Scientists have tried to explain for quite some time now why male ungulates possess such large antlers and horns.

When Charles Darwin emitted his famous theory of evolution and natural selection, he pointed out that the size of male ungulate antlers and horns signals a male's individual fitness, and thereby are used by conspecifics as an honest mark of male sexual vigor, health, strength, hierarchical status, or fighting ability.

The sexual selection theory says that an organism that affords to develop larger antlers or horns carries a higher capacity to get advantage of the resources.

A mixed team from five institutes in three European countries (CEFS-INRA, LBBE- CNRS , and ONCFS in France; Grimsö Wildlife Research Station in Sweden; and CEES in Norway) have focused for the first time on this issue in a territorial ungulate species, the European roe deer.

The team led by Cécile Vanpé investigated long-term data on antler size from three contrasting populations of roe deer (Bogesund in Sweden, and Chizé and Trois Fontaines in France). They discovered that antler size was a real signal of the male's individual fitness linked to age and body mass. "Our results provide evidence that antler size of male roe deer mainly reflects their age and body mass, and is more resilient to variation in environmental conditions such as climate, food resources, and density", said Jean-Michel Gaillard.

"Body mass and age are both reliable descriptors of individual quality in most vertebrates and have been shown to affect the ability to fight and the dominance of males. Hence, by choosing their sexual partners on the basis of their large antlers, females may thus ensure that they mate with a high quality mate," said Cécile Vanpé.

"Males may also use antler size of rival males as a cue to assess the possibility of winning a fight in order to control and monopolize more females for reproduction", explained Mark Hewison. "This leads to the key question of whether males with larger antlers do have greater access to females than other males", added Petter Kjellander.

The team signals that antler size should be considered in management rules as an indicator of individual quality.