Many plant species recognize kin and respond with changes in functional traits. Researchers hypothesize that siblings compete less than strangers. However, no study has directly tested whether siblings are less competitive. Measuring natural selection on kin recognition responses in root allocation and other destructively measured traits is challenging, since trait and fitness cannot be measured on the same individual. Here, a methodology using family-level selection is developed, measuring the trait on one individual and measuring its fitness value using another related individual. Three greenhouse pot experiments were conducted using six Brassica oleracea cultivars at two nutrient levels. We investigated whether root allocation and morphological traits were under natural selection. We tested whether or not there was cultivar recognition or resource partitioning in B. oleracea. We found that putative competitive traits (size, height, emergence and root allocation) had expected patterns of individual selection for an increase in each trait and group selection for a reduction of each trait. There was no indication that resource partitioning was occurring or that B. oleracea could recognize cultivars. However, plants were experiencing competitive interactions within pots. In conclusion, we demonstrate that using family-level selection estimates the fitness consequences of root allocation and morphological traits. / Thesis / Master of Science (MSc)