13 juin 2006

DVD : Evolution

In this famous mini TV series in seven episodes, Nova explains the whole idea of evolution. Fascinating!

  1. Darwin's Dangerous Idea

Finches (pinsons) of the Galapagos. Darwin’s grandfather, Erasmus Darwin, formulated one of the first formal theories of evolution in his Zoonomia. Hummingbirds with beaks of various lengths to feed on specific flowers. The sun does not revolve around the Earth, so the nature does not revolve around Man. New strategy to fight AIDS: when it becomes drug-resistant, take the patient off drugs for a few months so the virus goes back to its drug-susceptible state. The eye evolved from light-sensitive patches of brain tissue in our ancestors, to a cup, then a cup with a diaphragm, then a cup with a lense formed by water caught between two transparent layers. Darwin asked “Is through your grandfather or through your grandmother that you claim descend from an ape?” when he published his book. DNA can now be compared letter by letter (nucleotides) between species: man and ape have very few spelling differences. Isaac Newton and Charles Darwin both interred in Westminster Abbey.

  1. Great Transformations

If the entire history of the Earth is called an hour, in the first 50 minutes there are mainly microbes. Animal life appears in the last 10 minutes. All of human history lasts a hundredth of a second. Bacillosaurus found in the Sahara has legs, descends from a 50 million year old kind of wolf that had an ear bone on its skull found only on today’s whales’ skeleton. Whales and dolphins swim the same way dogs run, by flexing their spine up and down, not from side to side like fishes and sharks. During the Devonian, fossilized tetrapod shoulder bone is found, 370 millions years old. These fishes first developed fingers, and then left water for solid ground afterwards. Such fingered tetrapod fossiles found in Greenland display an “arm” very similar to a human arm: one bone, then two bones, then the wrist, and finally fin rods. Cambrian explosion fossiles caught in a catastrophic underwater mudslide 570 million years ago, when a puzzling exponential growth in the number of species was taking place. This is the time when animals first appeared. Study of Drosophilia reveals that the underlying structure of their body segments is triggered by a universal set of genes (Ed Lewis’ Nobel prize in 1995). The “eye gene” of a mouse triggers the growth of a normal eye in the Drosophilia. Fighting the leafy spurge in Dakota using another invader: the flea beetle.

  1. Extinction

Perhaps six mass extinctions have already taken place in Earth’s history, including the one of dinosaurs 65 million years ago. After a short period, their extinction allowed small mammals to multiply and grow larger. Scientists setting automatic cameras to take pictures and count wild animals in Thailand’s rain forest and measure a possible decrease in the number of animals (specially predators). Snakes infest Hawaii and 9 species of native birds are driven to extinction.

  1. The Evolutionary Arms Race

Multidrug resistand tuberculosis spreading worldwide from a prison in Tomsk because of inappropriate use of poor quality antibiotics. One of the world’s most poisonous animals is a newt found in Oregon. Why has it evolved to produce so much toxin as to kill thousands of predators? Because of an evolutionary arms race with a specific snake which has developed resistance to its toxin. But the snake’s resistance come with a price: more resistant snakes are slower. Milder kinds of infectious diseases travel by air like the flu, because they need their host to be alive to spread; the most potent toxin-producing bacteria are spread by bad water supply, because they can do so even when their host is lying down or dead. New strategy to try to domesticate these harmful bacteria by improving water supply and driving the disease towards its less potent forms. 10% of caucasian Europeans carry a gene that protects them from HIV; this gene is absent in african and east-asian populations. Dating techniques suggest that this gene spread 700 years ago, as 1/3 of the european population was taken out by the bubonic plague. Leaf-cutting ants in Brazil’s rain forest in symbiosis with a fungus. The leaves contain toxic chemicals which are broken down by the fungus, allowing the ants to feed on the resulting proteins and sugars. The ant and the fungus are dependant on each other: the ant secretes a kind of wax containing the same kind of bacteria which produces half the antibiotics used in human medicine, which in turn protect the fungus from mold. Study conducted in Bavaria where asthma and allergies are rare show that children exposed to cattle in their early childhood might develop a stronger immune system.

  1. Why Sex

Species of lizard that has only females, having offspring carrying 100% of their genes (clones). What evolutionary pressure drove most living species towards sexual reproduction? “Red queen” theory: Alice in Wonderland racing with the red queen is surprised to see nothing moving when she is running as fast as she can. The queen’s answer: “That is the point, to stay in the same place you have to race as fast as you can”. In pools with both sexual and asexual fishes, the clones are more prone to parasites. But after a severe draught, the sexual species is decimated and loses its genetic variability, it becomes inbred. It then becomes the primary target of the parasite and the asexual species seems to be doing fine. Reintroducing diversity by carrying the sexual species from a pool to another “cures” the sexual species, and the parasite evolves back to targeting the asexual species. Environmental factors that put pressure on sexual behavior: relative importance of quality of parenting vs quality of genes influences choice of male by female, availability of food (chimpanzees and bonobos). Survival rate of offspring influences maternal vs paternal nurturing of offspring: in a species of bird in Panama, so many chicks are lost to crocodiles that females must lay many of them and males keep them warm and raise the chicks, so that females fight over mates and have taken on the usual male characteristics. When women are asked to rate the sex appeal of young men based only on their smell, they consistently rate higher the men whose immune genes are unlike their own. Behavioral evolution tries to explain why we have evolved brains that make certain things feel good and others feel bad. Beauty features in women such as full lips and short jaws are associated with high levels of oestrogens and low levels of testosterone, that is fertility. When women are ovulating and have a higher probability of getting pregnant, there is a shift of their preferences towards more masculine-looking males. Geoffrey Miller’s theory is that the human brain evolved to its present complexity, including culture, sense of humour, etc. in an effort to attract sexual partners.

  1. The Mind's Big Bang

In a 43,000 year old site in Turkey, the oldest perforated shell beads in the world are found. This marks the beginning of culture, through decorative artifacts. Neanderthal did not have such capacity. Did mutations in their brain allow modern humans to invent art, burial of the dead, better weapons? Chimpanzees share with us a very subtle ability to understand the meaning of an interaction between individual in terms of a threat or opportunity for us, and manipulate them to our own advantage. Human children develop the ability to think of what others are thinking between the age of 3 and 5, which chimps cannot do. This is called the “theory of mind”. At the same time, this allows humans to be much more sneaky than other species. A community of deaf mute children in Peru developed their own very elaborate sign language. What is language used for? Actual studies show that people spend two thirds of their total conversation time doing social gossip. The is useful to know what happens when we are not around, who needs or can offer a favor, in addition to transmitting technical know-how or engaging negociations (I will give you some of my meat if you give me some of your fruit). Evolution of memes and genes is moving along hand in hand: abortion and education have changed whose genes are going to be replicated. Internet…

  1. What About God

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