The role of behaviour in evolution

Species behaviour has the potential to lead morphological evolution, by placing the organism under novel selection pressures.

Many adaptations of living species could have originated in this way, although there are few documented examples.

Our research focuses on the fossil record, a potentially rich but under-exploited source of information on the role of behaviour in evolution.

The behaviour of fossilised species is traditionally deduced from their morphology. This prevents researchers from observing behavioural changes that may occur prior to morphological evolution. Examining behavioural indicators independent of adaptive morphology may help us to address this problem.

Preserving behaviour

Examples of 'fossilised behaviour' include dietary information (wear traces on teeth and stable isotopes) and trace fossils indicating locomotor mode (footprints). The signature of a behavioural lead would be an observed shift in behaviour from one horizon (or species) to another, followed later by a morphological change relating to function.

Fossil case studies that suggest a behavioural role in evolution include:

• feeding shifts in finely resolved sequences of vertebrates, ranging from freshwater fish to terrestrial ungulates
• locomotion changes crucial to major evolutionary transitions in the origin of tetrapods, birds and humans 

These examples suggest that behaviour is central to the process known as exaptation, in which structures acquire new functions.

In our research we are looking at the factors leading to changes in the form of mammalian teeth as they switch to new diets, usually in response to a change in the availability of different plants in response to natural climate change in the past. 

We are studying the evolution of elephants and their relatives in Africa and in Europe over the past 20 million years. The transition from eating mainly soft leaves of trees to coarser leaves of grasses was crucial to the evolution of true elephants starting some 8 million years ago. Elephants acquired high-crowned teeth with multiple enamel ridges to resist increased tooth wear.

We are collecting data on tooth morphology, climate change and vegetation change to determine if the change started as a behavioural one, and whether it was driven mainly by the coarser vegetation itself, or by the ingestion of abrasive dust with the animals’ food.

We have also studied how diet has varied even within individual species of herbivorous mammals, and how this is determined by the particular habitat inhabited. Here we have looked at a range of mammals (deer, horses, bovids, elephants etc) through the Ice Ages in Europe (roughly the last 2 million years).

Some species are much more flexible than others, and this may have aided survival through changing climatic conditions. An interesting question is whether this behavioural flexibility encourages or inhibits new morphological adaptations to diverse foods.