Eyes, Part One: Opening Up the Russian Doll

(The first of a two-part post)

The eye has always had a special place in the study of evolution, and Darwin had a lot to do with that. He believed that natural selection could produce the complexity of nature, and to a nineteenth century naturalist, nothing seemed as complex as an eye, with its lens, cornea, retina, and other parts working together so exquisitely.The notion that natural selection could produce such an organ "seems, I freely confess, absurd in the highest possible degree," Darwin wrote in the Origin of Species.

For Darwin, the key word in that line was seems. He realized that if you look at the different sort of eyes out in the natural world, and consider the ways in which they could have evolved, the absurdity disappears. The objection that the human eye couldn't possibly have evolved, he wrote, can hardly be considered real.

The more scientists study the eye, the more they recognize that Darwin was right. This is not to say that they know everything about how the eye evolved. Evolutionary biology is not an automatic answer machine that can instantly tell you every detail about how eyes--or any other organ--evolved. Instead, scientists study eyes of different animals, the proteins they are made of, and the genes that store their recipe. They come up with hypotheses about how evolution could have produced these results. Those hypotheses then point the way to new experiments. In this way, evolutionary biology is no different from geology or meteorology, or any other science that illuminates the natural world.

To be precise, I should say that scientists study the evolution of "the eye." There are millions of different eyes (and other light-detecting organs), each built by a different species from its own unique set of genes. Closely related animals tend to have similar eyes, because they descend from recent ancestors. Some scientists study how eyes can adapt over a few million years to the special circumstances of a particular species. Other scientists step a little further back, to look at how the different types of eyes have evolved from simpler precursors. And other scientists step even further back in time, to find clues about where those simpler precursors came from. In this post, I will move back through time through these different stages of eye evolution (a la Richard Dawkins's The Ancestor's Tale.)

Humans have what's known as a camera eye. Light first passes through a cornea, which refracts the light. It then passes through a lens, which refracts the light further, so that it forms a focused image on the retina. We are primates, and so it's not surprising that all other primates have a similar type of eye. But different primates have important differences in the shape of their eye. Nocturnal primates have wider, more curved corneas than primates that are active during the day. A wider cornea lets nocturnal primates make the most of the moonlight by allowing more of it into the eye. Primates active during the day benefit from small flat corneas probably because the lens can sit further forward in the eye, producing a sharper image. This arrangement doesn't let as much light in, but during the daytime, that's no great loss. Chris Kirk of the University of Texas analyzed primate eyes in the December 2004 issue of The Anatomical Record (he has posted the paper on his web site).

For the most part, nocturnal and diurnal primates fit the same patterns as other mammals. But monkeys and apes (including humans) turn out to have extremely small, flat corneas, even compared to other primates that are active in the daytime. Kirk argues that this particular group of primates (called anthropoids) has experienced natural selection that has produced even sharper vision than found in other mammals active in the daytime. Other aspecsts of the anthropoid eye also make it sharp, including its fovea, a small spot on the retina that's incredibly dense with photoreceptors. In fact, anthropoids are matched only by raptors for their sharp vision. It's possible that our ancestors evolved such sharp eyes for hunting insects; monkeys and apes are also extremely social animals, and they rely on their keen eyes to look at one another and pick up subtle cues in their faces. Our ability to make sophisticated tools may have been made possible by the evolution of tiny corneas.

Changing the shape of an eye requires changing the molecules that make it up. Molecular fine-tuning can also alter an eye's ability to block out UV rays, to refract light at different angles, or to become more sensitive to different colors. Despite the fact that all vertebrates share the same basic eye plan, you can find a wide range of molecules inside them. Some are found only in fish, some only in lizards, some only in mammals.

How does one group of animals evolve one of these new molecules? One way is to borrow it. Joram Piatigorsky of the National Eye Institute and his colleagues have identified many of the molecules that make up the lens and cornea of humans and other animals. These molecules are practically identical to molecules found elsewhere in the body. Some are essential for the development of the head in an embryo. Others protect our cells from heat and other stress, others detoxify poisons that would otherwise build up in the blood.

