and particularly prey species) try to survive predators by staying unnoticed. They are usually camouflaged, are mostly silent, try not to have a body odour, and as soon as they are noticed by a predator, they try to escape as fast as possible. Cryptic species are very good runners. Cats of various sizes and rabbits are examples of classic cryptic species among predator and prey species. Aposematic species (both predator and particularly prey species) do not try to conceal themselves. On the contrary, they try to “announce” their presence by all the possible modalities: they are often very visible by their contrastive body colours; they often make constant sounds as they walk; and they as a rule have a constant body odour and can produce stronger smell if threatened. Finally, when confronted by a potential predator, instead of running away, they try to intimidate the predator by their suddenly increased body size, threatening sounds, gestures, and fearless behaviour. Aposematic species are, as a rule, bad at running. Skunks and porcupine are examples of classic aposematic species. Aposematic species are more usual among prey species, as the predators that announce their presence are understandably less successful. Aposematism, for many biologists, is merely a “warning coloration,” but it is much more than coloration. For a species that uses aposematism as a survival strategy, it pays to use aposematic signals in every possible modality – not only visual signals. That is the reason that a skunk, when facing a predator, starts an elaborate display of various intimidating behaviours: it raises tail and even stands upright on its front legs, trying to look as tall as possible (visual signal), makes threatening growling sounds (audio signal), intensifies the body odour (still before using his deadly olfactory defence as the ultimate weapon), and to prove it is not Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 3 scared, keeps its ground without moving away from a predator. Now let us look at peacocks. Do they display any of these aposematic signals? Yes, it seems to me they do, and they display most of these signals. Apart from their already renowned huge and colourful tail, they have many other elements of classic aposematic species as well: the peacock has a very strong, piercing voice (audio signal), secretes very smelly droppings if handled against its will (olfactory signal), and often does not go away even if a potential danger, for example, a tiger or a leopard, is nearby. What about peahens – do they use any elements of aposematic display, or do only males behave aposematically? Yes, it is quite well known that peahens actively use their much smaller feathers when they need to defend their chicks from intruders and predators. We probably also need to discuss specifically whether peacocks’ strategy to avoid attacks from tigers (Panthera tigris) and leopards (Panthera pardus) is a viable one, as these predators might gradually learn to disregard peacock’s size and fearless behaviour and start attacking them. This element of peacocks’ behaviour can be only studied in the natural habitat of the peafowl, not in the feral populations living in the UK (where Petrie’s study was conducted) or in Japan (where Takahashi’s study was conducted). Unfortunately, no study of peafowl was ever conducted in India, where they naturally live. But fortunately for us, there is plenty of evidence that peacocks are not generally scared of big cats. George Schaller was probably the first scholar who noted that peacocks are not alarmed by tigers’ close proximity (1984:279). Also, the interested reader can easily see plenty of photos on the internet, taken in the wild, where peacocks are photographed in close proximity to tigers and leopards. Of course, it is also true that in some cases peacocks can be attacked and killed by these predators, but we need to remember that there is no aposematic animal that is guaranteed survival from predator attacks, including the legendary skunk, who is still sometimes killed by predators. As Ruxton wrote, the only guaranteed defence from predators is to kill the predator (Ruxton et al. 2004). I tried also to attach a few photos to this article to demonstrate peacock’s general disdain for the proximity of tigers and leopards (I am grateful to Samuel Singh, a member of Jim Corbett International Research Group member, who took most of these photos and provided them for my research. Photos were taken in Pilibhit tiger reserve in May 2019). Therefore, my suggestion is that the peacock’s amazingly big and beautiful train evolved primarily (or at least partly) under the forces of natural selection, and its evolutionary function was, and still is, to scare away predators (and rival males). By the way, the function of the peacock’s train to scare away the rival males has been long known to the proponents of sexual selection as well, and was discussed in Petrie et al. 1991 publication. Even earlier, in the 1930s, R. W. G. Hingston (1933) and J. Huxley (1938) pointed out that male adornment is instrumental in establishing dominance relationships among males. The ideas of sexual Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 4 selection via female choice, and aposematism display to scare predators are not mutually exclusive, on the contrary, the same feature that might attract females (like a big muscle body, or a colorful tail of enormous size) can be both attractive to females, and intimidating both for rivals and predators. How do things stand at the moment? The ground-breaking Japanese study of Takahashi sometimes gets simply neglected, and, for many, the