Evolution of complex organs

Well, I guess here is my best place to ask. How exactly does a species grow something as complex as the brain? I have always wondered this. I have looked in books, but they say that 'it did', rather than 'here's how'. I looked for online examples, and Ebon Musings says, talking about the brain and the soul, that the "fires of evolution have been working for 4 million years to cook up the brain the way it is," but if life only follows chemical reactions, random ones at that, how does such a thing arise?

You know, the obvious answer is that it has to. Even the SIMPLEST organism can't seem to survive without a concentration of the nerves into a single point of processing. So... if there are 100 billion possible ways for a 20 or 30 celled organism to exist, and 100 of them work BEST because of coordination between sensory input and rudimetary decision making... then after trillions of them only those 100 will flourish.

You can't think of it in tems of single organisms 'evolving'... think of it as huge numbers of organisms producing slightly different offspring. The subset of the population that is slightly better at survival will slightly direct future generations of the organisms in that direction. For the INDIVIDUAL, it's random. For the POPULATION it's group selection of the more survival oriented mutations.

Evolution is accumulative. For a good example of the evolution of a complex organ of which there is much information - look into the evolution of the eye.

http://www.don-lindsay-archive.org/creation/eye.html

The process has been replicated with computer simulations:

In an article in the May 8 issue of the international journal Nature, Richard Lenski, Charles Ofria, Robert Pennock, and Christoph Adami report that the path to complex organisms is paved with a long series of simple functions, each unremarkable if viewed in isolation. "This project addresses a fundamental criticism of the theory of evolution, how complex functions arise from mutation and natural selection," said Sam Scheiner, program director in the division of environmental biology at the National Science Foundation (NSF), which funded the research through its Biocomplexity in the Environment initiative. "These simulations will help direct research on living systems and will provide understanding of the origins of biocomplexity."

Source - http://www.nsf.gov/od/lpa/news/03/pr0351.htm

Here's the abstract to that paper:

A long-standing challenge to evolutionary theory has been whether it can explain the origin of complex organismai features. We examined this issue using digital organisms—computer programs that self-replicate, mutate, compete and evolve. Populations of digital organisms often evolved the ability to perform complex logic functions requiring the coordinated execution of many genomic instructions. Complex functions evolved by building on simpler functions that had evolved earlier, provided that these were also selectively favoured. However, no particular intermediate stage was essential for evolving complex functions. The first
genotypes able to perform complex functions differed from their non-performing parents by only one or two mutations, but differed from the ancestor by many mutations that were also crucial to the new functions. In some cases, mutations that were deleterious when they appeared served as stepping-stones in the evolution of complex features. These findings show how complex functions
can originate by random mutation and natural selection.

Source - Lenski, R., Ofria, C., Pennock, R., and Adami, C. (2003). The evolutionary origin of complex features. Nature, 423: 139-144.

One of the major arguments of ID proponents is that of irreducible complexity. By that they mean that some items are complex to have evolve like our brains, the eye, bacterial flaggelum, blood clotting and so forth. The major flag carrier of this idea is Michael Behe, a biochemist from Lehigh University. Sorry for Mr. Behe but he is wrong.

The situation with Behe also shows how ideology can overshadow even advanced education.

[a different tim]

Exaptation is important in the evolution of complex organs. Stephen Jay Gould's essay on the subject is here http://www.stephenjaygould.org/libra...onalshift.html
It's very readable and pretty much on the button on this topic.

An example is the bacterial flagellum the IDiots keep mentioning - the "irreducibly complex" flagellar rotor seems to be very similar to a simpler structure (a pore) that other bacteria use to excrete toxins.

a different tim wrote

Exaptation is important in the evolution of complex organs. Stephen Jay Gould's essay on the subject is here http://www.stephenjaygould.org/libra...onalshift.html
It's very readable and pretty much on the button on this topic.

An example is the bacterial flagellum the IDiots keep mentioning - the "irreducibly complex" flagellar rotor seems to be very similar to a simpler structure (a pore) that other bacteria use to excrete toxins.

