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Is this all that surprising? If mammals tend to have genome sizes of around 1-10 pg, and a mutation has a chance of around 10^-8 per base, then you would expect
by Jach 9y ago
Is this all that surprising? If mammals tend to have genome sizes of around 1-10 pg, and a mutation has a chance of around 10^-8 per base, then you would expect around 10-100 mutations per generation. So if you were sampling random members of a species at close periods in time, you would probably see a lot of genetic variation, but over wider stretches of time, the later samples are only descendants of the old genes that reached fixation and survived, plus whatever new mutations centered around the later time. Fixation is slow and depends on the mutation's positive selection benefits and the overall population count, but some mutations happen every generation and most aren't positive... With viruses their mutation chance is even higher... This is just from references in the 90s, so is Ho's result just a nice math model to better take into account time scales with samples?
- Retric 9y agoI think the issue is local optima. The Cambrian explosion is known for a huge diversity of forms, but diversity generally means a lot of sub optimal results which mostly get killed off. Beyond that, what worked for trilobites largely works for horseshoe crabs. Consider if something is getting larger by say 1% per thousand years, well over 1 million years that's simply unsustainable without becoming ~21,000x as large and thus a very different organism. Further conditions may change promoting periods of shrinking which means the average is going to trend to ever smaller changes per period of time.
- veddox 9y agoI'm sorry, I really can't follow your line of reasoning here. Could you elucidate?
- Retric 9y agoSure, a fox is not the size of a wolf because both are useful sizes to be. If you follow the evolution of foxes getting slightly larger or slightly smaller both provide advantages so it's really a balance which may change over time that determines what happens. AKA, fox sizes might drift up and down some over time, the average is going to stay near their current size unless say wolves died out. At which point they may quickly get larger and replace wolves, but they would not keep growing indefinitely and end up the size of great whales as they are now constrained by the 'wolf' niche. Further, foxes may end up spiting, you have foxes that look about the same, and foxes that look a lot like wolves. Now if you chart sizes as say 10,11,12,11,10,9 then the transition between those stages is a 'fast' + or - 1, but the net result is only -1 over 6 steps or -1/6th. The same thing is likely going on with less obvious features, but they are less intuitive.
- daxfohl 9y agoAgreed, I was surprised this was surprising. I saw some study where some moths can evolve from white to black in a couple generations if they go from white bark forests to black bark forests. But that doesn't mean they'll evolve into something unrecognizable in a hundred generations. I was just looking at Taylor expansions today (guid uniqueness...birthday problem), so, this kind of reminds me of that. First you evolve, then you evolve the ability to evolve, then you evolve the ability to evolve the ability to evolve, etc. So maybe there's a formula.