On Human Evolution

[mystictiger]

As a spin-off from the Evolution-Religion thread somewhere on this subforum, I was struck by a comment made by Jude as to evidence of continuing human evolution. When I was going through medical school, the prevailing view was that medicine and technology have stopped evolution. I don't believe that this can be true as medical technology doesn't make someone more attractive, merely less dead.

What macro-evolution is taking place? Do we all benefit from it? What would it look like? At what point do we step in transhumanism and speciation?

I'm aware that this is a vague and general topic and string of questions, but I'm fed up with the inevitable sci-fi cliche of psioncs, or changing into beings made of thought / energy / cheese. I would welcome your comments, thoughts, and links.

[Trieste]

>.>

<.<

http://www.indigochild.com/

*runs away*

[mystictiger]

A higher state of evolution?!

*froths at the mouth*

That's ... that's... so hillariously bad.

[Oniya]

I'm not sure that 'Indigo Children' are a genetic occurrence.  The descriptions all strike me as a psychological difference (I'm not going to say disorder, because there's not really a lot that looks inherently bad about it, other than a possibly higher incidence of oppositional defiance disorder), rather than something that could be selected for/against.  The one aspect that could move them to an 'evolution' is the fact that they 'seem antisocial unless they are with their own kind. If there are no others of like consciousness around them, they often turn inward, feeling like no other human understands them. '  This could lead to a greater likelihood of 'Indigo Children' forming relationships with other 'Indigo Children', with a resulting population genetics shift.  (EDIT - this could result in something similar to 'Founder's Syndrome', which is a higher incidence of recessive conditions in a population arising from a limited initial sub-population).

As for the initial premise - that medicine and technology have limited evolution - the one thing that I can say in regards to this is that many inheritable diseases that used to be fatal can now be treated with drugs/surgery/etc.  As a result, those people carrying those genes make it into the reproducing population, and the genes get passed on.  As a result, bad genes are not being naturally selected against - unless people carrying those genes make a personal decision not to pass them on.

Fun fact:  Sickle-cell anemia, while debilitating in the homozygous expression, is actually an effective counter to malaria in the heterozygous expression.  That's the sort of condition that only an environmental change (the elimination of malaria) could hope to start eliminating, because both the homozygous dominant (normal cells) and the homozygous recessive (sickle cell anemia) would result in higher death rates in a malaria-ridden area.  The dominant, because they would have no protection, and the recessive because of the deformed blood cells getting stuck in capillaries.

This doesn't mean that good genes aren't selected for.  Attractiveness is a complicated thing to measure genetically, but 'healthy' tends to 'look better' than 'unhealthy'.

[Hunter]

http://www.indigochild.com/

Guilty.

[Trieste]

Of...?

[mystictiger]

Of doubting the existence of we indigo children!

*shuns the boringly aura-ed one*

[Salamander]

Biological evolution is glacially slow when compared to social and technological evolution. That doesn't mean that human biological evolution has stopped- in fact it can't stop. One commonly held definition of evolution is a change in the gene frequencies within an inter-breeding population over time, and of course gene frequencies in a population must change over time. Even if there are no significant natural-selective pressures, there will still be neutral drift. However, I'm inclined to think that the huge gap between the pace of biological evolution and that of social and technological change means that biological evolution isn't very important to humans any more. And in fact hasn't been important for some millenia- since the advent of agriculture perhaps.

I suppose that I'm a transhumanist of sorts. My own thinking has been heavily influenced by the philosopher Andy Clark, whose writings I would strongly recommend to anyone with an interest in this kinda thing. The book Natural Born Cyborgs is especially good. Some of his papers are on-line here. The stuff on the extended mind is particularly relevant.

And thanks to Trieste for the Indigo Children link. Absolutely hilarious.  :D

[Trieste]

Of doubting the existence of we indigo children!

*shuns the boringly aura-ed one*

There.is.no.such.thing.as.Indigo.Children! *rages*

[DarklingAlice]

It is actually impressive the number of genetic mutations that get selected for to deal with certain environmental threats in human populations.

As Oniya mentioned, sickle cell (and indeed alpha & beta thal, and certain red blood cell membrane disorders) provides resistance to malaria. And since sickle cell or thal trait (heterozygosity) isn't lethal (and most of the disorders are less lethal than malaria) they continue to get passed around populations with increasing frequency.

Similarly CCR5delta32 mutation provides immunity to HIV (and the acquisition of the mutation through HSC transplant in fact cures HIV) and is posited to have afforded immunity to the bubonic plague as well (its frequency in populations of European descent has allowed for a putative model for its selection). These are only two of an increasingly large library of what are essentially human resistant strain mutations. Of course, as with all mutations, these tend to have cascade effects and unpredictable consequences.

Medicine doesn't pose any risk of stopping evolution, rather it alters the selection criteria. Evolution won't stop without something radically shifting in polymerase mechanics and nucleic acid chemistry. The question is how much natural selection we choose to allow, and how much artificial selection (and that is only within the boundaries of our ability to influence natural selection, which, while potent, are still in their infancy).