Very interesting article! As a side note, the researchers discovered that beyond some length, the wings provided no more themodynamic advantage, proving some thermodynamics in the process. The maximum length is the same principle used when designing a cooling fin. The tip is at ambient, and the root is the body temperature. So the benefit then, for the longer wing, is for flight. (But the thermal advantages are not lost).

[Gnosital]

brad89 wrote

Well, I guess here is my best place to ask. How exactly does a species grow something as complex as the brain? I have always wondered this. I have looked in books, but they say that 'it did', rather than 'here's how'. I looked for online examples, and Ebon Musings says, talking about the brain and the soul, that the "fires of evolution have been working for 4 million years to cook up the brain the way it is," but if life only follows chemical reactions, random ones at that, how does such a thing arise?

While my input is not so technically elegant as that posted previously, a brain is a lot easier to explain than a wing, I think. It helped me get a grip on the possible sequence of events in the origin (genesis?) of brains by looking at the taxonomic hierarchy as a model of the evolutionary sequence. You can easily see a logical evolutionary progression from life forms such as bacteria (Monera kingdom) to true single celled organisms (Protista kingdom), to multicelled animals (Animalia kingdom). In animals, the cells differentiated to muscles and neurons. Among the simplest of the 15 animal phyla are those with a simple nerve net, like sea anemones and jelly fish. The nerve net (no brain and no spinal cord, just a reticulum of neurons) somewhat resembles the peripheral nervous system of humans, in that it consists of neurons that respond to environmental stimuli, but it also connects directly to other neurons that move muscles. Simple in-out messaging.

The next higher phyla include animals with more complex systems, including a specialized head, body and tail. The body in these phyla consists of a bilaterally symmetrical segmented nerve trunk. The segments are similarly organized body parts, each segment containing both a sensory input and a motor output. The human nervous system is also bilaterally symmetrical as well as segmentally organized (the dermatomes resemble flatworm trunk segments).

(Note that sacral segment S2 serves both the anus and the genitals... oh wait, that was another thread...)
(this one's the flatworm)

The next most complex set of phyla up the list, including clams, snails, squids (except for the far more highly evolved Solidsquid, of course), insects, and octopuses, have ganglia. Ganglia are small clusters of similarly functioning nerve cells that act like simple little brains. Humans have ‘em, clusters of them line the outside of the spinal column, they’re called the dorsal root ganglia, and they serve as sensory processing areas whose activation initiates spinal motor reflexes as well as sending sensory information to higher brain areas. The larger and more complex the ganglion, the more brain-like it becomes. For example, some insects have ganglia in their heads that are specialized and large enough to merit being called brains. (Unlike some theists, I'm afraid)

Adding still more complexity to the part of nervous system contained in the head is called encephalization. Chordates are animals that have both a brain and a spinal cord. The word chordate comes from the term “notochord” which is the embryonic precursor to the spinal cord. Here’s a kicker for the fundies: both the nervous systems of prechordates like drosophila melanogaster (fruit fly) and chordates like humans are formed under the direction of groups of genes called homeobox gene clusters. These gene clusters specify the organization of the nervous system of both insects and chordates, and so indicate a common ancestor in the lineages. Yep, Schrack’s cousin is a fruit fly and Carico has naught but a ganglion in her head.

In humans, various brain structures (often referred to as ganglia, by the old anatomical nomenclature, as in “basal ganglia”), are comprised of cells with similar cytoarchitecture (structure) and similar functions. There is no “sensible” design to the brain, instead there is both parallel and hierarchical organization, with some structures inhibiting the functions of other structures, and the majority of the brain is composed of interneurons, whose primary function is to integrate incoming sensory input and initiate outgoing motor signals.

It seems that wherever in evolution there were 2 cells to rub together, there was room for specialization of function, which conferred definite selective advantage to those 2 cooperating units of life. The more units that cooperated, the more specialized the functions could become, and the greater the potential for selective advantage, so on and so forth until viola! There are naked apes with big brains. And the xians say we got morality from jeebus! I say it’s in the genes, and it goes as far back as Monera.

I hope you found this helpful... I paraphrased liberally from Kolb & Whishaw's "Introduction to Brain and Behavior" physiological psychology text if you want to read more on the topic.

