2.5. Challenges to Darwin

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.

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.

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.

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.

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.