In the spirit of open mindedness and reason, let us hope that a better and more nuanced understanding of hybridisation and the species concept leads us to a better understanding of the nature of all life on earth
A hybrid between a donkey and a zebra. Photo: iStock This is the last of a four-part series.
In 2017, scientists sequenced the entire genomes of four bear species, making it now possible to analyse the evolutionary history of all bears at the genome level. The research shows that gene flow, or gene exchange, between species by extensive hybridisation, is possible between most bear species.
The detected gene flow among bears questions the very basic biological concept of a species. The biological species definition assumes that different species cannot produce offspring in the wild or that hybrid offspring are sterile.
The best-known example of this is the mule — a hybrid between a horse and a donkey, although examples do exist of fertile mules as well. However, it has been observed that grolars, the hybrids between polar and grizzly bears, are often fertile.
Axel Janke of the Senckenberg Biodiversity and Climate Research Center in Frankfurt, one of the scientists involved in the bear evolutionary study has stated, “We have to ask ourselves: Does the species concept still hold true, given there is evidence of gene flow not only in bears, but also in other animals? Therefore, what do we need to protect for the future — species or genomic diversity?”.
Remarkable studies on hybridisation and the species concept have also emerged from Werner Kunz in his book, Do Species Exist? and Eugene McCarthy in his comprehensive book, Handbook of Avian Hybrids of the World.
These books point to the need to reexamine and rethink the entire species concept. The late conservationist Billy Arjan Singh, who established Dudhwa National Park in Uttar Pradesh, very often emphasised that hybridisation could invigorate the gene pool of animals like the tiger and he stated this in reference to his tigress Tara, whose genetic makeup was considered to be controversial because she might have been a hybrid between a Siberian and a Bengal tiger, a cross of two subspecies.
Modern-day science, recognising the fluidity of the concepts of species and subspecies, is giving us strong indicators that Billy Arjan Singh might have been right, after all, in his views on gene exchange and hybridisation.
In a paper entitled, Planning tiger recovery: Understanding intraspecific variation for effective conservation, the authors state: “Basing current conservation strategies on numerous subspecies, for which there is little or no scientific support, may actually hinder the tiger’s survival by preventing large-scale cooperative conservation management programs, such as conservation captive breeding, reintroduction initiatives, or trans-boundary projects, which will be restricted to the currently recognized putative subspecies.”
Gayal, a hybrid between a Gaur and domestic cattle in Alipore Zoo in Calcutta, 1992. Photograph by Shubhobroto Ghosh
Despite the monumental scientific importance attached to hybrid big cats and other animals in understanding evolutionary processes and genetics, it has to be stated that most captive animal operators breed hybrid big cats and other animals for making money rather than for any genuine scientific objective in mind.
Therefore there is a need to bring in appropriate legislation wherever necessary to control / curb the breeding of hybrid big cats as indeed of any big cats or any animals in captivity.
In many ways, the species concept in biology resembles the concept of constellation in astronomy, that is, it is a concept that exists in the human imagination for convenience but not in reality.
The doyen of evolutionary biology, Charles Darwin, was puzzled by hybridisation and the species concept throughout his life and in a letter to the botanist Joseph Hooker in 1856, stated:
“I have just been comparing the definitions of species [...] It is really laughable to see what different ideas are prominent in various naturalists' minds, when they speak of ‘species’; in some, resemblance is everything and descent of little weight — in some, resemblance seems to go for nothing, and Creation the reigning idea — in some, descent is the key — in some, sterility an unfailing test, with others it is not worth a farthing. It all comes, I believe, from trying to define the undefinable.”
In the spirit of open mindedness and reason, let us hope that a better and more nuanced understanding of hybridisation and the species concept leads us to a better understanding of the nature of all life on earth.
Acknowledgements : Rahul Majumdar, Dr Anindya Sinha, senior scientist, National Institute of Advanced Studies, Bangalore, Piyali Chattopadhyay Sinha, Ashish Samanta and Shibaji Bhattacharya, Alipore Zoological Gardens, Kolkata, Payel Biswas of Institute of Urban Transport, New Delhi, Subhodip Bid of National Library, Kolkata and Anirban Chaudhuri all contributed in locating the historical records of hybrid big cats in Alipore Zoo in Kolkata. The authors extend their gratitude to Dr M K Ranjitsinh and Ms Ekta Sodha, CEO of Cadmus Sodha Schools in Jamnagar for their help in confirming the record of Ranji, the tiger X lion hybrid in the zoo of His Highness, the Jamsahib Ranjitsinhji, Maharajah of Nawanagar, Gujarat, India.
Shubhobroto Ghosh is author of the Indian Zoo Inquiry and the book, ‘Dreaming In Calcutta And Channel Islands.’ He is now Project Manager of Wildlife at World Animal Protection in India.
Karin Saks is a primatologist based in South Africa. Since 1997, Karin has been involved in the fostering and rehabilitation of orphan baboons, the caring of injured monkeys who have been returned to the wild and has worked towards a harmonious co-existence between these primates and humans. She has many publications on primates and has been the subject of television programmes and films.
Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth
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