Wednesday, December 1, 2010

On Evolution: Quiet Accumulations

[Note: a good chunk of this text is from old stuff I'd written on this and at least two other attempts at science-oriented blogging. It's critical to note this post is an exercise to write for absolute beginners with zero knowledge of science.

Anyway, with little feedback (no one came, no one saw, no one, um... critiqued), I guess I kept giving up. However, I keep going back to these old bits and re-working them with new introductions, new frameworks, etc. So here it is again. I have a bunch of the other chunks that follow this which - I feel - make a complete story. Just need to work out the kinks. Now about that feedback...]

Before reading this,  
please read Part 1 to follow my train of thought.


The simple summary from Part 1 is this:
  • DNA is the instructions, written in a simple alphabet, that says how to build proteins.
  • Proteins are the things that actually go about building you.
  • You - and everyone else - start off life already having a bunch of changes, or mutations, in your DNA



You are the Boringest. Mutant. Ever!

"I was lead to believe that mutations do dramatic things, mostly bad"

Yes.  I understand that.
The key here is that you were led to believing this.
So this type of thought is understandable.
It's also wrong.

But that's not your fault.

Who's doing this "leading"?  Now, I could pin this on groups that deny evolution for purely religious reasons.  And yes, they are certainly doing their best to make everyone else believe the following:

  • Evolution needs "good" mutations to work.
  • Mutations are always bad:  They make deformed things!
See!
SEE!!!
  • Therefore, evolution doesn't exist.

Turns out, not too surprisingly, that all these points are wrong. 


But, you know, there's also another "leader" here.   And it's behind a similar belief - not that all mutations are harmful, but that:
all mutations DO SOMETHING REALLY BIIIIG!
And where would this idea come from?

Yes, you do know where:


Mutants
Mutants!

MUTANTS!!!

Uh... WOW!!

Yeah, that's where.

So, reconcile this:   just a while ago I spent a whole post yammering on about how each of us were born with mutations - a scattering of new changes within our DNA instructions.  If so, these changes in instructions should alter the way some proteins are made - and that should somehow affect us.

So why aren't there just legions of three-armed twenty-eyed people wandering the streets - or at least why the heck don't I look like Hugh Jackman?


The simple reason for this is:
Most new genetic mutations creep in silently, resulting in neither obvious harm nor help to the person who has received them. 
A brand new mutation which results in a something really unusual or disturbing, can happen.
But those dramatic mutations (er... the real ones, not the comic/TV ones) are far, far rarer than those that do... well, next to nothing.



There's Typos... and There's Real Frak-ups

First, I should address the things most people might expect a mutation to do: something significant. This can happen, but it's not as common.

If we again use the loose analogy of DNA as a book of instructions, and mutations being mistakes when copying the words of the book to a new one, then the error, or mutation, that happens most often is like a simple spelling error.


As an aside, there are more severe ways of messing up DNA:   Missing sentences, whole pages torn out, shoving bits of some other book smack in the middle of a perfectly good sentence, duplicating a page or a chapter, flipping a chunk of the book around, and so on.  As you would expect for an actual book, these editing mess-ups are far more likely to wreck the meaning of what was originally written.  These real muck-up mistakes - things that would have gotten a book binder fired - are, fortunately, far more rare.

The hundred or so mutations in DNA with which every child is born are primarily the basic spelling error.

Given that, let me just review the basic possibilities that you - as a new born child - might have 

The Bad
Whether it's a particularly unforgivable spelling error or missing chapter-sized chunk of DNA, some (a small amount) changes cause major problems right off the bat.

And "bad" mutations are like that kid from It's Alive! or Rosemary's Baby, right?

Yeesh! The It's Alive! crawling alligator-toothed killer baby created by a bad batch of contraceptive drugs?
No.
And Rosemary's Baby was the son of the devil.  Not the same thing.


No,  Most of these "bad" results we won't actually see in a living child: the problems caused are so damaging to basic functions of life and development that successful pregnancy - or subsequent birth - might never happen.

The things most people think of as "birth defects" - physical abnormalities that are noticeable right away - are usually the result of far more rare kinds of

And then there are the occasional mutations which mildly (compared to the previous) affect a particular function of life - maybe a little, maybe a lot.  How severe an effect it is will depend on how important the function is for the person in the world where he lives.


The Good
What about a good or useful mutation?
Maybe having more resistance to a disease? 
Or!  What about flying?  Lightning bolts?  Looking totally Wolverine bad-ass!?
Well... Maybe, no, no, and only if you spend hours a day at the gym.

The possibility of something instantly good emerging from a single mutation is also very small - smaller than the likelihood of messing something up.  Also, life can't make a new thing out of thin air - it can only be a result of a simple tweak of structure.  This limits the amount of newness a single mutation might bring.

There are a number of known simple changes - just a minor alteration of a normal human protein - that allow some people to avoid certain diseases, so it's possible a rare child may have gotten the same mutation made from scratch.

(I plan to talk about an example of this in some other post [link placeholder, to hold me to it])


On the other hand, I can't think of an existing human component that can be mildly finessed to suddenly produce shooting ice bolts - so I doubt we'll ever see the insane (but awesome) X-men style mutations erupt from humanity... ever.

And then there are the occasional mutations which mildly (compared to the previous) affect a particular function of life - maybe a little, maybe a lot.  How severe the effect is will depend on how important the function is for the person in the world where he lives.

Oh... notice how the last paragraph here and that in the previous section are identical?  That's intentional.  But I won't go into that any more in this post.

