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Evidence of Evolution

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Evidence of Evolution

The theory of evolution was and continues to be a highly controversial topic because it challenges so many spiritual beliefs. We will review the definition of evolution, then discuss different lines of evidence supporting the theory of evolution. We will also discuss what fossils and archaeological evidence tell us about human evolution.


Recap: What is evolution?

Evolution is a gradual and cumulative change in the heritable traits of a population of organisms.

It is mainly driven by natural selection, a process where individuals with traits that help them survive in their environment are able to reproduce more because of those traits. This change takes place over the course of many generations.

Examples of evidence of evolution

The theory of evolution is supported by a wide range of evidence including fossils, homology, molecular biology, biogeography, and direct observations. In this section, we will discuss each line of evidence and provide examples.

Fossils as evidence of evolution

Fossils are preserved remnants or traces of organisms from a past geologic age. Fossils provide evidence that life forms have changed over time and resulted in the diversity in life forms that we see today. Fossils show how organisms evolved, how new groups of organisms emerged, and how some species became extinct (Fig. 1).

Evidence of Evolution, great white shark evolved using transitional fossils, StudySmarter

Figure 1. This diagram shows how the great white shark evolved using transitional fossils. Source: Diagram is own work of uploader. Derived image authors from left to right: SaberrexStrongheart (CC-BY-SA) Meghunter99 (Public domain) Meghunter99 (Public domain) Meghunter99 (Public domain) Meghunter99 (Public domain), CC BY-SA, via Wikimedia Commons.

Fossils show patterns in the changes caused by evolution in different groups of organisms. For example, the pelvic bone in fossil stickleback fish consistently became smaller over time. The consistent shrinking of the pelvic bone is a pattern that suggests natural selection was the driving force behind the change.

Fossils also show how new groups of organisms emerge. For example, fossils provide evidence that cetaceans (an order of marine mammals that includes whales, dolphins, and porpoises) evolved from terrestrial mammals like hippopotamuses, pigs, and cows (Figs. 2-3). This is because fossils show that the pelvis and hind limb bones of extinct cetacean ancestors became smaller over time, eventually disappearing completely and developing into flukes and flippers.

Evidence of Evolution, Hippopotamus, StudySmarter

Evidence of Evolution, Whale, StudySmarter

Figures 2-3. Fossils show that the hippopotamus (left) is the closest living relative of the whale (right). Source (left): Diego Delso, CC BY-SA 4.0, via Wikimedia Commons. Source (right): Gabriel Barathieu, CC BY-SA 2.0, via Wikimedia Commons.

Homology as evidence of evolution

Similarities in the structure or development of different life forms (known as homology) also provide evidence of evolution because these show:

  1. How different species with similar structures can be traced back to common ancestors (divergent evolution)

  2. How different species with similar structures but no recent common ancestors were subjected to common selection pressures (convergent evolution)

Divergent evolution is the type of evolution where a species changes over time and branches off into new distinct species.

Species that share a recent common ancestor can have homologous structures: similar structures shared by closely related species. Homologous structures appear similar but serve different functions (Fig. 4).

For example, vertebrates like pigs, birds, and whales have forelimbs with the same basic composition that came from a common ancestor. Their forelimbs changed over time to serve different purposes that suit their present environment.

Evidence of Evolution, the relationship of bones in the forelimbs of humans dogs birds and whales, StudySmarter

Figure 4. This diagram shows the relationship of bones in the forelimbs of humans, dogs, birds, and whales. Source: Волков Владислав Петрович, CC BY-SA 4.0, via Wikimedia Commons.

On the other hand, species that are not closely related have also evolved with similar physical characteristics due to common selection pressures. This process is called convergent evolution. For example, birds, bats, and pterodactyls all have wings that can be used for flight even though they are not closely related (Fig. 5).

Evidence of Evolution, wings of birds bats and pterodactyl, StudySmarter

Figure 5. Birds, bats, and pterodactyl have similar structures with the same function--they have wings that they use to fly--but are not closely related. Source: John Romanes (1848-1894), Public domain, via Wikimedia Commons.

