Speciation

Alfred Russel Wallace and Speciation

Goal: Understand Wallace’s contribution to evolution and how new species form.

1. Alfred Russel Wallace

• Wallace was a contemporary of Darwin.

• Traveled widely, studying plants and animals.

• Interested in warning coloration (e.g., bright red frogs signal toxicity).

• Independently proposed evolution by natural selection.

• In 1858, Wallace and Darwin jointly published their findings.

• In 1859, Darwin’s On the Origin of Species presented natural selection to a wider audience.

2. Speciation (Formation of New Species)

• Wallace studied how new species form → process called speciation.

• Often involves geographical barriers (e.g., rivers, mountains) separating populations.

Example: Snails on an island

1. Initial population: One species of snails, all can interbreed. Beneficial mutations spread through the population.

2. Geographical barrier: A river separates the population into two groups.

3. Independent evolution:

   • Different alleles favored in each population (natural selection).

   • No interbreeding → mutations cannot spread between populations.

4. Reunion after many generations:

   • Populations are now phenotypically different.

   • They cannot produce fertile offspring → now considered two different species.

Key point:

• Speciation requires a geographical barrier to separate populations and prevent interbreeding.

✅ Key Takeaways

• Wallace contributed to natural selection independently of Darwin.

• Speciation occurs when populations evolve separately and cannot interbreed.

• Geographical isolation is a major driver of speciation.