Carl Sagan explains Artificial Selection in Cosmos

Introduction

This tutorial explains the concept of artificial selection as illustrated by Carl Sagan in the "Cosmos" series, using the story of the Heike crabs as a case study. Understanding artificial selection helps us grasp how humans have influenced the evolution of species through selective breeding and environmental interactions.

Step 1: Understand the Historical Context

• Familiarize yourself with the story of the Heike clan in 12th-century Japan.
• Key events to note:
  • The Heike were ruled by a young emperor, Antoku.
  • They engaged in a fierce battle against the Genji clan at Dan-no-Ura in 1185.
  • The Heike faced defeat, leading to the drowning of many warriors and the young emperor.

Step 2: Recognize the Legend of the Heike Crabs

• Learn about the Heike crabs, which are said to have markings resembling a samurai's face.
• Understand the cultural significance:
  • Fishermen do not eat these crabs; instead, they throw them back into the sea as a tribute to the fallen warriors.
  • This practice unintentionally contributes to the crabs' survival and the propagation of their unique markings.

Step 3: Explore the Mechanism of Artificial Selection

• Define artificial selection:

  • It is the process where humans influence the survival and reproduction of species based on desired traits.

• Analyze how human actions lead to selection:

  • Fishermen throwing back crabs with human-like faces inadvertently favored those crabs for survival.
  • Over generations, this created a lineage of crabs with more pronounced facial markings.

Step 4: Identify the Implications of Artificial Selection

• Consider how this concept applies beyond crabs:
  • Many domesticated animals and cultivated plants have been shaped by human preferences.
  • Recognize that most species we encounter today have been selectively bred for specific traits.

Conclusion

Artificial selection is a powerful force that shapes the traits of the organisms around us, often without conscious intention. By understanding the story of the Heike crabs and how they came to bear the likeness of samurai warriors, we gain insight into the broader implications of our interactions with nature. Reflect on how this concept applies to modern agriculture and animal husbandry, and consider the ethical aspects of selection in contemporary practices.