For millennia, plants have been selectively bred to develop varieties that are are productive, or more suitable for human use. Recent decades have seen much progress in the use of plant biotechnology in food production, particularly in terms of gene transfer technology. This progress has been accompanied by changing public attitudes to plant biotechnology and increased ethical awareness, with concerns relating to the plant or gene itself or to health and environmental consequences. Some of the issues involved have been examined by a sub-committee of UNESCO's International Bioethics Committee.