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Lecture 4

Biology 1001A Lecture 4.pdf

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Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 4 Biodiversity –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– - on average, 15 thousand species are catalogued each year - Charles Darwin suggested that all life came from a common ancestor How many species? - there is very little agreement about this - some say as little as 3 million - some say as many as 100 million - a recent study estimates the number at 8.5 million - only about 1.3 million species have scientific names Similarities due to descent from a common universal ancestor - almost everything on earth uses the same genetic code, therefore all life on earth has at least some similarities to each other - there is only one LUCA - there are many MRCAs (most recent common ancestors) Reverse tour of evolutionary history - start at present day and climb down the tree of life - 8.7 million other species doing the same thing - branching points on tree of life –> rendezvous points - at each point, meet other species, and the group’s MRCA (“concestor”) Rendezvous Zero MRCA of all humans - all people in this room share a common ancestor - going back far enough, everyone would have a common ancestor Rendezvous 1: Chimps and Bonobos - if we are descended from chimpanzees, why are there still chimpanzees still around? - we are not descendent from chimpanzees, we are cousins of the chimpanzees - humans are not descendent from chimpanzees, humans and chimpanzees are both descendent from a common ancestor - the common ancestor was probably closer to chimps than humans Rendezvous 2 Gorillas - 7 million years ago, we would find our most recent common ancestor is the African great ape Rendezvous 3: Orang utans - 14 million years ago - orang-utans gave rise to the African great apes - this is the MRCA of all great apes Biology 1001A | 2012 Rendezvous 4: Gibbons - smaller, and more athletic than other species Rendezvous 5,6: Old World & New World monkeys - 25 million years ago - 25 species of old world monkeys - Rendezvous 6: 40 million years ago, new world monkeys Rendezvous 7: Tarsiers - 58 million years ago - only about 5 species remaining Rendezvous 8: Lemurs and Lorises - 63 million years ago - 50 species - MRCA of all primates End-Cretaceous mass extinction, 65 million years ago - global disaster which resulted in the extinction of dinosaurs - catastrophe resulted in mass extinction of about half the species on Earth Rendezvous 10: Rodents & Rabbits - more than 2000 species of rodents - over 40% of all mammals are some type of rodent - very successful at survival, hence they are still around today Rendezvous 11: Laurasiatheres - bats, Insectivora, Carnivora, perissodactyls - laurasiatheres evolved in the north - hippos and whales are actually very closely related - canines and cats Rendezvous 14: Marsupials - now are largely restricted to Australia - convergent evolution Rendezvous 15: Monotremes - egg laying mammals - duck billed platypus - MRCA of all mammals Rendezvous 16: Reptiles - many reptiles are more closely related to birds than they are to other reptiles - birds are actually reptiles Now The Rest of the Vertebrates Biology 1001A | 2012 Rendezvous 17: Amphibians - MRCA of all tetrapods 340 mya Rendezvous 18: 18-22 - Lungfish, coelacanths, ray-finned fish, sharks, jawless fish - these “fish” are no more closely related to each other than they are to us - MRCA of all vertebrates 530 mya Rendezvous 26: Protostomes - greater than one million described species - to a first approximation, all animals are insects - there are over one million species of protostomes Rendezvous 34, 35, 36: Fungi, Amoebozoans, Plants - now we are not even looking at animals - we are more closely related to fungi than we are to plants - multi-cellularity has evolved more than once Rendezvous 38: Archaea - adaptions to extreme environments - we are more closely related to archaea than we are to bacteria Rendezvous 39: Bacteria - we go all the way back to LUCA for this - humans are most distantly related to the bacteria, not the archaea Summary: Diversity of Life - we can learn a lot by tracing descents of organisms - reconstructing patterns of relatedness, and even estimating number of species, is challenging - even estimating numbers of species is very difficult and there is much disagreement and uncertainty - some similarities reflect shared ancestry; other traits similar due to convergence (ex. eyes, sonar) - if evolution were to be rerun, would the outcomes be the same? - would evolution still result in a race of human like organism who sit in lecture and discuss their own ancestry? ______________________________________________________________________ Notes on Recommended Readings Evolution: Principles and Processes, Chapter 8 (not Box 8.1) Key Concepts - the first organisms may have been single-celled methane producing bacteria that existed more than 3.5 bya (billion years ago) Biology 1001A | 2012 - the earliest know fossils are single celled cyanobacteria that deposited stromatolite reefs 3.5 bya - both methanogens and cyanobacteria modified earth’s atmosphere, leaving more oxygen and less carbon dioxide - organisms, speciation, and ecosystems are ancient, having arisen at least 3.5 bya - cells with nuclear membranes and organelles (eukaryotic cells) arose 2.5 bya - the ability to form organelles with specific functions was a major factor in the origin and diversification of eukaryotes - until about 50 years ago organisms were classified into two kingdoms, plants and animals - life was classified into prokaryotic and eukaryote domains about 50 years ago using cellular characters - about 30 years ago life was reclassified using molecular evidence into three kingdoms: eubacteria, archaea, and eukarya - although we can classify life into kingdoms, all organisms are connected by having shared a common universal ancestor and as branches of a universal tree of life - constructing a tree of life (which shows evolution) for cells with prokaryotic organization may be impossible because of horizontal gene transfer throughout the history of life Overview - all organisms, no matter how we name, classify or arrange them on
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