Lecture on Species and Speciation

Introduction

Humans share more in common with each other than with other species like dogs.
Focus of the lecture: Understanding what constitutes a species and the mechanisms of speciation.

Definition: A species is a group of organisms capable of interbreeding and producing fertile offspring.
Importance of fertile offspring: It's not enough to just have offspring, they must be fertile.

Liger: Offspring of a male lion and a female tiger; larger than parents but sterile.
Hybrids are produced by cross-breeding distinct species but result in reproductive dead ends.

Reproductive Isolation: Key requirement for speciation where two populations can no longer successfully mate.
- Post-Zygotic Isolation: Occurs after zygote formation. Example: Mules (donkey + horse), sterile offspring.
- Pre-Zygotic Isolation: Occurs before fertilization. Examples include:
  - Behavioral changes (e.g., different mating songs in birds).
  - Temporal changes (e.g., nocturnal vs. diurnal animals).
  - Geographic isolation (e.g., physical barriers like rivers).
Allopatric Speciation
- Caused by geographic separation.
- Example: Animals evolving differently on either side of a river.
- Natural selection plays a role; different environments drive trait propagation.
- Darwin's observation of finches in Galapagos Islands.
Sympatric Speciation
- Occurs without geographic separation.
- Example: Finches on Daphne Major island; isolation due to song differences.
- Rapid speciation observed by Peter and Rosemary Grant.

Dog Breeding: An example of artificial selection where humans select traits.
Despite differences, all dog breeds (e.g., corgis and greyhounds) are the same species.
Potential for interbreeding despite challenges like size differences.

Gene flow interruption leads to reproductive isolation and potential new species formation.
Dog breeds exhibit high genetic similarity preventing post-zygotic isolation.