7.6 Evidence of Evolution

Skills you’ll gain in this topic:

• Describe various types of evidence for evolution, such as fossil records and DNA sequences.
• Explain how anatomical and molecular similarities indicate common ancestry.
• Compare homologous and analogous structures to understand evolutionary relationships.
• Analyze fossil records and phylogenetic trees as tools for studying evolution.
• Relate different lines of evidence to the theory of evolution.

How Scientists Track Evolutionary Changes

Evolution is a scientific theory that is supported by a wide range of evidence from many different disciplines. Key pieces of evidence include:

1. Fossil evidence: The fossil record provides a historical record of the gradual changes that have occurred in organisms over time. This evidence supports the idea that species have evolved through time and that modern organisms have evolved from ancestral species.
2. Biogeography: The distribution of species across the Earth can provide clues about their evolutionary history. For example, similar species are often found in geographically close areas, while dissimilar species are found in distant areas.
3. Comparative anatomy and physiology: The similarities and differences in the anatomy and physiology of different species can provide clues about their evolutionary relationships. For example, the similarities between the bones of a bat's wing and a human arm suggest that they share a common ancestor.
4. Biochemistry and molecular biology: The similarities in the biochemistry and molecular biology of different species can provide clues about their evolutionary relationships. For example, the similarities in the genetic code of different organisms support the idea that all living organisms share a common ancestor.
5. Mathematical modeling: mathematical models help to understand how evolution can shape the patterns of genetic and phenotypic diversity observed in natural populations. In general, the evidence for evolution comes from many different disciplines, and it is strong and consistent. The theory of evolution provides a framework for understanding the diversity of life on Earth and how it has changed over time. In this section, we'll dive deeper into a couple of these disciplines and make comparisons to see how we got to the conclusion scientists have widely agreed upon today!

Fossils

Scientists have been able to date recovered fossils using a variety of methods. They can approximate the age of the rock surrounding the fossil to get a good idea of what era the fossil is from, use relevant geographical data (compared to other fossils found nearby), and even look at the decay of certain isotopes. 🧲

More details on some of the methods used to date fossils include:

• Stratigraphy: This method involves analyzing the layers of rock and soil in which a fossil is found to determine its age relative to other rocks and fossils in the same area. This can provide information about the era in which the fossilized organism lived.
• Radiometric dating: This method involves measuring the decay of certain isotopes, such as carbon-14 or potassium-argon, in the rock surrounding a fossil. This can provide a more precise age for the rock and, by extension, the fossil.
• Paleomagnetism: this method is based on the orientation of the Earth's magnetic field that fluctuates over time. By measuring the orientation of magnetic minerals in the rock, scientists can approximate the age of the rock and thus the fossil.
• Tephrochronology: By analyzing volcanic ash layers and their unique chemistry and mineralogy, scientists can match the ash from one location to another and use that information to build chronologies.
  

Source: Understanding Evolution

All these methods allow paleontologists to piece together the evolutionary history of an organism by comparing its age and characteristics with other fossils found nearby; they can also provide insights into the ancient ecosystems in which these organisms lived and how they evolved over time. Therefore, they are indispensable tools in understand the fossil record and help to support the theory of evolution.

Animals

Evidence of evolution can be found in today’s animals as well. Vestigial structures are structures in modern organisms that have lost most or all of their original function due to evolution. The human appendix, as well as wisdom teeth, body hair, tailbone and wings on flightless birds are examples of vestigial structures. 💸

The human appendix is a small pouch located at the beginning of the large intestine. It is believed to have once played a role in the digestive system of our ancestors, possibly as a fermenting chamber for cellulose-digesting bacteria, but in modern humans it has little to no function. Appendicitis, which is an inflammation of the appendix, can be a serious health concern but it is the only function that the appendix have in our bodies.

Wisdom teeth are a third set of molars that most humans have, but that often do not have enough room in the jaw to fully emerge. They are considered vestigial because they are not necessary for modern human diets and can cause problems if they do not emerge properly.

Body hair, similarly, is considered vestigial in humans. Humans have less body hair than other primates, and the hair that we do have is often not as thick or coarse as that of other primates, which is due to the loss of function over time, as humans evolved to better regulate body temperature with sweat glands rather than fur.

The tailbone, or coccyx, is the remnant of a tail found in other primates. It has lost most of its original function, but it still serves as the attachment point for some muscles and ligaments.

Wings on flightless birds are another example of a vestigial structure, as birds such as penguins, kiwis and ostrich have lost the ability to fly but still have wings. They are still used for other behaviors such as balance, courtship, and thermal regulation.

Source: ThoughtCo

All these examples indicate that a structure may not be necessary to survival in today’s environment but they have been inherited from ancestors who found them useful. They serve as a evidence of the change and adaptation in organisms throughout the evolutionary history. 😅

Homologous Structures

Homologous structures are structures or organs that are similar in form or function across different species and suggest a common ancestry. The comparison of the bone structure of the human arm, a dog's leg, a bird's leg and a whale's flipper is a great example of homologous structures. 🦵

In the case of the forelimbs of these animals, there are some notable differences, such as the bones being specialized for different types of movement, but there are also similarities in the basic structure, such as the presence of a humerus, radius and ulna. This similarity in structure indicates that these animals share a common ancestor who had a similar forelimb structure, and over time these structures evolved to adapt to the different environments and lifestyles of the descendants.

There's also evidence on a molecular level, such as DNA sequences and protein sequences, that can be used to compare the relatedness of different species. By comparing the sequences of similar genes across different species, scientists can determine if they share a common ancestor. This is one of the methods used to infer evolutionary relationships among species.

It is also important to note that all living organisms share a common genetic code, use the same set of amino acids to make proteins, and have similar processes for DNA replication. This is further evidence of the common ancestry of all living organisms, which supports the theory of evolution. 🧬

Source: WikiMedia Commons.

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