Molecular biology as evidence of evolution

All life forms share the same genetic material. From bacteria to humans, all life forms have DNA, as well as its mechanism for replication and expression (Figs. 6-7). This suggests that all species came from a very distant common ancestor.

Evidence of Evolution, Bacteria, StudySmarter

Evidence of Evolution, old man, StudySmarter

Figure 6-7. Bacteria (left) and humans (right) have DNA as their genetic material. Source (left): Mark Amend - NOAA Photo Library, Public domain, via Wikimedia Commons. Source (right): Reinhold Möller, CC BY-SA 4.0, via Wikimedia Commons.

Biogeography as evidence of evolution

We can also observe patterns in the geographic distribution of life forms on Earth (a branch of biology called biogeography). These patterns can be explained by evolution alongside the movement of tectonic plates.

For example, members of the plant family Proteaceae are found in Australia, southern Africa, and South America, which are all distant from each other. The presence of Proteaceae in these areas can be explained by their descent from a common ancestor that existed in the supercontinent Gondwana before it broke up into different landmasses (Fig. 8).

Evidence of Evolution, illustration depicting continents Laurasia-Gondwana, StudySmarter

Figure 8. An illustration depicting continents Laurasia-Gondwana dating back to 200 million years ago. Source: Lennart Kudling, CC BY 3.0, via Wikimedia Commons.

Evolution can also explain why islands tend to have many endemic plant and animal species. Endemic species are native to a specific geographical area and do not occur naturally elsewhere. Darwin proposed that species from the nearest mainland colonized islands and eventually evolved into new species as they adapt to their environments. The finches on the Galapagos Islands are an example of this.

Direct observations as evidence of evolution

Evidence of evolution can also be observed directly in species with fast reproductive cycles, such as bacteria.

For example, when bacteria are exposed to antibiotics, individuals with no resistance quickly die off. Individuals with resistance to the antibiotic are able to survive and reproduce. Then, resistant traits are passed on to more individuals in the population. Eventually, the population becomes more resistant to antibiotic treatment.

Evolution by natural selection can also be observed in species that evolve as a response to introduced species in their environment. An example of this is the different beak lengths of the soapberry bug which evolved according to the available food source. In Southern Florida, soapberry bugs feed on the seeds of the native balloon vine. In Central Florida, balloon vines (Fig. 9) have become rare, so soapberry bugs shifted to the seeds of the golden rain tree (Fig. 10)–an introduced species—as their food source.

Evidence of Evolution,  seeds of the balloon vine fruit, StudySmarter

Evidence of Evolution, seeds of the golden rain tree fruit, StudySmarter

Figures 9-10. The seeds of the balloon vine fruit are farther from the surface than the seeds of the golden rain tree fruit (right). Source (left): H. Zell, CC BY-SA 3.0, via Wikimedia Commons. Source (right): Art Davis, CC BY-SA 4.0, via Wikimedia Commons.

Soapberry bugs can feed more effectively when their beak is long enough to reach the seeds within a fruit. Because seeds of the golden rain tree fruit are closer to the surface than the seeds of the balloon vine, soapberry bugs that feed on the seeds of the golden rain tree have shorter beaks. In Louisiana, Oklahoma, and Australia, soapberry bug populations feed on introduced plants that have fruits larger than those of the balloon vine. In these areas, soapberry bugs evolved to have longer beaks.

Is there evidence of human evolution?

Humans are Homo sapiens, a primate species that walks upright and has a large, complex brain with a capacity for the use of tools, language, symbolic expression, and culture. Fossilized bones revealed the physical appearance of early humans and how they changed over time. On the other hand, tools, pottery, jewelry, and other archaeological evidence show the activities of early humans.

Evidence shows that humans first emerged in Africa. Bipedalism in humans evolved over 4 million years ago, while other traits like the use of tools and symbolic expression emerged only tens of thousands of years ago.

