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DNA does more than code for proteins, but in terms of proteins, 3-letter DNA codons already provide for 64 possibilities, and there are only 20 amino acids.
by dnhz 8y ago
DNA does more than code for proteins, but in terms of proteins, 3-letter DNA codons already provide for 64 possibilities, and there are only 20 amino acids.
- antirez 8y agoSo you mean, it did not evolve differently for lack of need?
- dnhz 8y agoThis is hard to answer. Why are there 20 amino acids in proteins, someone might ask? Which came first? DNA, proteins, or was it RNA? Origins of life research tries to answer these questions, but I am not an expert of that field.
- iskander 8y agoThe most common belief is that RNA came first -- it has both the information-carrying capacity and enzymatic activity. As for why are there 20 encoded amino acids (+ selenocysteine and pyrrolysine)? I've read that codon similarities hint at an original more compact alphabet of two base codons (allowing for up to 15 distinct amino acids and a stop). I've also read that the "more recent" amino acids, like cysteine, are more readily oxidized and thus provided some advantage as atmospheric oxygen levels increased. But all of these are guesses about the world before LUCA, which is really lost to us.
- nabla9 8y agoGenetic evolution is path dependent. Starting point of evolution severely limits where evolution can go. In other words, evolution never does whole system redesign. It's all legacy code from the beginning with incremental optimization steps in response to selection pressure at the moment. Genes and amino acids are very close to the starting point, it's unlikely that they are optimal outside the starting environment. 4 amino acids was enough to get things going, inserting new amino asides later would require redesigning all the machinery starting from scratch. Evolution can't do that, but humans might be able to insert news stuff.
- cft 8y agoThat's assuming that life originated only once. If there were multiple independent origins of life, then why couldn't they have had different base pairs and compete with each other in the evolutionary manner?
- deleted 8y ago[deleted]
- anticensor 8y agoIncompatible signals causing destruction.
- samirm 8y agoThey could, but if they originated in the same environment then the likelihood of that goes way down.
- ascar 8y agoI always wondered about that incremental optimization. It makes sense in a lot of ways, but then there are cases there big leaps happen, which would require many steps at a severe disadvantage in between. E.g. the evolution of flight. Flying is a huge advantage, but evolving towards a body capable of flight without being able to fly, should require millions of years of disadvantages to get the flying advantage. But incrememtal optimization and survival of the fittest contradicts a very slow process over several disadvantaged steps.
- sliken 8y agoI disagree with the millions of years of disadvantages. Imagine if you wiped the world of all fish/mammals/birds. Then populated the planet with a large number of "average" size rats. Environmental niches filled by squirrels, mice, small dogs, foxes, coyotes, raccoons, hawks, eagles, and numerous others would be left wide open. Those rats would start evolving into any empty niches, that were close enough. Over time/generations the further niches would become available. Smaller rats would take advantage of food sources that the mice used to eat. Better climbers would evolve to take advantages of what squirrels used to eat. Rats that specialize in eating insects would start to specialize. Some rats would even start to specialize in eating other rats. Other rats would specialize in not getting eaten and fill the niche left by rabbits. The rats that evolved into squirrel like mammals might specialize in jumping ever further to avoid the ground where the rat-dogs roam looking for rat-squirrels to eat. Said jumping might even evolve into flying squirrel like rats. Given enough time active flight would evolve. Rats would even start to populate the oceans.. much like whales did. Evolving into a bird requires efficient lungs, light weight (things like hollow bones), and not wasting weight on things like powerful legs, thick skin, etc. But every step of the way would be better for some niches.
- deleted 8y ago[deleted]