Originally, the evidence indicates, many of the molecules found in eyes today were only produced in other parts of the body. But then, thanks to a mutation, the same gene began producing its molecule in the developing eye. It just so happened to have the physical properties that made it well suited to being in an eye. In later generations, natural selection favored mutations that made it work better in the eye.

But this new job in the eye may have posed a trade-off for the molecule's original job. Further fine-tuning may have only been possible when the gene went through a particularly drastic (but common) mutation: it duplicated. Now one copy of the gene could adapt to the eye, while the other continued specializing in its original job. (I wrote an essay a couple years ago about some of Piatigorsky's work in Natural History.)

Darwin didn't know about gene sharing or gene duplication, but he still managed to make some important observations about how the human eye could have evolved from a simpler precursor. Early eyes might have been nothing more than a patch of photosensitive cells that could tell an animal if it was in light or shadow. If that patch then evolved into a pit, it might also have been able to detect the direction of the light. Gradually, the eye could have taken on new functions, until at last it could produce full-blown images. Even today, you can find these sorts of proto-eyes in flatworms and other animals.

The closest invertebrate relatives of vertebrates fit nicely into Darwin's predictions. Amphioxus, which looks like a sardine with its head cut off, lacks a true brain or camera eyes. But the front end of its nerve cord is slightly swollen, and is built by many of the same genes that build a human brain. What's more, they grow a pit lined with light-sensitive cells which they seem to use to navigate through the water. The genes that build this pit are nearly identical to the ones that build our own.

The fact that Aphioxus has such a simple precursor to the vertebrate eye might suggest that this organ evolved from scratch. Yet eyes can be found on many other animals--which was how Darwin first figured out what a precursor to the vertebrate eye might have looked like. Eyes can found in insects, squid, and many other animals. Did they evolve independently?

The answer is yes and no. In the 1990s, Walter Gehring of the University of Basel and his colleagues discovered an essential eye-building gene called Pax-6 that was shared by insects and humans. If he inserted the human version of the gene into a fly larva, he got fly eyes popping up all over the fly's body. Gehring has proposed that Pax-6 is a master control gene, switching on an entire circuit of eye-building genes. In insects and in humans (and in all of the animals that share a common ancestor), this circuit builds eyes. But in each lineage, a different set of genes have been incorporated into this circuit, so that they can build eyes as different as the compound eye of an insect and the camera eye of a human.

The simplest explanation for so many animals sharing this same circuit is that they all inherited it from their common ancestor--a small worm-like creature known as a bilaterian that might have lived 570 million years ago. Exactly what sort of eye these genes produced in the Precambrian mists of time isn't clear, though. And until last fall, another feature of the eye didn't seem to fit this hypothesis: its photoreceptors. Invertebrate eyes and vertebrate eyes use different photoreceptors to sense light. But researchers have found that both kinds of photoreceptors grow on a humble animal known as a ragworm, which is believed to have branched off very early in the evolution of bilaterians. It's possible that the ancestor of living bilaterians produced both kinds of photoreceptors. One kind was lost in the vertebrate lineage, and the other was lost in the lineage that led to insects and other invertebrates with full-blown eyes.

Yet eyes are not limited to bilaterians. Jellyfish belong to a branch of animals known as cnidarians that split off from the ancestors of bilaterians some 600 million years ago. Some species have simple photoreceptors, while others have full-blown camera-eyes hanging from their tentacles. Biologists want to know whether these eyes evolved independently, or share some of the ancestral toolkit that produced human eyes and fly eyes. One hint that they share a common heritage is the fact that some of the genes that jellyfish use to build eyes bear a striking similarity to Pax-6 and other genes that build bilaterian eyes. On the other hand, most cnidarians (such as sea aneomones and corals) don't have eyes. What's more, jellyfish eyes are pretty weird compared to bilaterian eyes--for one thing, they don't wire up to a brain. The larvae of one species grow photoreceptors that don't even connect to a neuron. The photoreceptors link instead to hair-like structures in the same cell. Presumably light triggers these cells to flail their hairs to make the larva swim.

