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history:evolution

evolution

the beginning of life

  • organic molecules such amino acids and fatty acids spontaneously form in a hot hydrogen rich reducing environment perhaps resulting in the spontaneous formation of fatty acid membranes in water combined with self-replicating “genetic” molecules (the early ones may not have been DNA/RNA or protein) which then could randomly mutate in the copying process.
  • It is likely that RNA evolved before DNA and this primordial RNA could then start creating proteins
    • nucleobases can assemble spontaneously, in a series of steps, from cyanide, acetylene and water
    • sugar molecules are easily formed in warmed alkaline solutions of formaldehyde, the ribose could be created by interaction of two simple sugars but as it is unstable in alkaline solution, it needs to be stabilised unless it is formed already bound to a nucleobase as below
    • schreibersite, a mineral commonly found in certain meteors, releases a form of phosphorus that is more soluble in water than phosphate and far more reactive with carbon-based compounds
    • when cyanide, acetylene and formaldehyde are mixed with the phosphorus, a readily vaporizable small molecule called 2-aminooxazole, which can be viewed as a fragment of a sugar joined to a piece of a nucleobase and it is possible that when the water evaporated, these molecules too could have evaporated to be deposited in a more concentrated area in a more purified form where they can combine to form full sugar and nucleobases and solar UV destroys any “incorrect” nucleotides to leave just C and U nucleotides. Perhaps there is a similar mechanism for the production of the G and A nucleotides.
    • these nucleotides then form chains when in the presence of clay suggesting that life may have formed in the clay rich muds of hot springs and experiments suggest RNA has the raw catalytic power to catalyze its own replication
    • the simple RNA protocell evolves
      • simple fatty acid membrane vesicles enclosing RNA and immersed in a solution of nucleotides will allow these to migrate into the cell and combine with the RNA to form a complimentary version of the RNA and the osmotic effects of these then pull water into the vesicle and, if there is fatty acids nearby to incorporate into the membrane, make it expand into tubular shapes which then break off into daughter vesicles
      • if these vesicles moved from cool to hot areas of a water pool, the sudden heat could cause the double strands of RNA to separate and then be used as templates for new strands hence reproduction
      • mutations would then result in improved chemicals such as ribozymes which would speed up the replication process and synthesize nutrients and eventually synthesis of proteins which they amazing potential actions and then would “learn” to make the more robust DNA 1)
      • it is possible that the 1st forms of “life” may have been self-replicating RNA “virus” particles (although there are other ways viruses may have evolved) 2)
  • the first bacteria
    • life is thought to have started on earth 4,280 mya

Archeozoic eon: 3,900-2,500 mya

  • sulphur oxidising and sulphate reducing bacteria
  • the “last” theoretical common ancestor of all life is called last universal common ancestor (LUCA) with and inferred set of 355 genes existed perhaps 3,500-3,800 mya which was anaerobic, CO2-fixing, H2-dependent with a Wood–Ljungdahl pathway (the reductive acetyl-coenzyme A pathway), N2-fixing and thermophilic. 3)
  • photosynthetic, oxygen producing cyanobacteria (“blue-green algae”) along with other microbes such as & archaens form microbial mats which over time become layered on a bed of calcium carbonates deposited from the carbon dioxide rich oceans (limestone) creating stromatolites start to oxygenate atmosphere

Proterozoic eon (2500 - 540 mya)

