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Ch. 25 - Phylogenies and the History of Life
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th EditionCh. 25 - Phylogenies and the History of LifeProblem 15
Chapter 25, Problem 15

Which traits do not correlate strongly with diversification rate within phyla but are likely to have been important in the original diversification of animal phyla during the Cambrian? Select True or False for each trait.
T/F presence of a head
T/F mobile lifestyle
T/F terrestrial lifestyle
T/F bilateral symmetry

Verified step by step guidance
1
Understand the context: The Cambrian Explosion was a period of rapid diversification of animal life approximately 541 million years ago. During this time, many major animal phyla appeared.
Consider the trait 'presence of a head': In the Cambrian, the development of a head (cephalization) was significant for the evolution of more complex organisms, but it may not correlate strongly with diversification rates within phyla today.
Consider the trait 'mobile lifestyle': Mobility was crucial during the Cambrian for survival and resource acquisition, but within phyla, diversification may not be strongly linked to mobility now.
Consider the trait 'terrestrial lifestyle': During the Cambrian, life was predominantly aquatic, so terrestrial adaptations were not relevant to the initial diversification of animal phyla.
Consider the trait 'bilateral symmetry': This trait was important in the Cambrian for the development of more complex body plans, but within phyla, it may not strongly correlate with diversification rates today.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cambrian Explosion

The Cambrian Explosion refers to a period approximately 541 million years ago when there was a rapid diversification of multicellular organisms, leading to the emergence of most major animal phyla. This event is significant because it marks a time of evolutionary innovation, where many new body plans and complex structures appeared, setting the stage for future evolutionary paths.
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Diversification Rate

Diversification rate in evolutionary biology refers to the speed at which new species form within a particular lineage or phylum. It is influenced by various factors, including environmental changes, genetic mutations, and ecological opportunities. Understanding diversification rates helps in studying how different traits may have contributed to the evolutionary success or failure of certain groups over time.
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Bilateral Symmetry

Bilateral symmetry is a body plan in which an organism can be divided into two identical halves along a single plane. This trait is significant in the context of the Cambrian Explosion as it allowed for more complex and efficient movement and sensory processing, which could have been advantageous in the early diversification of animal phyla. It is a common feature in many animal groups, indicating its evolutionary importance.
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Related Practice
Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria, but so few in others, such as Ctenophora? Based on your reading of this chapter, propose at least five traits that you think might have been most important in triggering diversification within phyla (examples: origin of hearing, origin of internal fertilization).

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? Jezkova and Wiens used a type of graph called a linear regression to find correlations between variables such as the proportion of species per phylum with legs (on the y-axis) and the diversification rate per phylum (on the x-axis). Sketch a graph to show what a strong positive correlation between these two variables would look like and what the absence of a correlation would look like.

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? A sample of Jekova and Wiens' results is shown here. The R2 value represents the strength of the correlation (where 0.00 is lowest and 1.00 is highest). The P value represents the statistical significance. Which five traits look most important?

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? The researchers know that correlation does not equal causation. However, can the absence of a correlation enable you to reject a hypothesis of causation? How would the R2 values be different in a scenario where a single trait was important to diversification in many phyla versus a scenario where different traits were important to diversification in different phyla?

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