In years to come, the search for the roots of eye evolution will push even further back in time. In a paper in press at the Journal of Heredity, Walter Gehring points out that the first component of animal eyes to have evolved was the photoreceptor--a molecule that could catch light and turn it into a signal. One model for the origin of animal photoreceptors comes from colonies of algae, many of which have "eyespots" that allow them to swim towards the light so that they can photosynthesize. Perhaps early animals lived in colonies as well and had similar eyespots. Later, these simple photoreceptors evolved pigments and other molecules that helped capture more light, and eventually became able to form images.

But Gehring also proposes a weird but compelling alternative: our ancestors stole their eyes. Many times over the course of evolution, organisms have been engulfed by larger organisms, and the two have become integrated into a single being. Our cells, for example, contain mitochondria that we rely on to generate energy; originally, these were free-living oxygen-consuming bacteria. Another important fusion took place over two billion years ago, when bacteria that could carry out photosynthesis were consumed by an amoebae-like host. The bacteria then became a structure called the chloroplast, which can be found today in trees and other plants, as well as various sorts of algae. Increidbly, some of these algae were engulfed by other algae, which also came to depend on the photosynthesis carried out by the bacteria. Gehring likens these organisms to Russian dolls, with the original bacteria nestled deep within other organisms.

It's likely that before the bacteria were consumed again and again, they had already evolved a light-sensing molecule that helped them harness sunlight--perhaps by acting as a biological clock. The algae that devoured the bacteria may have retained the ability to sense light for the same purpose. Gehring points out that one group of these algae--dinoflagellates--have fused with corals, jellyfish, and other animals. It's possible that early animals may have incorporated the genes for light-sensing in their own genomes. If he's right, we gaze at the world with bacterial eyes.

Coming next: Once the eye evolves, what does it take for it to disappear?


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One of things I always thought was interesting about the Pax genes that encode for the sensory organs, is that they are the same genes that play a role in the formation of the gut. I once heard an eloquent explanation by one of my professors (that I lack the ability to reproduce) that the eye may have evolved in concert with some of the digestive system, since, after all, vision allows for the efficient capture of food.

By Yuri Guri (not verified) on 15 Feb 2005 #permalink

Human eyes are among the best arguments against "Intelligent Design." How intelligent was it to mount the sensor cells backward underneath a hunk of meat, nerves, and blood vessels? How intelligent was it to leave a big hole (the "blind spot") near the center of the field? Such "intelligence" inspires neither awe nor worship.

By H. John Caulfield (not verified) on 23 Feb 2005 #permalink

I think I learned last semester that gene duplication does not "free up" the original gene, but instead that both genes continue to change at a similar rate which is faster than genes are not duplicated. Doesn't make much difference to the story, but I thought I'd point it out in case it does matter some time.

I've read about the Pax-6 gene, most notably in Gerald L. Schroeder's "The Science of God." Schroeder addresses the presence of Pax-6 in at least five out of the six phyla with visual systems, the sixth being a phyla that hadn't been studied at the time. But the probabilities are "astounding" to have occured individually in each phyla by chance, with a human-incect similarity of 94% and a zebra fish-human match of 97%. Given twenty amino acids with one hundred and thirty spaces on the Pax-6 gene, there would be one in ten to the one hundred and seventieth power combinations. With five different phyla that have the Pax-6 gene, that would mean the probability of each phyla producing the same Pax-6 gene independently would be one chance in ten to the one hundred and seventieth power raised to the fifth power.

