A4.1.3 Evidence for evolution from selective breeding of domesticated animals and crop plants Notes

Selective Breeding is Strong Evidence for Evolution

1. Selective breeding mirrors the principles of natural selection, but with a key difference:
   1. Natural selection: Traits are selected by environmental pressures, favoring survival and reproduction.
   2. Artificial selection: Traits are selected by humans, based on preferences or utility.

Steps of Selective Breeding

1. A population contains heritable variation due to genetic differences (e.g., mutations, recombination).
2. Humans select parents that show traits considered valuable (e.g., high yield, docility, rapid growth).
3. These parents are bred together and produce offspring.
4. Offspring are screened for the desired traits, and only those with the strongest expression are selected for further breeding.
5. Over many generations, the trait becomes fixed in the population.

Examples of Selective Breeding

Domesticated Animals

1. Dogs (Canis lupus familiaris)

1. All modern dog breeds descended from gray wolves (Canis lupus).
2. Humans selectively bred wolves for traits like size, behavior, and coat type, leading to the wide variety of breeds we see today.

2. Chickens

1. Modern egg-laying hens produce hundreds of eggs annually, while their wild ancestor, the red junglefowl, lays only a few eggs per year.

Domesticated Crops

1. Maize (Corn)

1. Modern maize evolved from a wild grass called teosinte.
2. Early farmers selected plants with larger, softer kernels, transforming teosinte into the high-yield crop we rely on today.

2. Brassica Crops

1. The wild mustard plant (Brassica oleracea) is the ancestor of crops like cabbage, broccoli, kale, and cauliflower.
2. Selective breeding focused on different traits:
   1. Cabbage: Large, tightly packed leaves.
   2. Broccoli: Dense flower buds.
   3. Kale: Large, edible leaves.

How Selective Breeding Supports Evolution

1. Selective breeding shows that populations can undergo heritable changes in a relatively short period of time.
2. It proves that allele frequencies shift when certain traits are favored, just like in natural selection.
3. It demonstrates that small genetic differences accumulate, leading to major phenotypic divergence between breeds/varieties.
4. It mirrors the process of natural selection, except that the selective agent is human choice rather than the environment.

Implications for Evolutionary Theory

1. Selective breeding strengthens the evidence that:
   1. Heritable variation exists in populations.
   2. Traits can accumulate over generations.
   3. New varieties (and potentially new species) can emerge.
2. It provides a miniature model of evolution, showing that gradual accumulation of changes can have large evolutionary consequences.