Summay/notes on the The Greatest Show on Earth by Richard Dawkins Preface: Watch the three episode series "The Genius of Charles Darwin" from Channel 4, 2008 Chapter 1 - Only a theory Dawkins discusses here, what a theory is and what is mean by the theory of evolution. 40% of americans deny that humans evolved from other animals and think that we were created by god within the last 10000 years. Influencial philosophers tell us we can't prove anyting in science. Mathematicians are the only ones that can strictly prove things. In science, things are just facts, that evidence confirms and that have never been disproven. A conjecture is a proposition that looks true but has never been proved, it becomes a theorem once proved. Example: The Goldbach Conjecture states that any even integer can be expressed as the sum of two primes. Dawkins calls the theory of evolution a "theorum", something that cannot be proved like a mathematematical theorem. "Observations" are usually not enough. Psychological experiments have shown how little "eye-witness" testimony can be trusted. There is the famous Gorilla experiment, whne people watch a basketball film and look at the passes but they fail to see a Gorilla is crossing the scene. It is possible to make a distinction between the "fact" (or theorum) of evolution and the theory of what drives it. The differen theories are natural selection, or "Lamarck's theory of "use and disuse" and the "inheritance of acquired charactistics". Natural selection is most likely the predominant driving force. Chapter 2 - Dogs, Cows and cabbages. Dawkins states tha the discovery of evolution was held back by the dead heand of Plato. For Plate, the reality that we think we see is just shadows cas on the wall of our cave by the flickering light of the camp fire. A triangle drawn in the sand is just the shadow of the ideal essential triangle. The same can be said of the rabbits we see, they are flawed deviations of the "ideal" notion of raabit. The problem is that the definition of a species is not that easy. After tens of thousands of years, the rabbits may have evolved in another population with different traits. This evolution is continuous and the definition of a species is just representative of a given population at a given time. As the Greek philosopher Heraclitus said "all is fluid, nothing is fixed". Evolution of species can be shown by the artificial selection. Horiculturalists have changed the wild cabage Brassica oleracea, over few centuries, into :broccoli, cauliflower, kohlrabi, kale, Brussel sprouts, spring greens, romanescu and other cabbages. Similarly, all breeds of dogs are modified wolves: not jackals, not coyotes and nt foxes. Genes dont blend they shuffle. Populations don't get more boring. Each individual animal that we see in a population is a sampling of the gene pool of its time. There is no intrinsic tendency in gene polls for particular genes to increase or decrease in frequency. But when there is a systematic increase of decrease in the frequency of a particular gene in a gene poll, that's exactly waht is mean by evolution. All puppies have similar faces becasue they all need to suck and for this it's not advantageous to have a long snout. Often , the rates of growth of different parts of an animal bear some simple mathematcal relation. This was investigated by Sir Huxley in the 1930s. Chapter 3 - The primrose path to macro evolution To some extent, selecting breeding is also found in nature, where generations of ancestral flowers were chosen by generations of ancestral insects of hummingbirds or other natural pollinators. Moving pollen through wind is wasteful. Using animal is more efficient, flowers use nectar and colors to attract them. Nectar is a sugary syrup manufactured by plants specifically and only for paying and fuelling animal polenisators (bees, hummingbird, etc.). It's a balance for the flower, since it's costy to produce, also producing too much and there is no incentive for the insect to visit the next flower, too little and there is no incentive to visit. Colors may also be a way to attract. We should remeber that flowers may have more colors and patterns in the ultraviolet spectrum that we cannot see but insect can (e.g. the evening primrose). Some flowers look like bees to attract insects. A species of wasp stings spiders and lay eggs on them. The brassia spider orchid looks like a spider, to fool the wasps. There is an inverse case, where the pideer Epicadus heterogaster mimics an orchid so that insects come to t in search of nectar.. Canari birds are named after the islands. Galapagos Islands on the other hand comes from a spanish name for turtoise. The sounds of canaries male caues the femalse ovaries to swell and secrete hormones that bring them into reproductive condition. One could say that the male aremanipulating the females by singing to them. - Artificial selection: humans chose species for breeding based on some criteria. E.g. Belyev selection of foxes for tameness, which ended up behaving and looking like domestic dogs (black-white colors, ears down, tails up, six-month heat for females, sounds) - Sexual selection: chosing an attractive partners for breeding, preserving attractive genes - Natural selection: preserving attractive features but not deliberately. Non-random survival of