This paper investigates the coding of causal-noncausal alternation in three West-African families of languages, studying divergence and convergence within and between these families. Atlantic, Mande and Mel languages belong to the same Niger-Congo phylum but display quite different typological profiles and have long lasting historical contacts in Senegal and the surrounding areas. In order to evaluate the correlation between typological profile and valence orientation and to identify contact-induced changes, the same eighteen verb-pair meanings have been analysed for all the documented Atlantic languages, and for the Mande and Mel languages in contact with them. A new methodology was designed for this, combining family standard-patterns and measure of deviation of individual languages. After overcoming biases in the list of pairs due to verb types and animacy, the results confirm the expected correlation between the favored coding strategies and the typological profiles. Moreover, beside pointing to some contact-induced changes and revealing a strong internal variation inside Atlantic family, attributed here to its historical depth, this study shows that some structural features may favor or preclude specific coding strategies. In this view, the equipollent strategy appears to be important for some languages and usefully included into a new typological cluster of derivational strategies.