PT - JOURNAL ARTICLE AU - Wible, Brad TI - Crossing borders along an endless frontier AID - 10.1126/science.356.6339.694-a DP - 2017 May 19 TA - Science PG - 694--694 VI - 356 IP - 6339 4099 - http://science.sciencemag.org/content/356/6339/694.1.short 4100 - http://science.sciencemag.org/content/356/6339/694.1.full SO - Science2017 May 19; 356