[calpurnpiso]

scathach wrote

While my input is not so technically elegant as that posted previously, a brain is a lot easier to explain than a wing, I think. It helped me get a grip on the possible sequence of events in the origin (genesis?) of brains by looking at the taxonomic hierarchy as a model of the evolutionary sequence. You can easily see a logical evolutionary progression from life forms such as bacteria (Monera kingdom) to true single celled organisms (Protista kingdom), to multicelled animals (Animalia kingdom). In animals, the cells differentiated to muscles and neurons. Among the simplest of the 15 animal phyla are those with a simple nerve net, like sea anemones and jelly fish. The nerve net (no brain and no spinal cord, just a reticulum of neurons) somewhat resembles the peripheral nervous system of humans, in that it consists of neurons that respond to environmental stimuli, but it also connects directly to other neurons that move muscles. Simple in-out messaging.

The next higher phyla include animals with more complex systems, including a specialized head, body and tail. The body in these phyla consists of a bilaterally symmetrical segmented nerve trunk. The segments are similarly organized body parts, each segment containing both a sensory input and a motor output. The human nervous system is also bilaterally symmetrical as well as segmentally organized (the dermatomes resemble flatworm trunk segments).

http://a248.e.akamai.net/7/248/430/2...res/f165_2.gif(Note that sacral segment S2 serves both the anus and the genitals... oh wait, that was another thread...)
http://www.student.loretto.org/zoolo...oussystems.gif (this one's the flatworm)

The next most complex set of phyla up the list, including clams, snails, squids (except for the far more highly evolved Solidsquid, of course), insects, and octopuses, have ganglia. Ganglia are small clusters of similarly functioning nerve cells that act like simple little brains. Humans have ‘em, clusters of them line the outside of the spinal column, they’re called the dorsal root ganglia, and they serve as sensory processing areas whose activation initiates spinal motor reflexes as well as sending sensory information to higher brain areas. The larger and more complex the ganglion, the more brain-like it becomes. For example, some insects have ganglia in their heads that are specialized and large enough to merit being called brains. (Unlike some theists, I'm afraid)

Adding still more complexity to the part of nervous system contained in the head is called encephalization. Chordates are animals that have both a brain and a spinal cord. The word chordate comes from the term “notochord” which is the embryonic precursor to the spinal cord. Here’s a kicker for the fundies: both the nervous systems of prechordates like drosophila melanogaster (fruit fly) and chordates like humans are formed under the direction of groups of genes called homeobox gene clusters. These gene clusters specify the organization of the nervous system of both insects and chordates, and so indicate a common ancestor in the lineages. Yep, Schrack’s cousin is a fruit fly and Carico has naught but a ganglion in her head.

In humans, various brain structures (often referred to as ganglia, by the old anatomical nomenclature, as in “basal ganglia”), are comprised of cells with similar cytoarchitecture (structure) and similar functions. There is no “sensible” design to the brain, instead there is both parallel and hierarchical organization, with some structures inhibiting the functions of other structures, and the majority of the brain is composed of interneurons, whose primary function is to integrate incoming sensory input and initiate outgoing motor signals.

It seems that wherever in evolution there were 2 cells to rub together, there was room for specialization of function, which conferred definite selective advantage to those 2 cooperating units of life. The more units that cooperated, the more specialized the functions could become, and the greater the potential for selective advantage, so on and so forth until viola! There are naked apes with big brains. And the xians say we got morality from jeebus! I say it’s in the genes, and it goes as far back as Monera.

I hope you found this helpful... I paraphrased liberally from Kolb & Whishaw's "Introduction to Brain and Behavior" physiological psychology text if you want to read more on the topic.

Gratias tibi ago for the info...:) I was wondering if the largest dinosaurs which had a mini-brain in their rear, didn't have instead a form of ganglia?..just curious.

Oh I see now. I always DID view evolution through the individual, not the population, that is probably why it looked like it always got better through intelligence, not being random. But that definitely clears some things up.

