- The given below is the graphical representation of the changes in morphological features over a period of the geological time scale, where population A accumulates heritable
morphological features and give rise to distinct species B. Population B splits in to a distinct
species B2
Which of the following lineage represent the pattern of speciation by cladogenesis?
(1) Lineage 1
(2) Both lineage 1 and 2
(3) Lineage 2
(4) Neither of the lineage 1 and 2What is Cladogenesis?
Cladogenesis is the evolutionary process where a single lineage splits into two or more genetically independent lineages. This branching event leads to the formation of new species, each following its own evolutionary path. Cladogenesis is often triggered by factors such as geographic isolation, ecological shifts, or genetic divergence, and it is the main driver of the tree-like pattern of evolution seen in nature.
Key Features of Cladogenesis
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Branching Evolution: One ancestral species gives rise to two or more descendant species.
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Increase in Biodiversity: Each split increases the total number of species.
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Adaptive Radiation: Often associated with the rapid diversification of a lineage into multiple species, each adapted to different ecological niches.
Cladogenesis vs. Anagenesis
It is important to distinguish cladogenesis from anagenesis:
Feature Cladogenesis Anagenesis Pattern Branching (splitting of lineages) Linear (single lineage changes) Result Multiple descendant species One evolving species Biodiversity Impact Increases number of species No increase in species number Example Galapagos finches radiating into many forms Gradual change in a single lineage Interpreting Evolutionary Lineages
In graphical representations of evolutionary history—such as phylogenetic trees or lineage diagrams—cladogenesis is depicted as a branching point where one lineage splits into two or more.
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Lineage 1: If this lineage shows a split where population A gives rise to both species B and B2 (with B2 branching off from B), this represents a classic cladogenetic event.
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Lineage 2: If this lineage simply shows a gradual accumulation of changes in a single lineage without branching, it represents anagenesis, not cladogenesis.
Real-World Examples of Cladogenesis
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Galapagos Finches: A single ancestral species arrived on the islands and split into many distinct species, each adapted to a unique niche.
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Australian Marsupials: Geographic isolation led to the diversification of marsupials into a wide range of species.
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Cichlid Fishes in African Lakes: Rapid speciation events led to a remarkable diversity of species, all descended from a common ancestor.
Identifying Cladogenesis in the Given Scenario
In the scenario described, population A accumulates heritable morphological features and gives rise to a distinct species B. Then, population B splits into a distinct species B2. The key event that defines cladogenesis is the splitting of a lineage into two separate lineages, each capable of evolving independently.
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Lineage 1 represents this pattern: a branching event where one lineage (B) splits into two (B and B2). This is the hallmark of cladogenesis.
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Lineage 2 would only represent cladogenesis if it also shows a branching event, but based on the description, only Lineage 1 fits the definition.
Conclusion
Cladogenesis is the evolutionary process responsible for the branching patterns of life, leading to the vast diversity of species we see today. In graphical representations, Lineage 1—which shows a split from one ancestral population into two distinct species—best represents the pattern of speciation by cladogenesis.
Correct answer:
(1) Lineage 1 -
