Humans have been breeding animals and plants with the most desirable characteristics for thousands of years. For example, the fattest pigs and the cows with the highest yield of milk were chosen for breeding. Fruits and vegetables are carefully selected and those that have grown fuller than others are used as the prime source of seeds for the following harvest.
However, breeding and cross breeding entered a more complexdimension in the 1970s with the discovery of genetic engineering and more recently synthetic biology. The manipulation or creation of biological components to form systems that are not found in the natural world has given us yet more power to direct evolution.