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Life Ascending

The Great Inventions of Evolution

Nick Lane

Approx 200 mutations every generation. Since split off from chimps about 6 million years ago, each side has had time to diverge about 1%. In fact we share 98.6% of genes, because natural selection stops the unfavourable mutations being passed on.

Debate over what the ATCG codons actually did. There are 20 amino acids. The 4 letters could be combined in 64 different ways, so in theory could generate 64 different amino acids. Turns out there is a lot of redundancy. All the codons (the 3 letter sequences) have a use , three stipulating 'stop here' and the rest coding for an amino acid. Three amino acids are encoded by six different codons, others only by one or two.

Suggestion that this is a 'frozen accident' - any change to the coding would result in failure. The fact that all organisms have this single version of the code implies that life arose just once.

Oxygen is the key to planetary life, even though just a waste product of photosynthesis. It finally overwhelmed capacity of planet to swallow it all up. All the iron in the rocks, all the sulphur in the sea and all the methane in the air that can be oxidised, is. Then free oxygen pours into the air and the seas. When it accumulates in the atmosphere it forms ozone layer, shielding life from UV rays.

And oxygen provides the energy for multicellular life, and makes possible a long food chain. Adding electrons to CO2 produces sugars, the ultimate source of our foods.

Author discusses a suggestion made by a biochemist (as to how the 2 systems of photosynthesis could have hooked up together). "Like the best ideas in science, this hypothesis has a simplicity that cuts through layers of complexity to the quick. It may not be right, for not all the great ideas in science are. But even if it's wrong, it shows how things could have come to be the way they are, and, by suggesting experiments to test it, guide researchers in the right direction."

The Cambrian explosion is best known, but also the colonisation of land, the rise of flowering plants, spread of grasses and the diversification of mammals. Occur when genetic promise meets environmental opportunity.

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