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Look at the following pictures of a dolphin and a dogfish (Figure A4.1.8). Are these animals closely related? Which features may make you think that they are closely related?

Then think about what you know about the groups of animals they are in - are they in fact closely related? Which of the two would be more closely related to a human?

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Q3: Explain why it is important to use same method of classification throughout the scientific community?

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Q3: Explain why it is important to use same method of classification throughout the scientific community?

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It is important to use the same method of classification throughout the scientific community so that organisms like dolphins and dogfish are grouped accurately based on evolutionary relationships, not just appearance. Although dolphins and dogfish both live in the ocean and have similar body shapes (like fins and streamlined bodies), they are not closely related. A dogfish is a type of cartilaginous fish, while a dolphin is actually a mammal—more closely related to humans than to any fish. If scientists used only physical features like fins or aquatic habitats, they might wrongly classify dolphins as

Using a consistent, evolutionary-based method of classification (such as grouping organisms by common ancestors and genetic similarities) ensures that dolphins are correctly placed with mammals and dogfish with fish. This helps scientists communicate clearly, avoid confusion, and understand the true biology and evolutionary history of each organism. Without a standard system, scientists might interpret the similarity in appearance between dolphins and dogfish as a sign of close relation, which would be misleading.

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Taxonomy:

The science of classifying organisms is called taxonomy and it uses a hierarchical system to group organisms based on shared characteristics Taxonomic Rank | Dogfish (a type of shark) | Dolphin (e.g., Bottlenose Dolphin)

Kingdom | Animalia | Animalia

Phylum | Chordata | Chordata

Class | Chondrichthyes (cartilaginous fishes) | Mammalia (mammals)

Order | Squaliformes | Cetacea

Family | Squalidae | Delphinidae

Genus | Squalus | Tursiops

Species | Squalus acanthias (spiny dogfish) | Tursiops truncatus (bottlenose dolphin)

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Why should features that indicate common evolutionary origin be usedrather than superficial physical characteristics? Justify your answer using scientifically supported judgments.

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Why should features that indicate common evolutionary origin be usedrather than superficial physical characteristics? Justify your answer using scientifically supported judgments.

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Features that show a common evolutionary origin, like bone structure or genetics are more reliable for classifying organisms than traits like body shape.

In “On the Origin of Species” (1859), Darwin emphasised that shared ancestry is the key to understanding biological classification.

For example, dolphins and dogfish both have streamlined bodies, but they are not closely related.

In contrast, dolphins share key features with all mammals, showing they evolved from the same ancestor.

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the process by which distant related organisms independently evolve analogue traits due to similar selection pressure

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occurs when an ancestral species splits into

two reproductively isolated groups,

causing each group to develop different

traits due to their respective selective

pressures and natural selection

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1. Convergent Evolution:

This occurs when unrelated species evolve similar traits independently due to similar environmental pressures or lifestyles.

Example: Wings in birds, bats, and insects – they all developed flight, but not from a common winged ancestor.

2. Divergent Evolution:

This happens when related species evolve different traits and become more dissimilar over time, often due to adapting to different environments.

Example: Darwin’s finches – all evolved from a common ancestor but developed different beak shapes based on their food sources.

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Homologous Structures:

These are body parts that are similar in structure and position but may have different functions.

Example: The forelimbs of humans and bats – same bones, different uses.

Analogous Structures:

These are body parts that have similar functions but different structures and evolutionary origins.

Example: Wings of birds and insects – both used for flying, but built very differently.

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Shared Feature | Description

Aquatic habitat | Both live in the ocean (marine environments).

Streamlined body | Both have smooth, tapered bodies for fast swimming.

Fins | Both use fins to move and steer in water.

Tail (caudal fin) | Both have tails that help propel them forward.

Vertebrates | Both have a backbone (they’re in the phylum Chordata).

Carnivores | Both are meat-eaters – they hunt fish and other sea animals.

Well-developed senses | Both have strong senses (e.g., vision, hearing/smell).

Live in similar ecosystems | Both are part of the marine food web and are top predators.