
Plant Breeding is a very measurable science -- its impact can be readily documented.
Some examples of yield gains:
| CROP | 1930 | 1975 | UNIT | % |
| Wheat | 14.2 | 30.6 | bu | 115 |
| Rice | 21.0 | 45.6 | cwt | 117 |
| Corn | 20.4 | 86.2 | bu | 320 |
| Oats | 32.2 | 48.1 | bu | 50 |
| Barley | 24.0 | 44.0 | bu | 85 |
| Sorghum | 10.8 | 44.0 | bu | 358 |
| Cotton | 157.0 | 453.0 | lbs | 188 |
| Sugar beets | 11.9 | 19.3 | tons | 62 |
| Peanuts | 659.4 | 2565.0 | lbs | 295 |
| Soybeans | 13.4 | 28.4 | bu | 112 |
| Potatoes | 65.9 | 251.0 | cwt | 311 |
| Tomatoes | 61.0 | 166.0 | cwt | 172 |
| Alfalfa | 1.95 | 2.87 | tons | 42 |
Remember that these figures are based upon genetic and cultural practices/improvements.
How can the changes due to genetics be partitioned from the changes due to improved cultural practices (environmental changes)?
Both cases have some undesirable confounding.