Answer:
Claim: Dolphins and sharks share a recent common ancestor.
Counterclaim: Dolphins and sharks do not share a recent common ancestor.
Evidence:
1. Evolutionary history: Dolphins and sharks belong to different evolutionary lineages. Dolphins are mammals and are part of the order Cetacea, while sharks are cartilaginous fish and are part of the class Chondrichthyes. These two groups of animals diverged from a common ancestor over 400 million years ago, which is not considered recent in evolutionary terms.
2. Genetic evidence: Studies of the genomes of sharks and dolphins have shown that they have different genetic sequences and patterns, suggesting that they evolved separately and do not share a recent common ancestor. For example, a study published in the journal Nature in 2014 found that the genomes of sharks and dolphins have different patterns of gene duplication, which is evidence of independent evolution.
Reasoning: Based on the evidence presented above, it is unlikely that dolphins and sharks share a recent common ancestor. Although they share some similarities in their physical appearance and adaptations to aquatic environments, these similarities are likely the result of convergent evolution, where unrelated species evolve similar traits in response to similar environmental pressures. The evidence from evolutionary history and genetics strongly supports the counterclaim that dolphins and sharks do not share a recent common ancestor.
In conclusion, while dolphins and sharks may share some similarities, they do not share a recent common ancestor based on the available evidence from evolutionary history and genetics.
Step-by-step explanation:
Claim: Dolphins and sharks share a recent common ancestor.
Evidence: According to my research, dolphins and sharks do not share a recent common ancestor. In fact, their last common ancestor swam the seas some 290 million years ago ³.
Reasoning: Dolphins and sharks have many differences. For example, sharks have skeletons made of cartilage while dolphins have skeletons made of bone. Sharks use gills to get oxygen from the water in which they swim while dolphins go to the surface and breathe atmospheric air in through their blowholes. Sharks don't nurse their young while dolphins do ¹. These differences suggest that dolphins and sharks have evolved separately for a long time.
Conclusion: The claim that dolphins and sharks share a recent common ancestor is refuted by the evidence that their last common ancestor lived 290 million years ago and by the many differences between the two animals.