Anyone who objects the size of the modern broiler and the speed at which today’s chickens grow may want to stop and pause a little as yearning for a return to the chickens of the past may not be that clear cut.

The size of chickens that we are now accustomed to bears little relation to that of chickens half a century ago, but go back to the late medieval period and even their birds would have been perhaps almost unrecognizable to farmers and consumers a few centuries before.

The findings have come from chicken bones collected by Museum of London Archaeology, uncovered at 74 sites in the city and analyzed by a group led by the University of Leicester.

Almost 500 tibiotarsus distal breadth measurements were compared with those from modern broilers and red jungle fowl. The bones dated from Roman times through to the late nineteenth century.

From Roman London through to 1340, the measurements showed little difference when compared with those of their red jungle fowl ancestors, but then things began to change.

Up to 1650, there was a sustained increase in the size of chickens, along with other domesticated livestock and, after that, the average measurements were fairly constant.

While these changes may not have occurred in the dramatic way that we have seen since the mid-twentieth century, the records reveal that human-directed selection was already leading to a different bird from its red jungle ancestor well over half a millennium ago.

But why did this happen, and might the changes that are visible from the fourteenth century actually have started even earlier?  Separate research may help to answer that.

Role of religion?

Separately, a team of international scientists led by the UK’s Oxford University has combined ancient DNA analyses with statistical modelling to pinpoint the timing of the selection for traits associated with modern chickens, and have found that medieval Christians who fasted may have played a part in producing less aggressiveness.

The team found that traits linked with reduced aggression and an ability to live in confined, smaller spaces and with other birds emerged about 1000 AD in the European Middle Ages.

These strong selection pressures coincided with an era in which Christians had widespread influence on what people should eat, introducing edicts that enforced fasting and the exclusion of four-legged animals from the menu.

The work suggests that religious edicts allowing people to eat chickens and eggs during fasts, couple with increasing urbanization, may have driven the evolution of modern domesticated chickens.

Bigger birds, access to less space, rising demand for meat due to the growth of towns and cities – little changes!