The Vast Majority of the Indifferent

Talk of something useful or something bad arising from a mutation is certainly more interesting than "it doesn't do anything".  However, the simple fact remains that most mutations with which any child is born result in no real difference between how a they would function with that mutation and how they would function without it. It is just a basic fact of the way DNA and proteins work.

The reason for this non-effect is that many mutations are "acceptable" spelling errors, as far as your body is concerned.

Some may be a word spelled differently but which means exactly the same thing.   For instance, color and colour. Others may involve a misspelling where meaning is changed, but it is ends up not causing much of a problem.  If instead of writing "the cat is sitting on my lap," I wrote "the dog is sitting on my lap", you'd think this might be a problem.  But if the point of the sentence was to show that a pet is on my lap, well then dog, cat, iguana, whatever... it's a pet. 

So, many mutations just squeak by and are then locked in... unnoticed, on the whole, by anyone. 


Quiet Accumulations

Now, I've just sat here and made noises about how most mutations don't do squat.

And any one of us only gets a couple hundred of these. Considering your DNA instruction set is made up of a few billion letters, this is an almost imperceptible amount of change.

But mutations are also supposed to be fuel to the whole process of evolution.   If most of these mutations do nothing, how can they empower the massive change over time, or "descent with modification" that is so readily and undeniably observed in the world?

It turns out that because most of these mutations, introduced one by one in the DNA instruction book, are often not even noticed, changes in the DNA instruction books of a species can creep into a population over time.

And over time, over many generations, it begins to add up.
Think about this:
  • You inherited a few hundred mutations from your parents.
  • You give a chunk of those plus a couple hundred more to each child you might have.
  • They give a bunch of their mutations, plus some of yours and some of your parents’ mutations to their children.
  • And those children (your grand kids), in turn, give a whole collection of mutations from your parents, you, your child, and themselves to your great grandchildren.
And it goes on.

And it has always gone on.

It has always been going on since before we were born and will continue to happen long after we’re gone.


Because of all this, the changes accumulate.  Usually unseen by anyone at all.

And each time a new generation emerges, it's an all new mix-and-match grab-bag of possibilities - fresh combinations of mutations, both old and new.

Again, many of these end up being no benefit and no harm.

But at some point, for one of many reasons, a mutation - be it a brand new one or a mix of older ones - will make a difference.

For one of your descendants, who knows how many generations away, this accumulation of mutations could ultimately lead to something very harmful.

Or, on the other hand, it could result in something that will save their life, their family's lives, and the lives of *their* descendants.


Or it just might make their eyes greener, which some fellow future person might like - or dislike - just a bit.


You really won’t know what the effect will be - or how it will affect that future human - until the day that it kicks in.


But that day (or century, or millennium) ends up being very important.

4 comments:

  1. I need to visit and critique more often :)

    DNA is the instructions, written in a simple alphabet, that says how to build proteins. [careful because lay people expect and alphabet to contain 26 letters, not 4, (at least in most western countries), so how ca you say the same thing while conveying the amazing fact there are only four letters in the alphabet? Can you brining in codons right away?]


    * Proteins are the things that actually go about building you. [Do they? Or are you made of proteins? Do all proteins go about making you or so some proteins "make" you and others "comprise" you? What about fats and fluids and ions and and and...be careful with technical points because you can derail very quickly]

    * You - and everyone else - start off life already having a bunch of changes, or mutations, in your DNA [It's only a mutation if it's in comparison to something. So, compared to you mom and dad and you and me, you have a bunch of mutations. But in isolation, you have a unique genetic code containing a mix of mom & dad's genes as well as a few independent changes introduced by random chance.]

    I say all of these things not to discourage (you have a good blog and good voice when you write). You say this your version/attempt at writing for a lay audience. So, I'm trying to remember some of the things my editors and mentors thrashed into me when i started doing that :)

    Turns out it's really hard to do, and not enough scientists appreciate that.

    ReplyDelete
  2. YAY! A comment!!

    Hey, thanks, Tideliar - I do appreciate the input - a LOT.

    Yes, it's VERY hard to take it back to Square 1. Especially when making your point to a newbie in one quick blog-shot.

    (I mean, I'm guessing that's the case... I have no clear idea, which is the problem. I'm trying to push some of these onto unsuspecting friends - all non-science - to get a better clue)

    All your points (which all center on problems of clarity vs. brevity/analogy) are well taken.

    I *did* give a bit more description of some of my analogies in the first evo-ish post.

    But, yeah, I'm always worried that I'm either speaking too little, too much, or too incorrectly.

    For instance, in the prior post and this one I intentionally became very generic about what proteins do and didn't even mention any other molecule. Since the story was about DNA at this moment, I worry that, fats, salts, methyl-, acetyl-, etc, groups - which are really, really important - would be losing the thread. But again, I'm learning, so...

    Not that all this hasn't been done 10k times by other better folk, but it's exercise for me, if no one else. Which is the point.

    Thanks again!

    ReplyDelete
  3. "Not that all this hasn't been done 10k times by other better folk, but it's exercise for me, if no one else. Which is the point."

    I guaran-fuckken-tee it will make you a better scientists, thnker and communicator n matte what you do. Learning to communicate effectively and efficiently to a range of audience induces a clarity of thought and prupose that will impact other aspects of your professional life.

    Like, foe sho man! innit!

    ReplyDelete
  4. Post-ironic epic spelling fail, not withstanding, obviously...

    ReplyDelete