randomly varying hereditary equipment. Individuals that are chosen by the fact that the happen to possess superiod equipment to survive are the most likely to reproduced and therfore to pass on the gnes for possessing superior equipment. Therefore, gene olls tends to become filled with genes for making superior survival and reproduction. Chapter 4 - Silence and slow time Dendrochronology dates things in time using wood ring patterns wichi match typical climates over the year. By comparing all the trees found it is possible to overlap those patterns all the way up to 11.500 years ago (the chain is not unbroken though). Radioactive-decay clocks. Sodium 24 turns into magnesium 24 when a neutron turns into a proton. Other decays involve the opposite process. Some decays involve the ejectin of alpha-particle (two-protons and two-neutrons). The radioactive isotope Uranium-238 decays to thorium-234. The rate of all these decay is exponential: a fixed proportion of whatever is left turns into the second element. Different elements have different half-cycles, ranging from billions of years to milliseconds. Assuming there was none of the second element at the origin, and knowing the proportion of both elements and the half-life, it is possible to date when the sample was formed. When volcanic rocks solidifies there is potassium-40 in it but no argon, this is the "zero" origin of the clock. This solidification is rather fast. this cannot be done for sedimentary rocks. Carbon has a remarkable capacity for forming chains and rings and complex molecular architecture. One atom in a trillion of carbon is carbon-14, continuously being made by cosmic rays ejecting neutrons from atoms in the atmosphere. A Nitrogen nuclei (7-7) stroke by a neutron, converts one of the protons in the nuclei into a neutron, becoming Carbon-14 (6-8) . Plant biochemistry doesn't care between carbon-12 and carbon-14, so carbon-14 is incorporated into the plant. All living creatures have the same ratio of carbon-12 to carbon-14, which is the one you'd find in the atmosphere. The carbon 14 clock is zeroed when the organism died and stop exchanging carbon with the atmosphere. Chapter 5 - Before our very eyes This chapter is about evolutions that are visible within a human life (elephant tusk, lezards from islands to islands, bacteria). Our appendix is a vestige of the larger caecum (an alley in the gut as aa fermentation chamber aided by bacteria to digest cellulose) in our more vegetarian ancestors. E. coli is a common bacteirum, we have about a billiion in our large intestine. Antibioticsare dosage dependent. A high dose will kill all the bacteria. An intermediate dose will not kill all and hence select in favour of genes for resistance, since there is genetic variation among bacteria, some more susceptible than others. Taking all the pills is important to avoid leaving behind semi-resisant bacteria. Chapter 6- Missing link There is no missing link. Ancestors of whales, dugongs, dolphins, penguins, crocodiles, otters, sea snakes, lived on earth and then returned back to the sea. They never developed gills again. Sea turtles extract oxygen from a pair of chambers at there rear end that are rich in blood vessels. An australian river turtle gets most of its oxygen by "breathing through its arse". Some turtles have even done the journey from water to earth to water to earth. Chapter 7 - Missing persons Homo Sapiens appeared about 100.000 years ago, and diversified into allthe races (!) that we see today: inuit, native americans, native australians, chinese, etc. It is a common misunderstanding: we are not descended from the chimpanzees, we have a common ancestor. The hole for the spinal cord (formane magnum) points downward for bipeds and backwards in quadrupeds. Lucy is 3M year old, is an Australopithec. It means southern ape (not relate to Australia, which means southern country). Naming is mileading though: it would be impossible to give discrete names if the fossil record were more complete. There is no such thing as the first specimen of a species. Any born specimen would be classified as the same species as its parents and its children.. There is no definite point where the term "man" ought to be used. Think of the difference between an adult and a teenager. Where is the true limit? It seems infant chimpanzees looks more like us. So humans may have retained juvenile characteristics into adulthood. Chapter 8 - You did it yourself in 9 months Changes occur dramatically during the embryological delevopment. DNA is not a blueprint, you can't reconstruct the DNA out of a body. There are only 20 kinds ofamino acid, and all proteins are chains made of these. A cell is a factory capable of creating a wide variey of substances depending on which enzyme is present in the cell, the presence of the enzymes being determined by the genes. Only few genes are activated in each cell. The acivation of certain gene is done via switch genes or controller genes which are influenced by the chemical environment of the cell. The composition of a protein determines its 3D shape and its function. The composition of cells are different thanks to asymmetric cellular division: the genes are the same but the chemical surrouding is different. So a mutation in a gene, may alter the composition and hence shape of a protein, which