Not a Fact Anymore

Not a fact anymore

Species are fixed, separately created forms that do not change into new species over time.

What we know now

Populations evolve across generations, species share common ancestry, and new species can arise when populations diverge genetically and reproductively.

Why it changed

Biogeography, fossils, comparative anatomy, selective breeding, and observations of variation supported common descent and natural selection. Genetics and molecular biology later supplied mechanisms and extensive independent evidence.

Status
Superseded
Category
Biology
Accepted approximately
Classical antiquity through the mid-19th century
Changed approximately
19th–20th centuries

Not every pre-Darwinian thinker believed species were absolutely fixed, and evolutionary ideas existed before 1859. The card refers to the dominant view among many European naturalists, not a universal belief across all cultures and periods.

Modern evolutionary biology continues to debate details such as rates, patterns, and mechanisms in particular cases, but common descent and population evolution are foundational findings.

Evidence

Sources and what they establish

Previous belief

Historical context

  • Evolution Darwin Correspondence Project, University of Cambridge

    Documents Darwin's private conclusion that species were not immutable and that related species descended from common stocks.

Current evidence

  • Evolution Resources National Academies of Sciences, Engineering, and Medicine

    Provides the National Academies' scientific resources on evolution and the evidence supporting common ancestry and evolutionary change.