Question

Which of the following statements does NOT provide evidence supporting the common ancestry theory? (A) Scientists believe that of all the species on Earth that have ever existed, 99 percent of them are now extinct. (B) Many different animals have similar anatomical structures. (C) All organisms on Earth have a large percentage of their DNA identical to that of other species. (D) A lot of different animal species, including humans, start out looking the same as embryos.

Short answer

Statement A does not provide evidence supporting the common ancestry theory, as it focuses on extinction rates rather than shared ancestry. Statements B, C, and D all supply evidence in support of the common ancestry theory. Therefore, the correct answer is (A).

Step-by-step solution

Understanding the common ancestry theory

The common ancestry theory proposes that all living organisms on Earth share a common ancestor. Evidence supporting this theory includes similarities in anatomical structures, DNA sequences, and developmental patterns among different species. We need to evaluate each statement and find the one that does not support this theory.

Evaluating Statement A

Statement A says: Scientists believe that of all the species on Earth that have ever existed, 99 percent of them are now extinct. This statement discusses the extinction rate of species rather than providing evidence for a shared ancestry. So, this statement might not support the common ancestry theory.

Evaluating Statement B

Statement B says: Many different animals have similar anatomical structures. This statement relates to the concept of homologous structures, which are similar structures in different species due to shared ancestry. Since this statement suggests a connection between species through similarities in their anatomy, it supports the common ancestry theory.

Evaluating Statement C

Statement C says: All organisms on Earth have a large percentage of their DNA identical to that of other species. Genetic similarities among species can provide strong evidence for a shared ancestry. This is because closely related species will have more similar DNA sequences than more distantly related ones. Therefore, this statement supports the common ancestry theory.

Evaluating Statement D

Statement D says: A lot of different animal species, including humans, start out looking the same as embryos. This statement refers to the similarities in the early development of different organisms, which is evidence for common ancestry. Organisms sharing similar developmental patterns imply that they share a common ancestor. Thus, this statement supports the common ancestry theory.

Identifying the statement that does NOT support the common ancestry theory

From our evaluation of the statements, it is clear that Statement A does not provide evidence supporting the common ancestry theory, as it focuses on extinction rates rather than shared ancestry. Statements B, C, and D all supply evidence in support of the common ancestry theory. Therefore, the correct answer is (A).

Key concepts

Extinct Species

The theory of common ancestry is sacred in understanding the complexity and history of life on Earth. When we talk about extinct species, it's paramount to recognize that the vast majority of species that have ever existed on our planet are indeed no longer alive. While this fact by itself doesn't provide direct evidence for common ancestry, it sets the stage for a deeper investigation into the fossil record.

Through the study of fossils, scientists can unearth patterns of similarity among different organisms that have lived over the millennia. These patterns may indicate a progression from simple to more complex life forms, suggesting a common origin. However, the sheer fact of extinction doesn't inherently support the common ancestry theory, as it doesn't specify the relationships or genetic connections between species, living or extinct.

Anatomical Structures

Delving into the world of anatomical structures is like exploring a vast, intricate puzzle. Homologous structures are one of the most compelling pieces of evidence for common ancestry. These are structures that, although they may serve different functions, share a similar underlying anatomy and embryological origin among different species.

For example, the wings of a bat and the flippers of a dolphin are incredibly different in function, yet they share a structural blueprint that points to their evolution from a common ancestor. The presence of such homologous structures across a wide array of animals showcases the evolutionary modifications that have occurred over time, further cementing the concept of common ancestry.

DNA Similarities

Moving onto a microscopic scale, DNA similarities unfold a narrative of inheritance that links all forms of life. DNA is the blueprint of life, encoding the instructions that guide the development and functioning of organisms. When we observe that organisms share significant portions of their DNA, it's like finding chapters of a family story that are present in distant relatives' memoirs.

These genetic similarities, especially within essential genes, hint at a hereditary connection tracing back to a shared forebear. Moreover, the closer the genetic match between two species, the more recent their common ancestor likely existed. Thus, analyzing DNA is a profound method for confirming hypotheses about the relatedness of different species within the tree of life, fully supporting the common ancestry theory.

Embryonic Development

Embryonic development is a fascinating window into the past that can reveal evolutionary relationships. Many species, despite their vast diversity as adults, exhibit remarkably similar stages in their embryonic development. This phenomenon, known as embryological parallelism, is particularly evident in early stages where distinctions between species are minimal.

These similarities suggest that the development patterns of embryos are deeply conserved through evolution. It indicates that these organisms not only share an ancient, common ancestor but also retain the developmental processes that were present long ago. This evidence aligns beautifully with the common ancestry theory and bolsters the understanding of how seemingly disparate species are related at the most fundamental level of their existence.