Botany: An Introduction to Plant Biology - Mauseth, James D. 2017

Genetics and Evolution

Part Opener Image: Legumes are rich in protein and have been an essential part of the diet of human beings for thousands of years. During that time people noticed differences in the seeds they harvested; some tasted better, some had attractive colors, some seemed to satisfy hunger longer. In addition, they searched for plants that seemed similar to the legumes they knew, hoping to find new types of beans, peas, and lentils. These early people cultivated the seeds they liked the best and discarded others. Gradually, a wide variety of legumes entered our diet. Selection like this, performed by people, is artificial selection, whereas selection that occurs in nature is natural selection. Both result in evolutionary change.

The focus of this part is the mechanism by which DNA and its information are passed from parent to progeny; how that DNA changes over time, resulting in new types of organisms; and how the environment and natural selection have interacted to produce hundreds of thousands of species of prokaryotes, algae, fungi, animals, and plants.

DNA serves as an archive of information that, interacting with environmental information and resources, produces an organism’s body—its structure, metabolism, and biology. DNA also carries the information needed to make more DNA so that during reproduction—either of the cell or of the entire organism—each progeny receives copies of the DNA and the information it contains. Errors occur occasionally, and molecules of DNA are not copied perfectly; each version may code for slightly different enzymes or in some other way produce an organism slightly different from parents or siblings. If the world were absolutely uniform, we might expect that whenever a mutation resulted in a new type of individual, either the new type or the original would be favored by natural selection until it was the only type left; a more advantageous metabolism or structure would be more advantageous everywhere.

However, our world is complex, containing aquatic and terrestrial environments, areas with mild temperatures and others with temperature extremes, and a diversity of rainfall, soil types, pathogens, pollinators, and so on. Consequently, alternative biologies may each be selectively more advantageous in different conditions. The diversity and richness of the environment result in diversity and richness of organisms.