ImgSource: Ahuja & He 2010

[mystictiger]

I have no doubt that there are small scale local adaptions to various environmental conditions - sickle cell, ApoE mutation, and so on. I was thinking more of the large scale macro-level changes that might lead to speciation. The kind of thing that would be to us as we are to various proto-humans.

Am I conceptualising this incorrectly?

As to the stopping evolution, I was under the impression that mutation -and- selection were required. Thus it would take more than change in the way mitosis and meiosis occur.

[DarklingAlice]

I'll deal with the easier answer first, if you don't mind:

As to the stopping evolution, I was under the impression that mutation -and- selection were required. Thus it would take more than change in the way mitosis and meiosis occur.

Yes. It takes both. But mutation is primary. If there is no mechanism of variation, we just have static alleles. So yes, one phenotype would still be selected for, but you would have a finite number of phenotypes because of a finite number of genotypes.

This is primary to mitosis and meiosis. We mutate because A) nucleic acid chains have only so much stability, which is how we get 'induced' mutations; B) the processes of replication and transcription have a certain basal inaccuracy (~10^-6 to 10^-9 depending on the type of creature and which polymerases are used) which gives us 'spontaneous' mutations. Further variation is induced through recombination, also dependent on the biochemical properties of DNA. Some organisms are also lucky enough to be able to use plasmids, conjugation, transformation, and transduction, not us though (although we are working towards transduction with viral gene therapy).

Once this variation occurs two things happen 1) certain changes are selected against (if for no other reason than that any mutation tends to lower survivability regardless of its benefit); 2) certain changes are selected for (and if this selection overcomes their cost, then they stick around). Now, not all selection is natural selection. In fact, the first chapter of the Origin of Species is about artificial selection (the mechanism by which we converted wolves to dogs and a undifferentiated cabbage-like ancestor to like 7 different types of edible plant). There is also sexual selection, where one sex determines a sexually desirable feature regardless of its survival benefit (e.g. if overnight all men started only wanting redheads).

So in essence, mutation (and recombination, etc) provides the mechanism, selection (regardless of type) provides the direction.

I have no doubt that there are small scale local adaptions to various environmental conditions - sickle cell, ApoE mutation, and so on. I was thinking more of the large scale macro-level changes that might lead to speciation. The kind of thing that would be to us as we are to various proto-humans.

Am I conceptualising this incorrectly?

A little. Macro-level changes do not occur in leaps (with incredibly rare exception). This is for several reasons: 1) Genes aren't all they are cracked up to be. This is why I often talk of the "failed promise of genomics". There isn't an X gene (damn you Marvel comics!!!). No one gene works completely alone and the vast majority work in headache inducingly complex networks, one of the features of which is redundancy (this is why we can generally only say you have a pre-disposition to cancer, because it generally takes 3 specific separate gene mutations to get a single benign tumor and 5 for malignancy); 2) Unlike bacteria, we have large non-coding regions and mutations that fall there tend to be silent; 3) only genes in our gametogenic (is that a word ?_?) cells pass on. This is why gene therapies aren't hereditary. So of all the cells in your body, only certain baseline stuff tends to matter for your offspring. Again, this is why if one of your parents was pre-disposed to cancer and indeed contracted cancer, you would still be only pre-disposed and have a chance not to contract cancer.

All of these mechanisms work to ensure that grandiose changes don't happen. And for a very good reason, this is what makes macroscopic life possible. We don't have the luxury of being able to have half of our body die off to select for the  resistant bits and let them regenerate into a whole (like say a bacteria colony would). No one gene can make or break us, not even those which we generally think of as causing single gene disorders (like sickle cell, active HbF provides a suppressor mutation). I posted about this a while back when I made reference to the wonderful paper: "Human disease classification in the postgenomic era: A complex systems approach to human pathobiology." Loscalzo, et al. 2007.

The end result is that mutation at the animal level is much less dynamic than under the microscope; and this goes double when you are dealing with humans who are one of the most extreme K-selectors.

I tend to dislike Dawkins (more for his attitude than his actual views), but he does have something relevant to say here:

"Take a rabbit, any female rabbit (arbitrarily stick to females for convenience: it makes no difference to the argument). Place her mother next to her. Now place the grandmother next to the mother and so on back in time, back, back, back through the megayears, a seemingly endless line of female rabbits, each one sandwiched between her daughter and her mother. We walk along the line of rabbits, backwards in time, examining them carefully like an inspecting general. As we pace the line, we'll eventually notice that the ancient rabbits we are passing are just a little different from the modern rabbits we are used to. But the rate of change will be so slow that we shan't notice the trend from generation to generation, just as we can't see the motion of the hour hand on our watches - and just as we can't see a child growing, we can only see later that she has become a teenager, and later still an adult. An additional reason why we don't notice the change in rabbits from one generation to another is that, in any one century, the variation within the current population will normally be greater than the variation between mothers and daughters. So if we try to discern the movement of the 'hour hand' by comparing mothers with daughters, or  indeed grandmothers with granddaughters, such slight differences as we may see will be swamped by the differences among the rabbits' friends and relations gamboling in the meadows round about."
-The Greatest Show on Earth Dawkins, 2009