  • Great Oxygenation Event (GOE) 2400 mya
  • bacterial precursor of mitochondria
    • oxidase assembly machinery critical for the development of the inner membrane of mitochondria was present in these bacteria and has been preserved in evolution. OXA-dependent proteins are synthesized in the cytoplasm and then imported into mitochondrial organelles where they play important functions in cellular respiration, the exchange of metal ions and biochemical reactions 4)
  • anaerobic mitochondrial DNA
  • aerobic mitochondrial DNA (>1450 mya - perhaps in a Rickettsial bacteria)
  • mitosomes
  • hydrosomes
  • eukaryocytes evolve from endosymbiosis of procaryocytes with mitochondrial DNA creating complex cells oxidative mitochondrial capacity as well as anaerobic pathways (1,450 mya)
  • multi-celled organisms
    • Choanozoa (950mya)
      • Choanoflagellata
      • Animals (760mya) - nearly all animals have a dramatically shrunken mitochondrial gene count of only 13 protein coding genes the other thousands have been relocated into the host nucleus DNA 5)
        • Porifera (sponges)
        • Eumetazoa
          • Ctenophora (comb jellies)
          • Parahoxozoa (680mya)
            • Cnidaria (?741mya, but fossils dated to 580mya; corals, sea anemones, jellyfish)
              • Ediacaran soft-bodied fauna (610mya)
            • Placozoa
            • Bilateria (bilaterally symmetric body plan arose c650mya)
              • Xenacoelomorpha (lack a typical stomatogastric system; nervous system is basiepidermal, ciliated epidermis)
              • Nephrozoa (650mya; excretory organs and nerve cords - eg. early marine worms)
                • Protostomia (610mya) (the first opening (the blastopore) becomes the mouth)
                  • Ecdysozoa (529mya, “animals that moult”)
                    • Arthropoda
                      • Trilobites (521mya but extinct due to Permian extinction 252mya)
                      • Chelicerates (“have fangs”; horseshoe crabs, spiders (?420mya), mites, scorpions)
                        • Arachnida
                          • Araneae (spiders)
                            • Mesothelae (only one extant family)
                            • Opisthothelae
                              • Araneomorphae (fangs slope towards each other; 200-250mya; most modern spiders, most live < 1yr )
                                • Hypochilidae (lampshade spiders)
                                • Austrochiloidea
                                  • Gradungulidae (eastern Aust and NZ)
                                  • Austrochilidae (Chile, Argentina, Tasmania)
                                • Araneoclada
                                  • Haplogynae
                                  • Entelegynae
                                    • Theridiidae (tangle web / cobweb spiders incl. Lactodectus)
                                    • many more spider families
                              • Mygalomorphae (downward parallel fangs; 200-250mya; tarantulas, funnel-web, trapdoor spiders; females can live 25-45yrs)
                      • Myriapods (millipedes, centipedes)
                      • Crustacea
                        • malacostraca
                          • pericarida - amphipoda, isopoda (300mya)
                          • eucarida - decapoda (shrimp, prawns, crayfish, lobsters, crabs, etc)
                      • Hexapods (insects; 400mya)
                        • rapid diversification of flying insects 299-251mya
                        • now account for 75% of named animal species
                    • Nematoda (worms)
                  • Spiralia
                    • Gnathifera
                      • Rotifera
                      • Chaetognatha
                    • Platytrochotozoa (580mya)
                      • Platyhelminthes
                      • Lophotrochozoa (550mya)
                        • Mollusca
                        • Annelida
                • Deuterostomia (the first opening (the blastopore) becomes the anus)
                  • Ambulacraria (starfish)
                    • Echinodermata
                    • Hemichordata
                  • Chordata (notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail)
                    • Tunicata, (salps and sea squirts)
                    • Cephalochordata (small, segmented marine animals)
                    • Vertebrata (525mya)

Cambrian explosion of life (541mya)

  • fossils from 518mya at Chengjiang formation in China
  • a massive fossil find in 518mya old rocks on the bank of the Danshui river in Hubei province in southern China in 2019 has unearthed 4,351 separate fossils so far represent 101 species, 53 of them new to science, where well preserved primitive forms of jellyfish, sponges, algae, anemones, worms and arthropods with thin whip-like feelers, including 4cm long mud dragons and numerous comb jellies were entombed in an ancient underwater mudslide that swept them into deeper, colder water where they were buried in fine sediment halting the usual process of decay
  • fossils from the Burgess Shale, a 508m-year-old rock formation in Canada