By Adam Yoho (not verified) on 02 Mar 2005 #permalink

In regard to Adam's comment: It is not necessary to invoke some supernatural agency to explain Pax-6 in various animals. They inherited it from a common ancestor--just as my brother and I have inherited nearly identical eyes from our parents. Just because our eyes are very similar doesn't mean that a supernatural event took place.

I'm used to debating, so sorry if I'm misusing this system. But, the funny thing is that the very next paragraph in the book says: "There is no way this same gene could have evolved independently in each of the five phyla - it must have been present in a common ancestor. The gene that controls the development of eyes was programmed into life at the level below the Cambrian. That level is either the amorphous sponge-like Ediacarans or one-celled protozoa. But neither has eyes." I haven't looked into this, but it does seem like a fairly accurate observation.

By Adam Yoho (not verified) on 02 Mar 2005 #permalink

It's NOT my understanding that the "level" of animals or multicelled creatures "below" the Ediacaran consisted solely of sponges or protozoa. While I don't have handy references or links, don't the genetic inferences and the fossil record of tracks and traces suggest that there were several hundred million years of earlier evolution of VARIOUS soft-bodied phyla, who might well have been in the course of evolving light-sensing systems?
In fact, I recall a proposal that the "explosion" and the need for hard body parts in predators and prey may well be linked to the development of vision. If so, then a complex and diverse group of animals were competing away in the several hundred million years leading up to the Ediacaran. Vision doesn't require a supernatural nudge or insertion to explain away a "disconnect" between the sponges and the floresence of hard-bodied animals with eyes--vision instead could well have been THE (or one of several) "killer app(s)" evolved by the group of soft-bodied not-simply-sponge animals that were ancestral to the Ediacaran era.

By Steve Russell (not verified) on 03 Mar 2005 #permalink

Here is the citation to the author who has proposed a strong link between the evolution of vision and the Cambrian "explosion":
Andrew Parker: In the Blink of an Eye. Perseus Publishing 2003

By Steve Russell (not verified) on 03 Mar 2005 #permalink

I'm not going to argue my ideas too much with others who are more educated in this matter than I am, but I found a video presentation of Andrew Parker on darwincentre.com addressing In the Blink of an Eye. Parker states that before the evolution of hard parts within organisms, there is no support from the fossil record on previous hard parts. I'm pretty sure I'd be correct in assuming that scientists attribute this to genetic mutations and dormant genes coming out when needed. However, I also stumbled across an interesting article called What's Driving Evolution by Chris Ashcraft on nwcreation.net; there he poses a very interesting question: Since we know all the various breeds animals were created through genetic recombination, why are we taught every variation of animal in nature is a result of mutations? Most scientists would acknowledge that mutations are very rare, let alone mutations that benefit the organism and help it to survive. But would it really be logical to support theories on mutations accounting for all the diversity of life when other mathematical theories one also supports conclude that those possibilities are impossible?

By Adam Yoho (not verified) on 03 Mar 2005 #permalink

Also, as follow-up, Parker confirms that out of the thirty seven or so phyla, only six of them have visual systems, and he says that scientists are leaning towards the theory that each phylum evolved eyes separately, contributing to my previoiusly said probability of this happening.

If you're getting all your info on evolution from creationist websites, it's no wonder you're a little confused. I find this statement to be amazing: "[B]efore the evolution of hard parts within organisms, there is no support from the fossil record on previous hard parts..." What does that say again!?! Of course there's no support in the fossil record of hard parts before hard parts evolved! And before humans evolved, there's no archaeological record of artifacts of technology either. This tautological statement isn't a coherent criticism of evolution--it's barely a coherent statement!
If the creationist you're quoting is trying to put together a testable hypothesis here, it's buried too deeply in the wool that he's pulled over his own eyes. Let's reformulate: how could animals without hard parts evolve hard parts, perhaps? I haven't done any recent reading in this area, but minerals like calciums and phosphates are utilized by cells for many structural and metabolic purposes in concentrations that are extremely unlikely to fossilize. So we're not talking about going from cells without the capacity for channeling/sequestering concentrations of minerals to cells that can--initially, we're probably just talking about changes in the degrees of concentrations.
Now we're ready to start hypothesizing, then looking for evidence. You sound like a smart guy who knows how to run a search engine: why don't you go somewhere (other than a creationist site, since they don't understand the falsification of hypotheses...) and see what the possible pathways for this kind of evolution are?