may then for instance acts as a catalyser that may speed up the growth of a given body part during the embryonic development. Natural selection favours the survival in the gene pool of the genetic mutations responsible for making crucial changes in embryos. The systme is the same in all animals, plants, fungi, bacteria, archae, viruses. Chapter 9 - The ark of the continents Life on earth would be boring without islands. Popoulations can't diverge if the keep interbreeding with each other. Islands let populations diverge so much that when and if they meet again, they can't interbreed anymore. The millions of species that have populated Earth have been possible thanks to the chance separation of two sub-populations of a species, often, on either side of a geographical barrier. Island gigantism and dwarfism: small anaimal on an island tend to get bigger, larger animals tend to get smaller. The reasons are not given in the book. If Noah's Ark did happen and seup on Mount Ararat, we should observe decreasing species diversity as we go away from the Mount. Gondwana was the old continent consisting of : South America, Africa, Antartica, Madagascar, India and Australia. tectonic plates are no pushed from behind by upwelling volcanic forces at the ocean ridges. Instead they are drags all along their length by the convective current under the surface of the plate. Earth's magnetic pole reverses at intervals of 10.000 to 100.000y (probably due to slowly oozing currents in the mixture of molten iron and nickel in the planet's core). This led to clearly visible patterns of the magnetism of the rocks formed on each side of an ocean ridge. Chapter 10 - The tree of cousinship The pterodactyl's wing membrane is supported by what would be for us the "little finger". A horse's hoof is homologous to the fingernail of our middle finger. The smaller lower bones of the rectilian jaw (we only have one lower bone for the jaw) became part of the mammalian ear to become a bridge that transport sound from the eardrum to the inner ear. A dolphin beats its tail up and down (and not left right like fishes), which come from the fact that it is a mammal and has an ancestror that was on land. On land, speed is often aquired by bending the spine up and down. On the opposite, lizards and snakes inherits from the fish behavior and move side to side. Snakes swim on lands, and dophins gallop through sea. Some bacteria seem to be able to borrow genetic information from other bacteria. In animals, unlike bacteria, gene transfer is almost entirely confined to sexual congress within species. (Side note: plants of the pea family (leguminosae), have nodules on their roots where some bacteria grow and capture nitrogene from the atmosphere and make it available to the plant. This is why farmers use leguminosae in their rotations: it brings nitrogen to the soil. The nodules have a red color because they contain a form of haemoglobn similar to the ones carying oxygen in our blood.) Vertebrates have hard bones inside a soft body, curstaceans have a hard exoskeleton inside which the animal keeps its soft bits. The closness of population was studied by Vincent Sarich and Allan Wilson in 1960 based on the immune response to a protein generated by another species. The closer you are to a species, the less yourr immune system responde to it. If you gradually heat DNA, there is a "melting point" around 85deg where the bound between the two helices breaks. The helices combines again upon cooling, but may not combine with the same one! Fragments of DNA will find other fragments with which they are compatible, even from another species. DNA is just DNA. Some bounds have higher strengths than others though. The strength of the bound can be determined by the value of the melting point. It is possible to see the closness of species by combining helices from different species and looking at the melting point. Hodkin's Law: Genetic technology is expanding exponentially (e.g. number of bases sequenced for a given price). Like Moore's law (Gordon Moore was one of the founder of the Intel computer chip): the number of units that can be packed into an integrated circuit of a given size doubles every eigtheen months or so. We estimate that there has been about 10 millions of surviving species. The molecular clock. Neutral genetic changes have no effect on the survival of an animal, and this can be used for a clock. Most mutations are actually neutral and can be detected by molecular geneticists. A lot of genetic material is useless (estimated at 95% in for humans). After a significant time, and at a predictable rate, neutral mutations are found everywhere in the gene pool (they have fixated). Chapter 11 - History written all over us Our hairs and goose bumps. Mammals with a lot of hair, when cold, it increases the layer of air between the skin and and the furr to keep warm. It's the opposite when too warm, the thinner the layer the easier the body heat escapes. For mammals it's also used to look more scary when they are threatened. Dolphin used to be a land animals. It doesn't have gills. It breathes trough a blowhole that has a tight-sealing valve. The human brains looks like a walnut because increasing the skull makes it harder for the baby to be born. Doing wrinkles is more efficient to increase the area of the