{"id":9571,"date":"2026-06-01T21:33:48","date_gmt":"2026-06-01T21:33:48","guid":{"rendered":"https:\/\/kapdec.com\/help\/?p=9571"},"modified":"2026-06-01T21:33:48","modified_gmt":"2026-06-01T21:33:48","slug":"common-ancestry","status":"publish","type":"post","link":"https:\/\/kapdec.com\/help\/common-ancestry\/","title":{"rendered":"Common Ancestry"},"content":{"rendered":"

Unit : Natural selection<\/strong><\/h2>\n

Chapter: Common Ancestry<\/strong><\/h3>\n

Reference:<\/em><\/strong> Common ancestry, Homologous organs, Analogous organs, Fossils, Vestigial organs, Molecular Phylogeny, Homologous genes<\/em><\/p>\n

Learning objectives<\/strong><\/p>\n

    \n
  • To understand the fundamental molecular and cellular features shared across all domains of life, which provide evidence of common ancestry<\/li>\n<\/ul>\n

    Common ancestry<\/strong><\/p>\n

    Ancestral organism shared by two or more descendent lineages — in other words, an ancestor that they have in common. For example, the common ancestors of two biological siblings include their parents and grandparents; the common ancestors of a coyote and a wolf include the first canine and the first mammal.<\/p>\n

    Modern humans developed from their most common ancestor, Homo erectus, which means "upright man" in Latin, and arose in Africa during the last 200,000 years. Homo erectus was a human species that existed between 1.9 million and 135,000 years ago and is now extinct.<\/p>\n

    Homologous organs<\/strong> -those organs which have the same basic structure but different functions are called homologous organs.<\/p>\n

      \n
    • For example, the forelimbs of man, a lizard, a frog, a bird, and a bat seem to be built from the same basic design of bones, but they perform different functions.<\/li>\n
    • The forelimbs of a human are used for grasping, the forelimbs of a lizard are used for running, the forelimbs of a frog are used to prop up the front end of its body when at rest, and act as shock absorbers.<\/li>\n
    • Since the forelimbs of a human, a lizard, a frog, a bird, and a bat have similar structures but perform different functions, they are called homologous structures. This provides evidence that they are derived from a common ancestor<\/li>\n<\/ul>\n

      Analogous organs<\/strong> – those organs which have different basic structures but have a similar appearance and perform similar functions are called analogous organs.<\/p>\n

        \n
      • For example, wings of bats, wings of birds, wings of insects, etc. The wings of an insect and a bird have different structures but they perform the same functions, they are analogous organs.<\/li>\n
      • The presence of analogous organs indicates that even organisms having organs with different structures can adapt to perform similar functions for their survival under hostile environmental conditions.<\/li>\n<\/ul>\n

        Fossils<\/strong>– The remains of dead animals or plants that lived in the remote past are known as fossils. For example, a fossil bird called Archaeopteryx possesses features of both reptiles and birds. This concludes birds evolved from reptiles. There are various kinds of fossils like ammonite, trilobite, and dinosaur.<\/p>\n

        Vestigial organs<\/strong> are rudimentary. They have lost their function through evolution. For example, appendix in humans, muscles of ears, wisdom tooth, etc.<\/p>\n

        Molecular Phylogeny<\/strong><\/p>\n

        It is also evidence for evolution. According to this, changes in DNA during reproduction are the basic events of evolution. Organisms that are related to each other most distantly, will have greater differences in their DNA.<\/p>\n

        Example<\/strong><\/p>\n

        Amino acid sequences of proteins are compared to determine species' evolutionary histories. For instance, analysis of the amino acid sequence for beta–globin, a subunit of the protein haemoglobin, shows a single difference between humans and gorillas, but over twenty amino acid differences between humans and horses.<\/p>\n

        Homologous genes<\/strong><\/p>\n

        A homologous gene (or homolog) is a gene inherited in two species from a common ancestor. There are two types of homologous genes. Orthologs and paralogs are two fundamentally different types of homologous genes that evolved, respectively, by vertical descent from a single ancestral gene and by duplication. Orthology and paralogy are key concepts of evolutionary genomics.<\/p>\n

        Solved examples<\/strong><\/p>\n

        Example 1<\/strong>. The most recent shared ancestor of two different organisms\/people<\/p>\n

        a) Ancestor b) Evolution<\/p>\n

        c) Common Ancestor d) Homology<\/p>\n

        Solution 1<\/strong>: c. The most recent shared ancestor of two different organisms\/people is common ancestor.<\/p>\n

        Example 2<\/strong>. Similarities between organisms when they are Embryos (due to common ancestry and evolution)<\/p>\n

        a) Vestigial Structure b) Evolution<\/p>\n

        c) Developmental Homology d) Structural Homology<\/p>\n

        Solution 2<\/strong>: c. The similarities between organisms when they are Embryos (due to common ancestry and evolution) is called developmental homology<\/p>\n

        Summary<\/strong><\/p>\n

          \n
        • Ancestral organism shared by two or more descendent lineages — in other words, an ancestor that they have in common.<\/li>\n
        • Homologous organs -those organs which have the same basic structure but different functions are called homologous organs.<\/li>\n
        • Fossils- The remains of dead animals or plants that lived in the remote past are known as fossils.<\/li>\n
        • Vestigial organs are rudimentary. They have lost their function through evolution.<\/li>\n
        • Amino acid sequences of proteins are compared to determine species' evolutionary histories in molecular phylogeny<\/li>\n
        • A homologous gene (or homolog) is a gene inherited in two species from a common ancestor<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"

          Unit : Natural selection Chapter: Common Ancestry Reference: Common ancestry, Homologous organs, Analogous organs, Fossils, Vestigial organs, Molecular Phylogeny, Homologous genes Learning objectives To understand the fundamental molecular and cellular features shared across all domains of life, which provide evidence of common ancestry Common ancestry Ancestral organism shared by two or more descendent lineages — […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[629],"tags":[],"class_list":["post-9571","post","type-post","status-publish","format-standard","hentry","category-ap-biology"],"_links":{"self":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9571","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/comments?post=9571"}],"version-history":[{"count":0,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9571\/revisions"}],"wp:attachment":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/media?parent=9571"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/categories?post=9571"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/tags?post=9571"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}