By Steve Russell (not verified) on 03 Mar 2005 #permalink

Actually, although no I didn't type it correctly, I said that "Parker", hence Andrew Parker, stated that there was no evidence of hard parts before the Cambrian explosion. Then Parker said that "if you look at the fossil record before that, and there's literally nothing; no hard parts at all." These hard parts seemingly came from nothing, or "mutations" I addressed also. Even the University of California's evolutionary curriculum finds "[r]andom mutation [a]s the ultimate source of genetic variation." Although I can admit I haven't researched mineral concentration in such early organisms either, so I don't have enough information to give comment. As for my sources, I do have creationist sites, but I do also have evolutionist sites as well, namely Talk Origins Archive which I wouldn't doubt you know of already, and also The Panda's Thumb has some interesting articles.

I must ask you one question though, since there isn't a reasonable explanation to that I know of: How did sentience evolve?

One description of mechanism resulting in sentience is found in Antonio Damasio's "The Feeling of What Happens." Though he didn't try to explain the development of the machinery, just the machinery itself, I recommend the book.

Doesn't it seem proper that an organism would have a better chance of perpetuating "self" if it recognized that "self" existed? Continued investigation of the wetware will result in clearer understanding of the mechanism
and its roots.

Although couldn't one conclude that it would require "self" for an organism to know "self" existed? If that assumption would be correct, then it would have already been sentient before it realized this, so it would seem impossible to trace back to where sentience "evolved." I am curious, though, as to how a state of mind if you will, could evolve in an organism with its implanted aspiration to be better than what it is. To me it just doesn't seem like there's a logical explanation to it.

Sentience comes and goes as evidenced by loss of consciousness in sleep, injury or by chemical means in anesthesia.

The machinery is subtle and difficult to observe. This does not mean that it is necessarily supernatural or irreducibly complex.

Personal experience of consciousness is an internal, subjective attribute and not shared therefore not directly available for objective evaluation. But there are external signs which accompany the symptoms of consciousness. Damasio offers multiple instances to show correlation between objective, observable brain function and the associated subjective reports.

I find it quite likely that the degree and variety of consciousness I have experienced, including sleep, concussion and alcohol induced euphoria/stupor may be mapped to intracranial chemical reactions rather than soul. I also find it likely that a similar variety of consciousness can be found among other animals. I believe my dog is conscious: he sleeps and can converse with me in a limited fashion. I don't see that my fish is anywhere as communicative. I see no reason to disbelieve that varying degrees of sentience are impossible among ancestors who share in differing degrees the chemical mechanisms which provide it. The source of these differences in chemistry and structure are inherited (fish vs dog vs me) and thereby accessable to natural selection.

My comment regarding the usefulness of the internal representation of "self" was intended to spark understanding. "Self" would be highly selected for as an individual posessing a knowledge of "self" can then protect it"self".

My perspective of sentience is different than its definition of "consciousness" as you addressed; I see it as what makes humans human. What drives us to being better than what we are. I'm not talking about just being aware of your surroundings, because all organisms can do that. Humans, however, are completely different than all other animals. We have the ability to reason, which sets us apart from every other organism. That's what I see as impossible to contribute to evolution.