Vertebrata

  • anamniotes (eggs laid in water)
    • cartilaginous marine vertebrates (fish the Devonian period is The Age of fish))
      • gnathostomes (jawed fish - evolved ability to convert nitrogen waste into urea which helped raise their blood osmolarity to that of sea water allowing migration to marine waters)
        • extinct Placoderms (armoured fish)
        • Acanthodians (cartilaginous fish, sharks, rays, skates and the extinct spiny sharks)
      • Osteichthyes (c420mya common ancestor of bony fish and developed a primitive air-breathing lung)
        • lampreys (developed a cough reflex to expel excess CO2), hagfish
        • Actinopterygii (bony fish)
      • Sarcopterygii (lobe-finned fish), air-breathing fish (ancient lobe-finned fish evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom. Some fish developed primitive lungs with new paired pulmonary arteries to help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen)
        • a small lobe-finned fish called Kenichthys (c395mya) evolved the beginnings of the internal nares / choanae which would allow air to move from the external nares to the lungs - the maxilla and premaxilla separated and an aperture—the incipient choana—on the lip in between the two bones. The paired fins had a build with bones distinctly homologous to the humerus, ulna, and radius in the fore-fins and to the femur, tibia, and fibula in the pelvic fins. These bony fish became the most numerous of all bony fish in the Devonian and most of the Carboniferous, although most were open-water fish, one group, the Elpistostegalians, adapted to life in the shallows. They evolved flat bodies for movement in very shallow water, and the pectoral and pelvic fins took over as the main propulsion organs, while they lost their median fins but the spiracle became large and prominent, enabling these fishes to draw air.
        • amphibia (c370mya)
          • tetrapod amphibia (c367mya)
            • Diadectomorpha (c330mya - large reptile-like amphibians - perhaps the 1st to walk on 4 legs)
            • Reptiliomorpha
              • amniotes (c312mya eggs fertilized within the mother or laid on ground)
                • sauropsids / reptilia
                  • Archelosauria
                    • Archosaurs
                      • Pseudosuchia (crocodilian)
                    • Testudeans (turtles)
                  • Lepidosauria
                    • sphenodon lizards (NZ)
                    • squamata / reptiles
                      • lizards
                        • Toxicofera (toxin venom producing reptiles evolved 200mya)
                          • Anguimorpha
                            • Varanus monitor lizards (112-65mya; 4-chambered hearts) eg. Megalania
                              • Mosasaurs (extinct marine reptiles 100-65mya)
                            • Anguidae (75mya; alligator lizards, glass lizards, etc.)
                            • Helodermatidae (Gila monster and Mexican beaded lizard)
                            • Shinisauridae (Chinese crocodile lizard)
                            • Xenosauridae (knob-scaled lizards)
                          • Iguanomorpha (190mya in India)
                            • Acrodonta including chameleons
                            • Pleurodonta – American arboreal lizards, chuckwallas, iguanas
                          • Ophidia
                            • Serpentes (snakes 120-150mya initially with legs but a trio of mutations in the enhancer of a gene known as Sonic hedgehog disrupt a genetic circuit that drives limb growth in snakes)
                              • Alethinophidia
                                • Madtsoiidae (extinct Gondwanian such as Australian Wonambi and Yurlunggur)
                                • Pythonoidea (4-chambered hearts)
                                • Boidae (4-chambered hearts; ovoviviparous snakes including boas, anaconda)
                                • Henophidia
                                • Caenophidia
                                  • “colubroid” snakes
                                    • colubrids
                                    • vipers
                                    • elapids 38mya
                                      • coral snakes (30-25mya)
                                      • Afro-Asian clade of cobras and mambas (30-25mya)
                                      • Australasian clade (Hydrophiinae) 25mya
                                        • Sea Kraits (Laticauda) 25mya
                                        • Australian terrestrial Elapids 20-25mya
                                          • viviparous sea snakes 16mya
                                            • hydrophiids 8mya
                                    • atractaspids
                                  • Acrochordids
                              • Scolecophidia (blind snakes)
                  • Avemetatarsalia (avian-like)
                    • Pterosauromorpha
                    • Dinosauromorpha
                      • dinosaurs (243mya)
                        • Sauropodomorpha (long-necked herbivore dinosaurs)
                        • Ornithischia (bird-hipped dinosaurs)
                          • birds
                            • Palaeognathae ⇒ ostrich, emu, cassowary, kiwi bird, moa, etc
                        • Theropoda
                • synapsids
                  • mammals
                    • monotremes c110mya (egg laying mammals)
                      • platypus
                      • echidna
                    • theria (not egg laying, retrovirus enabled syncytins proteins which allowed placentae, and lost the coracoid bone)
                      • eutherian mammals c161mya (amniotic sac surrounds the fetus, lack epipubic bones)
                      • metatherians c125mya in Asia (give birth to relatively undeveloped young)
                        • marsupials (?100mya in Utah) 65mya (young are carried in a pouch)
                          • Laurasian possums ⇒ North America ⇒ South America (connected to Nth America until 65mya)
                            • Ameridelphia (American marsupials - oppossums)
                            • Australidelphia (arose in Sth America, there is one species in Sth America, then migrated across a temperate Antarctica to Australia c55mya)
                              • Australian megafauna (now mostly extinct)
                              • kangaroos, wombats, Tasmanian devil, Tasmania tiger, etc

NB. In all animals, limbs are regulated by Hox genes, switch-boxes that control the expression of entire modules of genes at specified domains along the body axis.

history/evolution.txt · Last modified: 2019/03/22 00:27 by gary1