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Chapter 18: Problem 30

While examining the human genome, you find a gene that is not homologous to any other organisms known to man. You conclude that this gene must be unique to the human species and could not have evolved from another organism. Would this discovery suggest that humans do not share a common ancestor with all other organisms on Earth? Explain your answer.

Short Answer

Expert verified
No, the discovery of a unique gene does not suggest humans do not share a common ancestor with other organisms.

Step by step solution

01

Understand the Discovery

A gene found in the human genome is not homologous to any known genes in other organisms. This suggests the gene might be unique to humans.
02

Define Homologous Genes

Homologous genes are genes inherited in two species from a common ancestor. Lack of homologous genes between humans and other organisms can be interpreted in different ways.
03

Consider Gene Evolution

Genes can evolve separately after a species divergence, resulting in unique genes that are not found in closely related species. The existence of a unique gene does not imply that the species lacks a common ancestor with others.
04

Address Common Ancestry

All known life forms share a common ancestor based on multiple lines of evidence, including genetic, fossil, and biochemical data. Finding a unique gene does not disprove this well-established scientific consensus.
05

Conclusion

While discovering a unique gene is intriguing, it does not challenge the concept that humans share a common ancestor with other organisms. The gene could have evolved after humans diverged from other species.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Homologous Genes
Homologous genes are genes that are shared by different species due to their inheritance from a common ancestor. These genes often perform similar functions in different species. For example, the gene that codes for hemoglobin in humans is homologous to the gene that codes for a similar protein in other mammals like cows or mice.
When we find a gene in the human genome that doesn't seem to have a homologous counterpart in other species, it might simply have evolved in a unique way after humans diverged from their common ancestors with other animals. In other words, even though the gene is unique to humans now, it doesn't mean humans don't share a common ancestor with other organisms.
Homologous genes are key pieces of evidence for evolutionary relationships, helping to trace how species have changed and diversified over time.
Gene Evolution
Gene evolution can result in the development of genes that are unique to a single species or a small group of species. This happens through several mechanisms:
  • **Gene Duplication**: A gene might be copied, and the copy can accumulate mutations that give it a new function.
  • **Genetic Drift**: Random changes can cause certain gene variants to become more common in a population over time.
  • **Natural Selection**:.New mutations might offer an advantage and become more prevalent in the population.
These processes can lead to unique genes that are not found in closely related species.
When scientists find a gene in humans that is not homologous to genes in other species, it is often because this gene has evolved differently, not because humans don鈥檛 share a common ancestor with other life forms. This uniqueness adds to the diversity produced through evolution.
Common Ancestry
The concept of common ancestry is a cornerstone of evolutionary biology. Evidence from various scientific fields supports the idea that all life on Earth shares a single origin. This includes:
  • **Genetic Data**: DNA sequences show significant similarities among diverse species, indicating shared evolutionary paths.
  • **Fossil Record**: Transitional fossils show intermediary forms between major groups of animals, illustrating how species evolve over time.
  • **Biochemical Evidence**: Basic cellular processes and molecules, like ATP and ribosomes, are conserved across all life forms.
Discovering a unique gene in humans does not contradict this evidence. It鈥檚 likely that the gene either emerged after humans branched off from their ancestors or that it evolved so distinctly it no longer resembles its ancestral form.
Thus, the existence of a unique gene in humans is an expected outcome of evolutionary processes, not a refutation of common ancestry. We remain closely linked to the broader tree of life through shared genetic heritage.

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Most popular questions from this chapter

The selective breeding of plants and animals that possess desired traits is a process called artificial selection. For example, broccoli, cabbage, and kale are all vegetables that have been selected from one species of wild mustard. How is artificial selection both similar to and different from Darwin鈥檚 conception of natural selection? Does artificial selection provide evidence for evolution by natural selection? Explain. a. Both artificial selection and natural selection are the differential reproduction of individual organisms with favored traits. In artificial selection, humans have actively modified plants and animals by selecting and breeding individuals with traits deemed desirable. In natural selection, the most successful individuals in a species are selected by the species to reproduce b. Both artificial selection and natural selection are processes that result in better-adapted individuals within a species. In artificial selection, humans have actively modified plants and animals by selecting beneficial genes from other organisms and inserting them into the target organisms. In natural selection, natural processes such as mutations and viruses introduce new genes to a population c. Both artificial selection and natural selection are processes that cause organisms to be better adapted over time. In artificial selection, humans have trained animals to be more successful in completing tasks that the humans want completed. In natural selection, organisms train the functions that they will need to survive and reproduce d. Both artificial selection and natural selection are the differential reproduction of individual organisms with favored traits. In artificial selection, humans have actively modified plants and animals by selecting and breeding individuals with traits deemed desirable. In natural selection, individuals are selected naturally as its traits deem it more fit for survival and reproduction

