The theory of evolution by natural selection was only gradually accepted…

The idea

Darwin and Wallace proposed evolution by natural selection in the mid-19th century, yet acceptance took decades. Three barriers explain the delay. First, the theory challenged the widely held religious belief that God created all species in their present form, so many people rejected it on faith rather than evidence. Second, the evidence available in 1859 was limited: Darwin had finches, fossils and artificial selection, but no direct demonstration of how variation arose or how traits passed to offspring. Third, the mechanism of inheritance was unknown; Mendel's work on 'units' was published in 1866 but ignored, and chromosomes were not linked to heredity until the early 20th century, roughly 50 years later. Without a mechanism, natural selection seemed incomplete. Acceptance grew as genetics, the modern synthesis and the fossil record provided supporting evidence.

What earns the marks

• State that the theory challenged the religious idea that God made all animals and plants, so it conflicted with accepted beliefs.
• Explain that evidence available when the theory was published was insufficient to convince many scientists.
• Explain that the mechanism of inheritance and variation was not understood until about 50 years after publication.
• Link the delay in acceptance to the later discovery of genes, chromosomes and DNA, which supplied the missing mechanism.
• Use the example of Darwin's finches or fossil evidence to show how evidence accumulated gradually.
• Recognise that scientific ideas are accepted when evidence and mechanisms support them, not immediately on publication.

Common mistakes and how to put them right

• Thinking the theory was rejected only because it was wrong.

  Put it right: It lacked a known mechanism of inheritance at the time.

• Believing Darwin published after Mendel.

  Put it right: Mendel's work came later and was itself unrecognised for decades.

• Assuming all scientists immediately accepted evolution.

  Put it right: Acceptance was gradual and involved religious and evidential objections.

Exam tips

• Name all three reasons in the statement and give a short explanation for each to secure full credit.
• Use the phrase 'mechanism of inheritance' when discussing the 50-year gap, and link it to genes and chromosomes.
• If asked why acceptance was gradual, structure your answer around religion, evidence and mechanism rather than writing a general history of Darwin.