sexual selection model is still the only explanation for the peacock’s dazzling tail (see, for example, a 2012 article by Patricia Brennan from the Department of Ecology and Evolutionary Biology, Yale University: no mention of the conflicting study results at all). It is difficult to understand why, after the publication of two similar experimental studies with very different results (Petrie at al., 1991 and Takahashi et al., 2008) no other studies were conducted during the last 13 years, although such clearly conflicting results should have naturally prompted the appearance of more studies. And closer to the end, I have to mention as well that the theory of sexual selection always had critics, including even Alfred Wallace, the co-discoverer of the theory of natural selection, and discoverer of the idea of “warning flags” that gave rise to the idea of aposematism. Unfortunately, Wallace himself never proposed the idea of “warning flags” to account for the peacock’s train size and beauty, although he was critical of the idea of that sexual selection accounted for the peacock’s amazing display. If we consider that to look bigger (and more colourful) is one of natural selection’s favourite strategies to scare away predators and competitors and avoid unnecessary physical confrontations, the idea that the peacock’s train was primarily aposematic seems very plausible. By the way, such strategies thrive not only among aposematic species, who use warning signals constantly, virtually every moment of their lives, and in every modality but also occur among most non-aposematic species (including the perfect predators – cats of all sizes), who use aposematic (or, more precisely, startling) “go away” signals occasionally to avoid unnecessary and potentially dangerous physical confrontations, and substitute ritualized non-violent aposematic displays for costly fights (see for example, Eibl-Eibesfeldt, 1979). Therefore, I propose to check the possibility that peacocks’ morphology and behaviour evolved primarily as an aposematic strategy of defence from predators and intimidation rivals. In 2016 (in the UK) and 2017 (in Portugal) I gave related presentations at two international meetings of behavioural ecologists, and I can say that, apart from rare exceptions, the reaction was that of suspicious distrust. Of course, we should not forget that the idea of sexual selection being behind the peacock’s dazzling train is one of the most trusted, and even the most loved theories in biology, and it will take time and more evidence to put even a slight doubt in the minds of proponents of sexual selection theory. So, I do not hope to prove wrong the theory of sexual selection behind the Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 5 peacock’s train with this small article. My aim is only to propose to the behavioural ecologists that in a wider discussion of the possible evolutionary reasons behind the beauty of peacock’s train, a discussion that seems long overdue, the forces of natural selection in general, and aposematic strategies in particular, be considered as well. References Brennan, Patricia L. R. (2012). Sexual Selection. Nature Education Knowledge 3 (10):79. Darwin, Charles. (1871. Second revised edition 1875). The Descent of Man and Selection in Relation to Sex. London, Murray. Eibl-Eibesfeldt, Irenaus. (1979). Ritual and ritualization from a biological perspective. In: Human Ethology: Claims and Limits of a New Discipline. Von Cranach et al. (ed.), Cambridge: Cambridge Univ. Press. pp. 3-55. Jacobs, Merle. (1999). A New Look at Darwinian Sexual Selection. Natural Science (10 March, 1999). Loyau, Adeline, Marion Petrie, Michel Saint-Jalme, M., and Gabriele Sorci. (2008). Do peahens not prefer peacocks with more elaborate trains? Animal Behaviour 76, e5-e9. Petrie, Marion, Tim Halliday, Carolyn Sanders. (1991). Peahens prefer peacocks with elaborate trains. Animal Behavior 41: 323-331. Ruxton, Graeme D., Thomas N. Sherratt, and Michael P. Speed. (2004). Avoiding attack. The evolutionary ecology of crypsis, warning signals, and mimicry. Oxford University Press. Schaller, George B. (1984). The Deer and the Tiger. Chicago: University of Chicago Press. Takahashi, Mariko, Hiroyuki Arita, Mariko Hiraiwa-Hasegawa and Toshikazu Hasegawa. (2008).Peahens do not prefer peacocks with more elaborate trainsAnimal Behaviour, 75(4), April: 1209-1219. Viegas, Jennifer. (2008). Female peacocks not impressed by male feather. Discovvery News, March 26, 2008. <http://dsc.discovery.com/news/2008/03/26/peacock-feathers-females. html> (visited on July 10th, 21). Zahavi, Amotz, Avishag Zahavi, Na’ama Ely, Melvin Patrick Ely. (1997). The Handicap Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 6 Principle: A Missing Piece of Darwin’s Puzzle. Oxford University Press. Appendix Peacocks in close proximity of their natural predators in India. Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 7 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 8 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 9 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 10 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 11 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 12 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 13 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 14 Academia Letters, September 2021 ©2021 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Joseph Jordania, josephjordania@yahoo.com.au Citation: Jordania, J. (2021). Can there be an Alternative Evolutionary Reason Behind the Peacock’s Impressive Train? Academia Letters, Article 3534. https://doi.org/10.20935/AL3534. 15