sheet. Mammals features: wrinkled brain, placenta, milk, four-chambered heart, a lower jaw with a single bone, warm-blood, etc... Warm blood is convenient to optimize some chemical reactions. Mammals keep their body temperature constant (at an energy cost) to optimize this. So called cold-blooded animals can have blood temperature that fluctuates from values higher and lower than us (lezard). A bird that forgot he couldn't fly: kakapo, in New Zealand. Troglobite: animals that lives in the darkest places and there only (not the same as troglodyte) There are more chances that a mutations will make things worse. This is especially true for large mutations. Think of the body as a complex electronic system. Very small mutations will have a 50/50 chances. The eye is an example that doesn't make more sense: the photocells are pointing backward, so that the light has to go through the wires first. Also the wires have to go through the retina to reach the brain, hence our blind spot.. The gills from fish became thyroid glands and the larynx. The vagus nerve/ laryngeal nerve makes a crazy detour through the heart before coming back to the head. Because for the fish it made sense everything was next to each other. For the giraf, it's a crazy big detour. It's just easier and more likely for the evolution to increase the length progressively as the neck increases, instead of having a mutation that will do the jump. The testicules ended up descending (probably to be at a better temperature), but in their process, the vas deferens cable got hookes the wrong way over the ureter. Boyle's law: for a fixed quantity of gas at a give temperature, the pressure is inversly proportional to the volume. pV=nrT Fishes have a swim bladder, and the control the amont of gas in it by exchanging with their blood. More gas implies more volume and hence go higher up with Archimedes. Skarks have to do muscual work to stay up or down, not the fish. Koalas descen from some wombats that digging soil with their paws. There pouch for kids was open backwards to avoid the kids being full of dirt. But for Koalas it makes no sense. Our drainage hole for the sinus is well positioned for quadripeds since gravity helps them, but not for us standing up. Chapter 12 - Arms races and evolutionary theodicy Photosynthesis was invented more than a billion year ago by a free-living green bacteria. It somehow got hijacked into plant cells where they evolved into chloroplast. Another class of bacterias, mitochondria helpt converts sugar into energy. Both mitochandria and chloroplasts descended from different kind of bacterias that existed billions of years ago. If trees agreed as a group, they would not be that high. It's the balance of costs and benefits to the individual treees that finally determines the heights to which trees are pressed to grow, not the benefits that a rational planner could calculate for the trees as a group. Two hikers are pursued by a bear. One hiker runs away, the other stops and put on his running shoes. Are you mad? even with running shoes you can't outrun a grizzly! No, but I can outrun you! Natural selection doesn't step in (to step, be wise as a group otherwise you are going to go extint), doesnt look into the future and doesnt chose between rival groups. Prudent predation doesnt exist. Natural selection can drive population to extintion. Cruelty/Nature: Viruses and tigers are both build by coded instructions whose ultimate message is like a computer virus: "Duplicate me". Suffering is a by-product of evolution by natural selection. Pain is here to tell you don't do that again. But why does it have to be so painful. Ichneumon wasps paralyse but dont kill their victims (caterpillars), and lay eggs in them so that the larva have fesh meat. Even the larva eat the victims in a judicious order. Chapter 13 - There is grandeur in this view of life All living creatures on this planet are descended from a singel ancestor. The eveidence is that the genetic code is universal. It's a 64 words dictionary, using 4 letters (adenine, guanince, cytosine, thymine), made of 3-letter long DNA words, that are translated into 20 amino acids (some are duplicate) and one punctuation mark (start or stop reading here). Tidal cycles are important for marine and coastal organisms, and people have wondered if this could be linked to our monthly reproductive cycles. The universe is goind towards a heat death: the energy is being degredated from forms that are capable of doing work to forms that are incapable of doing work. All the free oxygen in the atmosphere is the product of life. Stanley Miller's experiment: a flask full of simple incredients, bubbled and sparked for a week before yielding amino acids and pre-announcer of life. The RNA-world theory. Proteins can't make copies of themselves. So proteins cannot be the key step for the origin of life. They coil up and hide their content. DNA doenst coil up, it keeps it's linear form which makes it a good candidate for a replicator. But DNA needs enzymes to catalyse its replication process. RNA theory says: RNAis a good enough enzyme to hold the fort until proteins evolved to take over the enzyme role and RNA was a good enough replicator to muddle along in the role until DNA evolved. Maybe there is no plausible theory of the origin of life, if life is so rare.