Homo sapiens is the last living species of the zoological tribe Hominini. Fossils show that our species once existed alongside another species of Homo, the Neanderthals (Fig. 11). Fossils and genetics also show that we and other species of Homo are closely related to and share a common ancestor with other Great Apes, like chimpanzees and gorillas.

Evidence of Evolution, neanderthal man, StudySmarter

Figure 11. Using fossils and archaeological evidence, we are able to reconstruct what a Neanderthal man could have looked like. Source: Jakub Hałun, CC BY-SA 4.0, via Wikimedia Commons.

Evidence of Evolution - Key takeaways

  • The theory of evolution is supported by a wide range of evidence including fossils, homology, molecular biology, biogeography, and direct observations.
    • Fossils show how organisms evolved, how new groups of organisms emerged, and how some species became extinct.
    • Homology shows how different species with similar structures can be traced back to common ancestors and how different species with similar structures but no recent common ancestors were subjected to common selection pressures.
    • All life forms have DNA which suggests that all species came from a very distant common ancestor.
    • Some patterns in the geographic distribution of life forms can be explained by evolution alongside the movement of tectonic plates.
    • Evidence of evolution can be observed directly in species with fast reproductive cycles and in species that evolve as a response to introduced species in their environment.
  • Fossilized bones and archaeological evidence give us insight into human evolution.

Final Evidence of Evolution Quiz

Question

What are fossils?

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Answer

Fossils are preserved remnants or traces of organisms from a past geologic age.

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How do fossils provide evidence of evolution?

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Answer

Fossils provide evidence that life forms have changed over time and resulted in the diversity in life forms that we see today. Fossils show how organisms evolved, how new groups of organisms emerged, and how some species became extinct.

Show question

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What is homology?

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Homology refers to similarities in the structure or development of different life forms.

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What do homologous structures imply?

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Different species with homologous structures can be traced back to common ancestors.

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Vertebrates like pigs, birds, and whales have forelimbs with the same basic composition. What does this tell us about evolution?

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Due to evolution, the forelimbs of vertebrates have changed over time to serve different purposes that suit their present environment.

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Why do some distantly related species have similar physical characteristics?

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Different species with similar structures but no recent common ancestors were likely subjected to common selection pressures.

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What genetic material do all life forms like bacteria and humans share in common?

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All life forms have DNA.

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How does biogeography provide evidence of evolution?

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Evolution best explains some patterns in the geographic distribution of life forms. These patterns include the presence of a related group of organisms in geographically separated areas and the endemism of island species.

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How does endemism in island species provide evidence of evolution?

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Endemic species show how mainland species evolved into different species after colonizing islands and adapting to their environments.

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True or false: evolution cannot be observed directly as it takes place over generations.

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False. Evidence of evolution can also be observed directly in species with fast reproductive cycles such as bacteria.

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True or false. There is evidence of human evolution.

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True. Fossilized bones and archaeological evidence give us insight into human evolution.

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Where did humans (Homo sapiens) first emerge?

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Africa

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How did endemic island species evolve from mainland species?

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Endemic species are usually related to the nearest mainland species. The nearest mainland species likely colonized these islands and eventually evolved into new species after adapting to their environments.

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Question

How do bacteria evolve?

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When bacteria are exposed to antibiotics, individuals with no resistance quickly die off. Individuals with resistance to the antibiotic are able to survive and reproduce. Then, resistant traits are passed on to more individuals in the population. Eventually, the population becomes more resistant.

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Question

What are examples of evidence supporting the theory of evolution?

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The theory of evolution is supported by a wide range of evidence including fossils, homology, molecular biology, biogeography, and direct observations.

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What are layers of sedimentary rocks called?

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Strata

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What does the position of fossils in the sequence of sedimentary strata tell us?

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The relative age of fossils

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What is the fossil record?

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The fossil record is the documentation of the history of life on Earth based primarily on the sequence of fossils in sedimentary strata.

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How does radiometric dating measure the age of fossils?

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Radiometric dating estimates the ages of fossils by measuring the decay of radioactive isotopes. 