Whatever you want to call it, "consciousness," "sentience," "the ability to reason," or just (JUST?) "being aware of your surroundings," the point is that these abilities exist on a spectrum across the living world. You present no evidence for your notion that humans' ability to reason is completely different from the abilities of other animals--different, yes; more and "better," perhaps; but "completely" different, on what scale, why, and how?
Frankly, I see animals "reason" their way through "problems" all the time--no "instinctual" set of instructions, however detailed and however acquired, can possibly provide any creature with an exhaustive moment-to-moment program for how to get through the challenges of any given day--in a manner that, were I on the inside looking out, I would expect would feel very much like my "reasoning" feels to me.
Again, as with the typical creationist argument, you set up a difference that you regard as one in kind, rather than one in degree, and therefore refuse to "contribute" [attribute?] the difference to evolution. Evolution, allegedly, can generate small or inconsequential differences, but not really big important ones. With the creationists, that's it, end of story. No amount of evidence can move them from their intitial conclusion. In your case, I would hope you are at least willing to stay open-minded. If evolution created all the other variation in living things, we may be able to lay out a plausible case--backed up with persuasive evidence--for how it crossed what you see as the "sentience" divide.
What's the creationist, Id-ist, etc., do at this point? Throws his or her hands in the air, gives up, takes the marbles and goes home. Worse still, argues (legislates, lobbies school districts) that everybody else should give up too. Let's keep attacking the problem from diferent angles. Hey, let's actually USE our vaunted "reason," just for the heck of it. Birds have beaks that have evolved to crack nuts. Maybe we have evolved reason to crack THIS particular nut, eh?

By Steve Russell (not verified) on 07 Mar 2005 #permalink

Well obviously I can't present evidence that animals can reason just as well as humans or that they use intellect to get through situations. But from what I can tell, you still don't seem to understand my view of sentience, although I don't know how to explain my view of it. As for the rest of your post, I couldn't really follow it because it just seemed too erratic so I don't really have any idea what you were trying to say.

Sorry to hear that you cannot "explain my[your] view of it[sentience]" It makes discussion difficult. However I do agree that the definitions of terms are crucial to mutually comprehensible discussion.

For instance, can you define your use of the phrase "drives us to being better than what we are." Saying that "everybody knows" is not sufficient. Are we "better" than a vulture? We are certainly not faster, nor can we see as well. But we have much more dexterity with our forelimbs. Isn't "better" dependent on the context?

When you can take a swing at a definition of "sentience", I'd be interested in hearing it as well.

Well when I talk about us trying to be better than what we are, I mean along the lines of making your life better and trying to make the world better and creating an influence. I'm not talking about things that can be explained with evidence and scientific proof and all that, which I know drives evolutionists and scientists crazy because the last thing they want to do is rely of faith to explain something. But I don't recall seeing alligators helping along a baby turtle across a river just to be nice; obviously animals such as that haven't really been observed being "nice." So no, when I'm talking about becoming "better," I don't mean we'll be "faster," "stronger," etc. Humans have the capicity of knowing what is right and what is wrong, most of the time. Other animals don't have that.

I'd say then that's part of my definition of "sentience." However, as most of you have no doubt learned by now in debating about this subject, I don't doubt that most of the time my views you probably won't be able to understand, although definitely not by lack of intelligence, or it just won't seem logical to you. My view is based primarily on faith while yours is based on scientific evidence, so this argument is going to get too far, especially with my personal experience debating this. Although I know my mind is open, so you don't have to worry about that.

"so this argument is going to get too far" is supposed to be "...isn't going to get too far." Sorry, I missed it.

Adam, there is--believe it or not--an extensive scientific literature around the evolution of altruism, morality, parenting behavior being extended to non-offspring, and the like, going back to some of the early ethologists, E. O. Wilson, and others.
And don't be too dismissive about the kind of behavior of which non-human predators are capable. There was a recent NPR/BBC story--verified by the BBC journalist--of a lioness literally lying down with and exhibiting protective/caring behavior toward an infant oryx (antelope-type herbivore). Normally these two species are in a distintly different kind of relationship, of course, but nature is capable of amazing things.
I've now gotten a couple of links, assuming the comment system will let me post them (and sorry for the lack of a "compressed" link). Or you can do your own search with words like "lioness baby antelope" etc.

