Chickens are the actual and symbolic product of humanity’s influence on the planet, scientists have established.
The sheer numbers of the bird (Gallus gallus domesticus) as well as changes to its height and mass brought on by specialised breeding programs initiated in the 1950s “vividly symbolise the transformation of the biosphere to fit evolving human consumption patterns”.
That’s the conclusion reached by researchers headed by Carys Bennett from the UK’s University of Leicester and published in the journal Royal Society Open Science.
The scientists suggest that the modern domesticated chicken serves as solid evidence for the classification of the current period in world history as the “Anthropocene”.
First popularised in 2000 by Nobel laureate Paul Crutzen, the term denotes a time in which the Earth is totally dominated and largely reconfigured by humans. Among scientists, the term is a controversial one, with many feeling it has more to do with pop-culture than empirical evidence.
Even among those who feel it has some merit, debate rages over when the period took over from the Holocene, which is universally agreed to have kicked off 11,700 years ago at the conclusion of the most recent ice age.
Estimates for the start of the Anthropocene range from 900CE to 1950.
Bennett and her colleagues tend to favour the more recent end of the spectrum, and indeed cite as a key marker the post-war advent of a competition launched by the US Atlantic and Pacific supermarket chain to encourage farmers to breed a fatter bird. The competition was called Chicken of Tomorrow.
The results of the quest – and other similar efforts particularly in industrialised nations faced with growing populations and (for a while at least) improving household incomes – were spectacular.
Today, the scientists report, chickens are by far the most numerous bird on the planet, with a standing population of 21.4 billion. This compares to house sparrows at half a billion, and ducks at 1.1 billion.
“In Europe,” write the researchers, “the population of domesticated chickens in 2009 (1.9 billion) was greater than the combined population of the 144 most numerous wild bird species (1.6 billion). It is likely to be the largest standing population of a single bird species in history.”
But it’s not just numbers in play when it comes to chicken dominance; it’s heft as well.
Since the Chicken of Tomorrow program, the researchers write, “chickens have undergone extraordinary changes. From the mid-twentieth century to the present, broiler growth rates have soared, with up to a fivefold increase in individual biomass.”
The modern chicken is, in fact, a wholly anthropogenic species, with its survival utterly dependent on the technology of intensive meat production. In the US 97% of broiler hens are reared in factory farms, and worldwide the figure drops only to 72%.
The chickens in turn are the bedrock of a massive worldwide industrial chain, running from battery facilities to KFC outlets that account for billions of dollars in trade, millions of jobs and which forms a central element of the lifestyle choices of much of the world.
The numbers are mindboggling. Bennett and colleagues report that just one US chicken producer, Tyson Foods, slaughters 35 million birds every week.
The company kills them when they are five weeks old. The modern species is so much a product of technology and factory-breeding that allowing the birds to live longer could conceivably be described as an act of cruelty.
“If left to live to maturity, broilers are unlikely to survive,” the scientists note.
“In one study, increasing their slaughter age from five weeks to nine weeks resulted in a sevenfold increase in mortality rate: the rapid growth of leg and breast muscle tissue leads to a relative decrease in the size of other organs such as the heart and lungs, which restricts their function and thus longevity.”
From that perspective, then, it is reasonable to designate the modern chicken as a species that typifies the overwhelming influence of humanity on the modern world.
Bennett and colleagues, however, also cite another. Chicken bones, in the past, have not played a huge role in the fossil record, because they are light and hollow and tend to either rot or be eaten. Today’s chickens, however, constitute a different set of potentials – not least because from time to time disease outbreaks necessitate the on-farm slaughter and mass burial of millions of birds.
Entombed thus, in oxygen-free conditions, the bones are likely to remain, perhaps for millions of years.
“The broiler chicken is therefore likely to leave a widespread and distinctive biostratigraphic signal in the sedimentary record, as a key fossil index taxon of the Anthropocene,” the researchers conclude.
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