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The theory of evolution states that random variations in organisms occur to better suit their surroundings. We take for example a bacteria's flagella. There's a bacteria who has a tube kind of structure that it uses to inject toxins in other cells. Structure of flagella and this tubular structure is very similar. So biologists state that this is clear evidence for evolutionary process wherein this tubular structure underwent gradual changes that resulted into a flagella.

Now my question is, minute changes did occur to this tubular structure, but how do those changes get carried over to the next generation? Almost all components of a cell are created as per the instructions coded into DNA. So does it mean that every minute changes that occur to an organism get recorded into DNA so that they can be carried over? In above example, assume, that a few proteins got accidentally attached to the tubular structure that will help the structure to rotate. Now when this temporarily changed bacteria gets divided into a new one it will have lost that change. So to actually carry over this "beneficial" change would the bacteria have changed its genome? How does this happen? What is the basal mechanism that supports evolutionary changes?

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    $\begingroup$ Changes to the organism don't get recorded in the DNA, changes on the DNA generate differences in the organism $\endgroup$
    – rg255
    Apr 28, 2015 at 9:53

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As populations expand, generation by generation, they will inevitably run into limits on resources. Not all individuals in a population are exactly alike as some will have traits that give them an advantage in survival. A change in any aspect of the environment can suddenly turn what had been just another variation or variant into either an advantage or a disadvantage If a selective pressure (i.e. change in the environment), acts against or upon the differences between the individuals in a population, you get natural selection, which, through time, can cause a population to evolve

http://rmitchellbioanthro.weebly.com/uploads/2/3/7/6/23767919/natselinanutshell.pdf

Evolution consists of two essential things:

Random mutagenesis (in this case a slight change that occurs in the DNA, that causes a slight change in the protein to show up)

The second stage of evolution is natural selection. After the mutagenesis event, nature rigorously selects for the mutation. If the mutation has a fitness cost to the organism, it gets removed (the organism doesn't survive). By removing all things that are more costly than beneficial, nature selects for the fittest.

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Take the examples of beetels here (http://evolution.berkeley.edu/evolibrary/article/evo_25)

Very rarely does the external environment directly change the DNA code (you can argue about epigenetics, but that's a different can of worms). Changes in the environment usually dictate the survival of organisms with different traits. In fact what usually happens is a change in the DNA code occurs naturally due to mutagenesis and that change undergoes the rigours of natural selection.

So in you case what might have happened is (I am postulating here, I would recommend a literature search to verify this), your bacteria had a tubular structure that it used to inject toxins in other cells. Some bacteria (due to genetic variation in sexual reproduction) had mutations that allowed it to move this tubular structure. This allowed it to survive more efficiently, and hence reproduce more. Eventually this population of bacteria, slowly replaced the bacteria who had no locomotor control on their "tube", and hence one stage of natural selection has occurred. Now this happens again and again, till the efficiency of the locomotion is optimal.

Might I suggest you read this book ?

Bonner, John Tyler. The evolution of complexity by means of natural selection. Princeton University Press, 1988.

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  • $\begingroup$ So a fully functional protein can form out of random mutation? Or does that too evolve? Can you give me any links of evidence? $\endgroup$
    – Shades88
    Apr 28, 2015 at 10:12
  • $\begingroup$ Usually it's due to SNPs and INDELs that you get new versions of proteins. But again, that's rare where a new protein rises out of nothing. It's a very iterative process, and usually the proteins that make the cut are well conserved from then on. Usually, due to genome duplication events, one gene may code for the protein and the copy will not be under the same selection pressure, allowing it to accumulate mutations and experiment. Was I able to answer what you were asking? $\endgroup$
    – Rover Eye
    Apr 28, 2015 at 10:46
  • $\begingroup$ I'm not a biologist, just have a lot of curiosity in how molecular machinery in cells work. So I have no idea what SNP and INDEL is. Could u tell me the full-form? And I read somewhere that malfunctioning or wrongly folded protein does a lot of harm to cells so will randomly and then successively forming proteins cause problems? $\endgroup$
    – Shades88
    Apr 29, 2015 at 6:39
  • $\begingroup$ @Shades88 Basically they are small changes in the DNA code. Single Nucleotide Polymorphisms and Insertions Deletions. Anything that causes harm to a cell will cause cell death, and thats the end of that story. $\endgroup$
    – Rover Eye
    Apr 29, 2015 at 23:16
  • $\begingroup$ The two other forces of evolution are drift and meiotic drive. Michael Lynch fairly convincingly argues that complexity rarely if at all originates from natural selection. $\endgroup$
    – Jonas
    May 28, 2015 at 14:03

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