2.5. Challenges to Darwin

Overview of the Challenges to Darwin's Theory of Evolution

• Darwin's "Origin of Species" published in 1859 received both acclaim and criticism.

• Prominent scientists recognized its significance, but some criticized it for promoting atheism.

• Scientific objections were made, some of which Darwin addressed; others remain unresolved.

Major Objections to Darwin's Work

Objection 1: Complexity of Structures

• One key criticism was about the evolution of complex features (e.g., wings, human eye).

• Critics asked how natural selection could create such complexity, arguing that intermediate forms would not be adaptive.

• Darwin's Response: He suggested that even a partially developed structure (e.g., 5% of an eye) could be beneficial (e.g., light detection).

• Stages in Eye Evolution:

  • Simple Eyes: Seen in invertebrates like barnacles that can distinguish light and dark for feeding or predation.

  • Gradual Modifications: Eyes evolved into deeper, more cuplike forms to attract more light, ultimately leading to the more complex spherical eyes with lenses in vertebrates.

Objection 2: Intermediate Fossil Forms

• Critics pointed to the fossil record's gaps as a challenge to gradual evolution.

• Fossils often show long periods of stability followed by rapid changes, contradicting Darwin's idea of gradual change.

• Darwin's Prediction: He predicted that paleontologists would fill the gaps over time, which has occurred but not consistently in gradual ways.

• Fossilization is rare, contributing to the incomplete record, but many evolutionary transitions can still be traced.

• Example: Whale Evolution:

  • Research revealed transitional fossils indicating land mammals as ancestors.

  • Hippos are identified as whales' closest living relatives.

  • Transitional Lifestyle: Species like Ambulocetus may have existed between land and water environments, engaging in ambush predation.

Objection 3: Understanding Heredity

• Darwin struggled to explain heritable variation, which is key to evolution.

• He understood that individuals exhibit variation and that such traits could be passed to offspring, but lacked a mechanism to describe heredity.

• It wasn't until the 20th century when modern genetics provided clarity on heredity, solving one of the major criticisms of Darwin's theory.

Further Investigation Opportunities

• Resources available for deeper understanding of eye evolution through computer modeling.

• Descriptions of transitional fossils like Ambulocetus available through reputable sources such as the American Museum of Natural History.

• Engaging educational content (e.g., animated videos) designed for children to illustrate concepts like whale evolution.