However, I still hold more faith that Jebus has a plan for our spirits when we die and that the holy spirit will design animals, yet pick favorites such as humans, to go to heaven and that Jebus has died for my sins and that I can repent with wavelengths that defy the laws of physics. I hope that someday, you too will see this for yourself.

i was wondering, say in a few thousand years when we are alot more advanced, do you think it will be possible for humans to genetically take other creatures best abilities and make one super being, for example, take the sense of smell from a dog, the speed of a cheetah, the radar of a bat, the color changes of a camelion, the brain of a human, the armour of a beetle, the jump of a grass hopper!!??
is evolution already taking us down this path?

baznap wrote

i was wondering, say in a few thousand years when we are alot more advanced, do you think it will be possible for humans to genetically take other creatures best abilities and make one super being, for example, take the sense of smell from a dog, the speed of a cheetah, the radar of a bat, the color changes of a camelion, the brain of a human, the armour of a beetle, the jump of a grass hopper!!??
is evolution already taking us down this path?

no. evolution is not taking us down this path. genetics is. is there something wrong with the path?

(except for the far more highly evolved Solidsquid, of course)

:)

baznap wrote

i was wondering, say in a few thousand years when we are alot more advanced, do you think it will be possible for humans to genetically take other creatures best abilities and make one super being, for example, take the sense of smell from a dog, the speed of a cheetah, the radar of a bat, the color changes of a camelion, the brain of a human, the armour of a beetle, the jump of a grass hopper!!??
is evolution already taking us down this path?

This creature already exists, his name is Chuck Norris.

certain restrictions would apply obviously...but I don't think that humans as we know them will even exist in a few thousand years. And if they did, and somehow created some superbeing, it certainly wouldn't be able to be called "human"

[a different tim]

baznap wrote

i was wondering, say in a few thousand years when we are alot more advanced, do you think it will be possible for humans to genetically take other creatures best abilities and make one super being, for example, take the sense of smell from a dog, the speed of a cheetah, the radar of a bat, the color changes of a camelion, the brain of a human, the armour of a beetle, the jump of a grass hopper!!??
is evolution already taking us down this path?

Evolution isn't but genetic engineering might, I suppose. You might for example be able to introduce genes that cause certain human skin cells to develop into chromatophores rather than melanocytes, giving you colour change, but I don't think this would be easy, those genes might also do other things we don't want, and the surrounding skin cells would need to be set up to accommodate them. The jump of a grasshopper might be rather more difficult, since grasshopper legs work on a totally different principle to human ones, and don't scale up well. You'd need some shock resistance for the G forces as well......

Generally speaking in GM as it stands you introduce one gene which codes for a protein the function of which is fairly well understood. For this sort of thing you're talking about rewriting substantial portions of the genome, which, since gene effects act in combination, is (probably) exponentially more complex. If you want to build a creature from scratch it's even worse. I'd stick to giant robots, personally.

I think it is useful to first look at the embryonic development of the nervous system. Since evolution involves changes in developmental processes which are driven by genes and genes are the unit of selection. I just began to write an overview of neural development but 5 lines in realised it will be way to long a post, and Im a lazy cunt. If anybody is interested, search the following terms.


1. gastrulation

2. Neural induction (mangold and spemann...funny experiments), inducer molecules.

3. neural folds, neural tube (precursor of central nervous system), neural crest (precursor of most of the peripheral nervous system).

4. Interkinetic nuclear migration

5. neuronal migration

6. post-mitotic neurons

7. Axon extension/guidance and neurotrophic theory (why would god make twice as many neurons as are needed in the brain then kill off excess??)


These processes set up the basic anatomy of the brain. From here connections are made and broken (often using the same processes that make and break them during development).

I am NOT saying that in utero we go through all the stages of evolution. I am saying that many of the genes involved in the development of the nervous system are conserved throughout evolutionary time. Gradual extrapulation (increased no.s of splice variants of proteins etc.) and exaptation can slowly build more and more complex nervous systems, via similar methods used in earlier vertebrates. The survival advantages of a more complicated nervous system are obvious to any christian....or are they?

[Gnosital]

calpurnpiso wrote

Gratias tibi ago for the info...:) I was wondering if the largest dinosaurs which had a mini-brain in their rear, didn't have instead a form of ganglia?..just curious.

I am afraid I am not well versed in dinosaur neuroanatomy, but it seems very likely to me that there might have been large caudal ganglia in a really big dinosaur. Are you saying that dinosaur tails had a mind of their own...?