The upper forelimbs of humans and bats have fairly similar skeletal structures, whereas the corresponding bones in whales have very different shapes and proportions. However, genetic data suggest that all three kinds of organisms diverged from a common ancestor at about the same time. Which of the following is the most likely explanation for these data?
a. Forelimb evolution was adaptive in people and bats, but not in whales.
b. Natural selection in an aquatic environment resulted in significant changes to whale forelimb anatomy.
c. Genes mutate faster in whales than in humans or bats.
d. Whales are not properly classified as mammals.

Verified step by step guidance

1. Identify the key concept: The problem is about evolutionary biology, specifically the concept of homologous structures and how they can evolve differently in different environments.
2. Understand homologous structures: Homologous structures are anatomical features in different species that originated from a common ancestor. They may have different functions but share a similar underlying structure.
3. Analyze the environmental influence: Consider how different environments can lead to different evolutionary pressures. In this case, whales live in an aquatic environment, which could lead to significant adaptations in their forelimb structure compared to terrestrial environments.
4. Evaluate the options: Option b suggests that natural selection in an aquatic environment led to changes in whale forelimb anatomy. This aligns with the concept of adaptive evolution, where organisms evolve traits that are advantageous in their specific environments.
5. Conclude with the most likely explanation: Based on the understanding of homologous structures and environmental adaptation, option b is the most plausible explanation for the observed differences in forelimb anatomy among humans, bats, and whales.

Key Concepts

Homologous Structures

Homologous structures are anatomical features in different species that originated from a common ancestor, reflecting evolutionary relationships. Despite differences in function, such as human arms and bat wings, these structures share a similar skeletal framework, indicating a shared evolutionary lineage. This concept helps explain why organisms like humans, bats, and whales have similar forelimb structures despite their diverse adaptations.

Natural Selection

Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce, leading to evolutionary changes over time. In the context of whales, natural selection in an aquatic environment could drive significant anatomical changes in their forelimbs, optimizing them for swimming. This concept is crucial for understanding how environmental pressures can lead to divergent evolutionary paths in species with a common ancestor.

Adaptive Evolution

Adaptive evolution refers to changes in organisms that enhance their survival and reproduction in specific environments. It involves the modification of traits through natural selection, resulting in adaptations like the streamlined forelimbs of whales for aquatic life. This concept explains why certain species, such as whales, exhibit significant anatomical differences from their terrestrial relatives, despite sharing a common ancestor.