Product lines need to constantly evolve in response to market and technology changes. The diverging forces from marketing and engineering entail an intricate balance between satisfying changing customer needs and maintaining commonality in product platforms. This paper reports an evolutionary approach for product line design. Discrete choice analysis and product commonality indices are developed to evaluate the 'fitness' of a product line from marketing and engineering, respectively. Product line adaptation is formulated as a multi-objective optimization problem, whereby a solution framework based genetic algorithms is developed and implemented with a case study of notebook product line design.