Biological Evolution and Evidence: Paleontology, Anatomy & Embryology

Biological Evolution and Evidence is substantial and persuasive. On Origin of Species, Darwin devoted a major amount of his work to identify patterns in nature that were consistent with evolution. Darwin believed that evolution might be explained by survival of species as a result of naturally occurring variety, a process he called "Natural Selection." As variations develop over generations, populations of creatures diverge from their ancestors.

Key Terms: Evolution, Macroevolution, Microevolution, Fossils, Anatomy, Paleontology, Anatomy, Embryology, Biogeography, Molecular Biology

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Evolution: Large Scale and Small Scale

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Evolution, in broad terms, is change in population's genetic composition (and, in many cases, heritable traits) through time. Based on size, biologists distinguish evolution into two categories: Macroevolution and Microevolution.

Macroevolution refers to changes that occur on a large scale over time, such as the emergence of new species or groups. Microevolution is a term used to describe small-scale changes in populations that affect just one or a few genes and occur over shorter durations. Microevolutionary processes can result in large-scale alterations that identify new species or groupings over thousands or millions of years.

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Evidence for Evolution

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Elements of biological evolution, including palaeontology, comparative anatomy, biogeography, embryology, and molecular biology, have been elaborated below:

Physical Evidence

Fossils

Fossils are preserved remnants or evidence of formerly existing species from distant past. Unfortunately, fossil record is neither full nor unbroken: most creatures do not fossilise, and ones that do are discovered by humans. Human-collected fossils, on the other hand, give unique insights into evolution over long periods of time. 

Fossils show a pattern of evolution and provide solid evidence that creatures from past are not the same as those living now. Scientists assess the age of fossils and classify them from around the world in order to identify when creatures existed in relation to one another. For example, horse lineage has yielded some of the most well-studied fossils.

Anatomy and Embryology

Evolution, according to Darwin, is a multigenerational process through which species change and give rise to new species. He postulated that life's evolutionary history is organised into a multi-level branching tree, with all species descended from a common ancestor.

Homologous Features

Two or more species that share a common physical trait, such as a complex bone structure or body form, may have derived it from a common ancestor. Homologous physical traits are those that are shared owing to evolutionary history (a common ancestor).

Whales, humans, birds, and dogs all have forelimbs that appear to be extremely different on the outside. This is because they have developed to work in a variety of conditions. When we examine forelimb's bone structure, we can observe that arrangement of bones is relatively similar across species. Rather than assuming such essentially identical characteristics emerged independently in each species, it is more plausible that bones were already present in a common ancestor of whales, humans, dogs, and birds.

Analogous Features

To make matters even more intriguing and difficult, not all physical similarities are evidence of common ancestry. Some physical features, on the other hand, are analogous: they arose independently in distinct creatures because they lived in comparable habitats or were subjected to similar selective forces. This process is termed as Convergent Evolution. 

For example, in the polar area, unrelated animals such as arctic fox and ptarmigan have been chosen for seasonal white phenotypes to blend in with snow and ice. These commonalities occur due to comparable selection pressures— advantages of not being spotted by predators—rather than common ancestry.

Analogous Structures

Embryology

Embryology, the study of an organism's development from its embryonic to adult form, also gives evidence of relatedness across previously disparate groups of species. Because genetic tinkering in embryo may have such dramatic implications in an adult, embryo development is often preserved. As a result, characteristics that are absent in other groups emerge in their embryonic stages before disappearing by the time they reach adult or juvenile form. 

Gill slits and tails, for example, can be seen in all vertebrate embryos at some point during development, including humans. These vanish in terrestrial adults but are preserved in aquatic adult species such as fish and some amphibians. Embryos of great apes, including humans, contain a tail structure that is gone by the time they are born.

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Biological Evidence

Biogeography

Throughout Geological time, distribution pattern of life on Earth follows patterns best characterised by evolution in conjunction with tectonic plate movement. Members of Proteaceae family can be found in Australia, southern Africa, and South America since they arrived before the split of Southern Supercontinent Gondwana.

Australia's abundance of marsupials and rarity of other mammals are a result of country's historical isolation. Endangered species (species found nowhere else) are common on islands walled off from rest of the world by large spans of water. Throughout time, these organisms develop into new species that are very different from their mainland ancestors. Although they share distant forebears with mainland species, Australia's marsupials, Galápagos Islands' finches, and other Hawaiian Island species are unique to their point of origin.

Molecular Biology

Similarities in biological molecules, such as structural homologies, might point to a shared evolutionary history. At their most basic level, all living beings have following characteristics:

• Similar genetic material (DNA)
• Similar genetic codes
• Similar process of gene expression (transcription and translation)
• Same molecular building blocks, such as amino acids

Molecular Biology

These characteristics suggest that all living things shared a common ancestor who had DNA as its genetic material, used genetic code, and expressed its genes via transcription and translation. Since they were "inherited" from ancestors, these features are shared by every living species.

Traits like having DNA or being able to conduct transcription and translation are useful for establishing how closely various species are connected, but they aren't as good for detecting how closely different creatures are related. Molecular features such as gene nucleotide sequences can be utilized to determine which organisms in a group are most closely related.

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Things to Remember

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• Analogous structures suggest that comparable selection forces may yield similar adaptations, whereas homologous structures give evidence for common ancestry (beneficial features).
• The relations of species can be determined by comparing and contrasting biological molecules (for example, the DNA sequence of genes).
• Biogeographical patterns reveal how different species are connected to one another.
• Although imperfect, the fossil record gives information on what animals existed at different points in Earth's history.
• Some populations, such as microorganisms and insects, develop over short periods of time and may be studied in real-time.

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