By Steve Russell (not verified) on 10 Mar 2005 #permalink

Adam, why have faith in faith?

Given your faith in faith and my lack of faith in faith, who has the True truth?

Faith is simply the inability to consider the proposition that you might be wrong.

Hm, wow. DH, I must honestly say I've seen similar arguments from 13 year olds. Why do I have faith in faith? I'd say since I can consider the possibility of something that's, God forbid, better than me. As I have said before, why support a theory with probabilities that any evolutionist will tell you to be astronomical to say the least?

It's amazing how that every person or group I debate with, including the above-mentioned 13 year olds and such, the evolutionists always attack my view first. I try never to attack their view since I'm trying to present my ideas, but it never fails that when I try to present my case, I am either insulted or my view is just openly attacked, few times do I actually get an argument back. While you all have been a good deal better than elsewhere, I thought I wouldn't have to deal with comments such as your definition of faith.

Those of us who come here primarily to drench ourselves in the latest cool science Carl has pulled together can get awful tired of the typical creationist "trolls," who merely pontificate, without adding anything new or useful.
In the last month or so, we've had a couple of "persons of faith" drop in on the discussions who have at least claimed to be open-minded about the creationist vs. evolution "debate." They have not merely parroted the creationist jibber-jabber. Whether we agree with what they're saying or not, it's been my feeling that we ought to take a bit more of a respectful tone with them than we often find ourselves taking with the same old trolls.
Everybody's entitled to their opinion of course, but Adam strikes me as one of these non-trolls, and thus deserving of some basic respect and politeness.
This having been said, Adam, if--when all is said and done--it turns out that ALL that you're bringing to the table is your declaration of faith, and it appears that you're not really participating in the scientific give-and-take, beyond reiterating that you can't accept this data or grapple with that data because of your faith, then I think you need to expect to be challenged by someone like DH. I didn't find his comments rude or ad hominem--he's just trying to push you a little to see HOW your faith is going to play into your participation here.
I've got no problem with Adam having faith and having some perplexities about evolution as a result. But I've also got no problem with DH pushing a little, to see what ELSE Adam might bring to the discussion.
Let's be a little less suspicious of each other, and see if we can't build a dialogue.

By Steve Russell (not verified) on 11 Mar 2005 #permalink

Well thank you Steve, that right there reminds me of how much better it is debating here than most other places. For your articles, I hadn't known about such documentation, so thank you for sharing that. Apparently my thinking that no other animals are "nice" to each other was inaccurate, so I apologize. However, I would like to address something else - evolution by random chance.

I thought this one page was informative about looking at probability.
Despite having a religious-based title, the numbers are definitely not biased. Also, this site is the best one I have come across so far, with probabilities, and sources for their statements.
Although, I'm only about 1/8 of the way through a list of links and it's 1:30 in the morning, so I'll probably post a few more later.

Hmm. Adam, I'm not quite sure how random chance worked its way into the conversation, since the last I recall we were talking about sentience and altruistic behavior.

In any event, most "religious" (i.e., creationist) sources throw out "random chance" probabilities in an effort to show that the universe won't last long enough for random chance to generate the exact right sequence of mutations to produce a given gene coding a given, biologically-useful protein or behavior.

The sheer probabability info given may or may not be correct. The underlying problem, though, is that--while evolution certainly includes some random phenomena at the variability-generating end of things--it is not a random process at the natural selection end. This renders all the probabilistic data rather irrelevant.

Some very smart people back in the '30s and '40s (Fisher jumps to mind, though I am working from memory) ran these kinds of scenarios, factoring in very small numbers to represent a bias in a given direction imposed by the selection process of a given environment at a given time, and evolution works out just fine probabalistically.