Give an example of convergent evolution and explain how it supports the theory of evolution by natural selection. a. An example of convergent evolution is the development of the same function, swimming, in organisms that live in different parts of the globe, such as Arctic beluga whales and Antarctic right whales. The fact that organisms that do not come in contact with each other have developed the same traits suggests that natural selection can produce similar adaptations in organisms who share a similar environment b. An example of convergent evolution is the set of adaptations, such as better running speed or more efficient hunting, developed by a species in response to competition with a new species that moves into the same region. The fact that a species adapts after it comes into contact with a competitor suggests that natural selection works more quickly with higher selective pressures. c. An example of convergent evolution is the development of an ancestral structure, a limb, into two different modern structures, such as a hand and a flipper. The fact that natural selection can cause a structure to develop down two different pathways due to different environmental conditions supports the theory of evolution d. An example of convergent evolution is the development of the same function, flying, in organisms that do not share a recent common ancestry, such as insects and birds. The fact that wings that allow flight have developed from very different original structures suggests that the process of natural selection can produce similar adaptations in two very different types of organisms who share a similar environment

A friend says: 鈥淣atural selection is about the survival of the very fittest in a population. The fittest are those that are strongest, largest, fastest.鈥� Would you agree with that statement? Explain. What evidence from scientific disciplines can you offer to support your agreement or your disagreement? a. The statement is true. If an organism is not strong and fast, it will not survive long enough to reproduce and pass on its genes, and if it is not large and fitter than the other individuals around it then it will not be able to compete for a mate. Many seal species, for example, have only a single male who gets to mate. He must be the very fittest seal to win all the females. b. The very fittest organisms are not necessarily the ones that survive. Sometimes it is the least fit organisms that survive and reproduce. For example, in one generation the mice who are bad at foraging for seeds may reproduce prolifically and dominate the mice who are good at foraging. In this case, natural selection will select for the less-fit phenotype and spread it in the population. c. The definition of fitness is not correct. The strongest and fastest organisms are more fit than the weaker and slower ones, but large individuals are often at a disadvantage to smaller ones because they are easily spotted by predators. For example, a large rabbit will stick out on a field more than a small one and will get eaten by a hawk. d. What is meant by 鈥渇ittest鈥� is not necessarily strong, large, and fast. Fitness, as defined in evolutionary terms, has to do with survival and the reproduction of genetic material. For example, a small but showy male bird may be selected by female birds to reproduce, while a large but less colorful one is not.

Which is an example of an adaptation? a. The better nutrition of a human helps her grow taller. b. The webbed feet of a duck help it swim. c. The urban location of a raccoon helps it find food. d. The large leaves of a desert plant require more water.

In 1795, a Scottish geologist named Charles Hutton suggested that Earth鈥檚 geologic features could be explained by gradual processes that were still operating. This was in direct contrast to other scientific thought at the time, which included well-accepted proposals that geologic layers were representative of catastrophic events caused by processes no longer operating in the present time. Hutton proposed geologic features as the result of slow and consistent change, such as valleys formed by rivers wearing through rock. Hutton鈥檚 ideas were incorporated in the work of Charles Lyell, a geologist working in Darwin鈥檚 time. Lyell advocated a principle called uniformitarianism, the consistency of mechanisms of change over time. In other words, Lyell argued that the same geologic processes operating in the present had operated in the past, and at the same rate. The ideas of Hutton and Lyell influenced the work of Charles Darwin. How do Hutton鈥檚 and Lyell鈥檚 ideas connect to and provide support for Darwin鈥檚 theory of evolutionary change? a. The idea that the same processes that operate in the present also operated in the past, and at the same rate, supported Darwin鈥檚 hypothesis of natural selection because humans could select for desirable traits and produce change very rapidly, so natural selection would also be fast enough to produce the full range of diversity in living organisms. b. The idea that the same processes that operate in the present also operated in the past, and at the same rate, connects to Darwin鈥檚 hypothesis of natural selection because he had observed it happening in the present c. The idea that geologic change is the result of slow, continuous processes rather than sudden, substantial change connects to Darwin鈥檚 support of gradualism rather than punctuated equilibrium as the process that guided evolution. d. The idea that geologic change is the result of slow, continuous processes rather than sudden, substantial change connects directly to Darwin鈥檚 hypothesis that, given enough time, slow and subtle processes could produce substantial biological change.
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