Speech does not fossilize but the interpretation of artefacts obtained from archaeological sites can be used to infer the degree of complexity of the communication system necessary to produce these artefacts and sometimes their associated behaviour. The degree of complexity of tool technology is often used as a marker for the level of cognitive ability but it is difficult to extrapolate the need of a sophisticated system of communication from tool technology alone. One reason is that the ability to manufacture complex tools can be learned from observation and imitation without explicit tutoring requiring the use of language. Intentional burials and sea faring are activities that appear to require a greater reliance on linguistic communication for the purpose of enacting rituals and solving problems.