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How are decay rates usually expressed?

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Half life

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What is a half-life?

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The time it takes for half of the original isotope to decay into a new isotope

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How is the decay rate of an isotope calculated?

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The decay rate of an isotope is calculated by measuring the number of decayed isotopes in the sample then determining the ratio between the original and decayed material.

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How can radiometric dating be used to infer the age of fossils?

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Radiometric dating can also be used to infer the age of fossils by sampling surrounding layers of volcanic rock.

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How did Darwin use the fossil record as evidence for evolution?

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Darwin showed that at different points in geologic time, different species emerged as the traits of pre-existing species gradually changed.

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What are the earliest life forms on Earth?

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The fossil record shows that 3.5 billion-year-old microbial mats of cyanobacteria that lived in hot springs and hydrothermal vents are the earliest life forms on Earth.

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What did the microbial mats produce that made it possible for other life forms to emerge?

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The microbial mats produced oxygen which allowed other life forms to emerge.

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What is a mass extinction?

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Mass extinction is an event where over half of the extant species seem to have suddenly disappeared.

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Why is the fossil record incomplete?

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Many organisms were not preserved as fossils because they did not die under the right conditions for fossilization, while those preserved as fossils may have been destroyed or are yet to be discovered.

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What does the fossil record document?

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The fossil record documents the history of life on Earth.

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What are fossilized microbial mats called?

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Fossilized microbial mats are called stromatolites.

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What is homology?

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Homology refers to similarities in traits and features because of common ancestry.

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What is morphological homology?

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Morphological homology is when different species have similar structures with the same basic form because of common ancestry.

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What are homologous structures?

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Homologous structures are structures that appear similar and can be traced back to common ancestors but serve different functions due to evolution.

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Vertebrates like pigs, birds, and whales have forelimbs with the same basic composition which can be traced back to a common ancestor.  What type of homology does this demonstrate?

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Morphological homology

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Kangaroos, wombats, and koalas all use external pouches to raise their newborn offspring. This feature can be traced back to one common ancestor. What type of homology does this demonstrate?

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Morphological homology

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What is morphology?

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Morphology is the study of the structure and form of organisms. 

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Besides structure and form, where can similarities in organisms be found?

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Besides structure and form, similarities also occur in the genetic code and in the developmental stages of organisms.

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What are the three types of homology?

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The three types of homology are morphological, molecular, and developmental.

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What is molecular homology?

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Molecular homology is when different species have similar genes or other DNA sequences that were inherited from a common ancestor.

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Some closely-related species have very similar genes even if they do not resemble each other. This is an example of what type of homology?

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Molecular homology

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What is developmental homology?

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Developmental homology is when different species have similar structures in various stages of development.  

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What is the difference between morphological and developmental homology?

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In morphological homology, similarities appear in the structure and form of the species. In molecular homology, similarities appear in the genes or DNA sequence of the species.

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All vertebrate embryos have gill slits and tails but these disappear by the time they are born. This is an example of what type of homology?

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Developmental homology

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Why is it important to distinguish between analogous and homologous traits?

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Scientists focus on homologous traits when reconstructing phylogenetic trees because only homologous traits show the evolutionary relationships among organisms.  

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What are phylogenetic trees?

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Phylogenetic trees are visual representations of the evolutionary relationship among organisms.

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What does common ancestry mean?

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Common ancestry means having descended from one ancestor.  

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What does sharing a recent common ancestor imply about the evolutionary relationship of two or more species?

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Sharing a recent common ancestor means that two or more species are closely related.

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If two or more species do not have a recent common ancestor, what does it imply about their evolutionary relationship?

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Not having a recent common ancestor means that two or more species are distantly related. 

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Why do we say that species are distantly related instead of unrelated?

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We say that species are distantly related because it is believed that all life forms can be traced back to one common ancestor.  

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Why do similarities imply relatedness among species?

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Similarities imply relatedness because it is likely that traits and features shared by a group of organisms were inherited from a common ancestor.

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