

Evolution: A Complexity View - namlede
http://rjlipton.wordpress.com/2014/09/22/evolution-a-complexity-view/

======
tjradcliffe
While it's true "the role of sex is not completely understood" in evolution,
most current research points to co-evolving parasites as a major force that
makes sex a good evolutionary move. It increases inter-generational variation
while at the same time preserving viability (because both parent organisms are
viable) which merely adding randomness would not do. Parasites are typically
incredibly specialized because the hosts always evolve pretty good first-line
defenses, so the additional genetic variability that sex produces from
generation to generation becomes a considerable added benefit to the host,
because the parasite population is always playing catch-up. Like many things
in evolution, the war is never won, but sex tips the strategic balance in
favour of the host.

That said, this kind of formal, mathematical approach to evolution is becoming
increasingly powerful, and it's worth speculating if there might not be a
provable theorem connecting random DNA variation and the laws of probability
at the molecular level with the fact of macroscopic evolutionary change,
speciation, etc... something like Boltzmann's H-theorem in thermodynamics,
which attempts to show how micro-physics (kinetic theory) can be used to prove
the macroscopic 2nd Law of Thermodynamics.

This would make evolution not a theory but a theorem, which I call "Darwin's
Theorem". I've played around with the math a bit (I'm a physicist, not a
mathematician) without getting anywhere, and wrote a what-if novel about the
possibility (it plays with even more speculative ideas as well), in part with
the thought of popularizing the idea, because I think it's worth people
thinking about: [http://www.amazon.com/Darwins-Theorem-TJ-Radcliffe-
ebook/dp/...](http://www.amazon.com/Darwins-Theorem-TJ-Radcliffe-
ebook/dp/B00KBH5O8K/ref=sr_1_1?ie=UTF8&qid=1411573921&sr=8-1&keywords=darwin%27s+theorem)

~~~
schrodingersCat
While the fact that cross-over during meiosis does in fact contribute to
increased genetic diversity leading to resistance to disease, parasites, and
other adaptational advantages, one still needs to answer why did sexual
reproduction evolve at all? Bacteria and protists are quite good at promoting
genetic diversity through horizontal gene transfer, and viral infection with
natural DNA replication error rates provide enough sources of "random" genetic
variation to keep a diverse gene pool. One can think of competition to share
genetic material as a primordial form of sexual selection. Getting from this
kind of competition to orchestrated sharing and cross over of large genomes is
a huge jump. The real question may be, did increasing organismal complexity
necessitate a different type of reproduction to maintain genetic diversity?
The answer to this may be yes, but alternative, less sexy hypotheses have to
be tested as well. Another question to answer would be – What evolved first:
multicellularity or sexual reproduction?

~~~
vegggdor
> enough sources of "random" genetic variation

well, that's the kind of thing the GP wants to put in numbers and a
mathematical system, to provide substantial arguments.

------
schrodingersCat
This paper makes a 0th order assumption that there _is_ an inherent advantage
to sexual vs asexual reproduction. There are certainly advantages to both, but
the author is correct that the answer may come out of addressing complexity.
Algorithmically, there are many approaches to modelling sexual selection
(rather than natural selection). Sexual selection occurs much faster than
natural selection and may be one of the reasons why we have such apparent
gender differences within species. Describing the effect of complexity in
terms of "fitness" is one of the largest challenges faced by computer
scientists and biologists this century. If you are interested in exploring
some different algorithmic models, "Computational Molecular Evolution" is an
excellent book ([http://www.amazon.com/Computational-Molecular-Evolution-
Oxfo...](http://www.amazon.com/Computational-Molecular-Evolution-Oxford-
Ecology/dp/0198567022)).

~~~
arketyp
I'm confused by your distinction between natural selection and sexual
selection. I always thought the latter was encompassed by the former. Are you
talking about random phenomena like genetic drift, or that some complexities
are not susceptible to adaptation? Did only browse the article, sorry.