Perhaps a good place to start thinking about this is at the very early stages of the process of "domesticating" amimals or plants (the domestication of pigs from wild boars has been in the papers recently). Although later in the process, humans can be presumed to have realized the benefits and applied deliberate or intentional selective pressure to "breed" the plant or animal in question, early on the process appears to have been driven in most cases by the happenstance interaction of two species busy going about their own lives--the wild boars rooting for fodder amongst the waste that collected around human settlements, or wild corn or wheat precursors preferentially seeding themselves near settlements as a byproduct of human foraging activities.

The human foragers tended--without having any initial "motive" to breed wheat--to conserve their food-gathering energy by "selecting" those grasses with the most easily-accesible seed heads. The boars possessing slightly more "juvenile" traits (making them less wary and more curious) would be more likely to approach human settlements to exploit the available source of garbage (see in this connection Carl's post on animal "personalities").

Once such pressures spring into being, they are going to drive the process of selecting among the available (to some extent randomly-generated) variants in a NON-RANDOM manner. More "juvenile" boars are favored in the vicinity of human settlements. More seed-heavy grasses are accidentally sown in the vicinity of human settlements. The tendency for humans to settle in particular (pig or grass-seed "heavy") locales--as opposed to maintaining more nomadic lifestyles--may itself be slightly favored. Heck, perhaps sharper-eyed or softer-voiced HUMANS are also "favored." At some point, of course, the process becomes "captured" after some bright human discerns what's going on.

If the human element makes these "directed" examples less persuasive, then shift your thought to any of the famous co-adaptations, between insects and flowering plants, for example. As long as ANYTHING about the interaction between two species favors a given direction in selecting from the available variation, the process of evolution becomes a non-random one. Since any given environment at any point during the evolution of life is always going to favor some sorts of phenotypes and behaviors over others, the result is a process that is NEVER going to be purely "random." So the sheer probability numbers mean little in this context, however accurately they might express the tumbling of dice...

By Steve Russell (not verified) on 14 Mar 2005 #permalink

Well I moved on from sentience and altruistic behavior because I tried to explain my view of sentience, with no success, and I stated that my view that no other animals were altruistic was inaccurate. So what more do you want?

But yes, it's pretty much common sense that if something does well in a certain area, it will remain there and become "favored." However, while what you discussed does pertain to natural selection, I see little connection with natural selection's influence in macroevolution.

I can understand and accept the basic concept of natural selection, but it is the belief that natural selection/random mutation is responsible for creating the diversity in all the species that I do not agree with. The concept of natural selection doesn't deal with the genetics; it deals with an organisms adaptation to its environment. If that adaptation isn't genetic (which it isn't), then that organism has no way of producing the same adaptation within its offspring and the cycle must restart.

Genetic mutations, which do alter the genetic makeup of the organism, are rarely beneficial and often actually result in the organism's offspring being less diverse than itself. Think about two birds that are isolated on an island. The birds' offspring would statistically have 50% of the father's characteristics and 50% of the mother's characteristics. This leaves the offspring with half of its parents' genetic makeup combined, which may seem like it would promote diversity. However, as there are more and more offspring, since there are no more characteristics to add to the gene pool, all of the birds that eventually live on that island will all have the same characteristics, just slightly varied. If that's so, and you trace it back to a common ancestor, how did even a group of them evolve into all of the organisms you see today?

Adam, I'm all for discussing this stuff with an open mind. But I'm not sure a blog like this is the best place to learn the basics of genetics and inheritance. There's good college texts for that. Suggetions, anyone?

By Steve Russell (not verified) on 14 Mar 2005 #permalink

Some of those 13 year olds are pretty sharp.
Can God make a rock so big even he can't lift it?
So far I haven't seen any theologians answer this without begging their proof.

I personally have never been able to get past the halting theorem, or Godel's incompleteness to determine how God know (s)he's God. Someone much smarter than I will have to do that.

Perhaps a 13 year old.