~~~
schrodingersCat
Its generally understood that traits that encourage reproduction _regardless
of whether or not they encourage fitness_ will outperform other traits
([https://en.wikipedia.org/wiki/Sexual_selection](https://en.wikipedia.org/wiki/Sexual_selection)).
This is why you will see the appearance of coloration and seemingly useless
adaptations faster than actually beneficial traits within a population (i.e. a
giraffe's neck; its not for reaching those high leaves). Natural selection is
generally concerning traits that promote survivability over time, a much
slower process. A major hypothesis is that sexual selection may be a driving
force behind differentiation of the sexes, probably originating from genetic
information sharing among single-celled organisms. A competing hypothesis is
that there is an _intrinsic_ advantage to sexual reproduction versus asexual
reproduction. I generally favor the former hypothesis because it generally
fits the "short-sightedness" principle of evolution.

~~~
arketyp
I agree with you. I wrote an essay once about the need to be sentient about
what characteristics of biological evolution one adopts in genetic
programming, arguing that sex is arguably just a serendipitous side-effect or
at least a sub-optimal solution to the problem of effectively mixing gene
material. Much points to this, such as the short-sightedness principle of
evolution, and that group or species selection argument is generally hard to
make.

However, I am still reluctant to accept your distinction between natural
selection and sexual selection. The article you link to even calls sexual
selection "a mode of natural selection". The giraffe neck does not have
fitness value in the sense of making it a better food processor, quite the
opposite. But it does have fitness value in the sense of prospering those very
genes, indeed otherwise the giraffe would not exist. Such a definition of
fitness does tend to be tautological, but the alternative is no better,
because it is inevitably based on a measure of survivability that in the end
is necessarily arbitrary.

~~~
PeterWhittaker
The basic distinction is this: Natural selection refers to one organism having
superior reproduction prospects due to inherent physical factors (strength,
speed, height, weight, ability to digest specific foods, ability to detect and
respond appropriately to threats, etc.). Natural selection takes place without
the awareness of the hosts involved: By the time their relative advantages or
disadvantages are in evidence, they are long dead.

In other words, natural selection is about fit, that is, how well an organism
"fits" or is suited to and environment. (That it what Darwin meant by fitness:
Environmental suitability.)

Sexual selection refers to overt preferences in mating: A female bower bird
chooses the male that builds the "best" bower (a completely useless artifice
neither ever use), a human male prefers women with larger breasts (pretty much
ditto), a peahen prefers the peacock with the more extravagant tail (ditto for
sure, in fact, more extravagant tails are liabilities).

Examples are many. The term "runaway sexual selection" is used to refer to
exaggerated traits that become prevalent and possibly dominant in specific,
local populations (think of human characteristics you associate with certain
groups: Sometime, somewhere, someone preferred those slightly larger eyes or
slightly curvier hips and over time those became prevalent). These traits are
generally completely irrelevant, with zero fitness value.

They exist because we think they look/smell good. Why did we come to prefer
one over another? The same random variation that causes changes to fitness
causes changes to fitness indicators, but those indicators are not necessarily
honest signals.

~~~
arketyp
I am familiar with the gene-centered view of evolution proposed by Williams
and popularized by Dawkins with the so-called selfish gene theory. Within this
school of thought sexual selection by no means stands in contrast to natural
selection and is not labeled an alternative to it. Instead, in fact, sexual
selection is argued to be a direct consequence of natural selection as a
phenomena you would expect with Darwinisitic reasoning when assuming the gene-
centered view. As is made the case, the gene-centered view is the extension of
Darwin's original argument, that is, Darwin's argument taken to its logical
conclusion with the modern facts at hand, the DNA molecule not the least.

One of the central themes in Dawkins's The Extended Phenotype is the putting
into question of the validity of traditional role of the organism in
Darwinistic reasoning and why Darwin's original definition of fitness does not
hold up. There is actually an entire segment on the many modern (back then)
definitions of fitness and problems with each of them. I don't recall what the
final conclusion is but it is certain it is not the clear-cut case you make
it.

I suppose you have background in a field where your definition of fitness is
more firmly established. For instance, I know biological mathematics has come
a long way, and I'm not up to speed with what definitions they are using.

------
j2kun
There is an algorithmic technique underlying a lot of this stuff called the
"Multiplicative Weights Update Algorithm." It's worth checking out if you want
a cool algorithm that applies in lots of different scenarios.

------
chriswarbo
This reminds me of Chaitin's "meta-biology", which uses (self-delimiting)
computer programs as genomes, a Turing machine as the environment and
"fitness" is defined as how big the program's output is, interpreted as a
natural number. Unfortunately it relies on a halting oracle to avoid diverging
programs :(

~~~
otoburb
Here's a copy of Chaitin's metabiology draft notes compiled from a series of
lectures he's given over the years:
[https://www.cs.auckland.ac.nz/~chaitin/metabiology.pdf](https://www.cs.auckland.ac.nz/~chaitin/metabiology.pdf)

