Tell us what you know about the theory of evolution without using anything but your own brain.

I thought about opening this thread in IMHO or MPSIMS, but if the thread gets any legs at all I’m sure a discussion will break out so I decided not to bother. I opened the thread here rather than in GQ because my primary interest is seeing what people hereabouts know about evolutionary theory. A couple of comments:

[li]For obvious reasons, please don’t go to, Wikipedia, or any other reference sites until you have made your first response to the thread. In fact, if you could refrain from links and citations in your first response, that would be great.[/li][li]Please also make your first response in the thread without reading other responses to the OP. [/li][li]Once you’re past your first entry, cite (and call for cites) to your heart’s consent. Likewise, you may point out errors, misconceptions, incomplete ideas, and misleading statements in previous posts. Just try to leave your swords in their scabbards, revolvers in their holsters, and axes in whatever you store your axes in.[/li][/ol]


OK, here is what I think I know about evolution.

a) All physiological structures are coded for in DNA, and all DNA is inherited directly from one’s parents via meiosis (whereby you get a haploid set from each parent, adding up to a full set of chromosomes of your own). Hmm that’s not quite accurate; it’s true for sexually dimorphic species but… OK, non-sexually-dimorphic life forms inherit all of their DNA from their (one) parent organism.

b) However, mutations occur spontaneously, thereby allowing for organisms to end up with DNA strings that were not truly inherited at all. These in turn may not manifest themselves in any appreciable manner until several generations later.

c) All characteristics that are physiological, or are epiphenomenae of physiological structures, have a potential impact on fitness for survival. Some of these characteristics may manifest at the individual level (the tendency of an individual to run faster etc), some may manifest interactionally and yet contribute to the likelihood of individual survival (the tendency of a group to take care of young individuals, etc). Individuals less geared towards survival are statistically less likely to survive long enough to pass on their own DNA via reproduction.

d) Over time, DNA that thrives is that which was better geared towards survival as described in c) above; DNA that disappears from the gene pool is that which keyed for traits that made individual survival less likely as described in c) above.

It’s pretty simple. When an organism reproduces, it’s offspring aren’t exactly the same as it. Some differences (in a given environment) are advantageous, some are disadvantageous. Advantageous mutations are more likely to last, and get passed on to further generations.

Starting off …

The theory of evolution (henceforth TOE) is the dominant biological model for the existence and diversity of species on planet Earth. Its primary components are the notions of common descent, inheritance and modification, and survival of the fittest.

Common descent means that all life forms currently in existence share a single primordial ancestor. Over the eons since life began, the lineage of that ancestor has spread, changed, and branched out. The more recently a given pair of species separated, the more closely they are considered to be related and the more similar they are likely to be. Nevertheless, humans, aardvarks, starfish, planarians, and bacteria all descend from the same stock.

Inheritance and modification means that the physical features of an organism derive from its ancestors–most immediately its parents or parents. Such traits are transmitted through DNA, a self-replicating molecule present in the genes of all living creatures. Because DNA does not always replicate perfectly, over time more and more variations are created in a population.

Survival of the fittest means that organisms in a given species and population are obliged to compete for the opportunity to reproduce; this is because of the scarcity of resources, and often because of less-than-infinite breeding opportunities. Because of the differences in DNA in a given population, no two organisms are identical (except for identical twins) and thus bring different advantages and weaknesses to the table. If a given organism possess a feature that makes breeding more likely in given conditions, it will pass on its genes in greater number than other individuals. Likewise, a given organism may possess features that inhibit its chances to breed, which will result in said features becoming less prevalent over time. Because conditions in the environment change, features that are useful at one point may because liabilities later, and vice versa.

Evolution is not telelogical; there is no ultimate aim or purpse to it. Humans are not more highly evolved than chimpanzees, parakeets, or even parameciums; they are just differently evolved.

The TOE is silent on the existence of God or gods. It is conceivable that no deities exists and that that evolution alone accounts for the diversity species; it is also conceivable that supernatural agents use evolution to cause species to grow, flower, separate, and die out. The TOE works either way.

environmental factors cause certain traits to have comparative advantages over other traits in a given population - over time, the traits with such competitive advantages become common and become a characteristic of the population overall.

Populations adapt to suit their environments. Characteristics which increase a creature’s chances of reaching breeding age are obviously more likely to be passed on to the offspring. Over generations, these beneficial characteristics become the norm. On top of this, environmental pressures can divide populations and they can subsequently go their separate ways, happily breeding and adapting like rabbits (especially if they are rabbits :slight_smile: ), until members of population A can’t breed with members of population B anymore. This is called Speciation. That’s basically it.

Various variations and mutations appear in the DNA of all organisms. When a certain such variation or mutation has a positive effect on the survival of a certain population of creatures in a certain place and time, it can become more common in that population. As a result, after many generations, the DNA of that population can be altered significantly from its original form. The process is lengthy, imprecise and essentially directionless, with many “dead ends” along the way.

How’d I do?

I have an issue with the bolded sentence; it needs additional qualification. I can easily imagine the existence of traits which help an individual reach breeding age but which makes it less likely that said individuals will reproduce. Also, I think you need the word heritable at the beginning of the sentence.

Anybody smarter than me think otherwise? (Because I know there’s dozens of Dopers smarter than me, though few prettier.)

Biogenesis is life that occurs without “parents” or previous ancestors, basically the “first” life. At least one event of biogenesis happened on earth, which all living things are descended from.

Each generation has a chance to be slightly different than previous generations, causing variations. Over time, these differences cause species to branch out and create new species. The closer your species’ branch is to another species’ branch, the more closely related you are. Humans are closely related to apes. Apes and humans are more closely related to dogs than fish. Apes, humans, dogs, and fish are all more closely related to each other than they are to plants, but if you go back far enough every organism on the planet has a common ancestor.

  1. Evolution = things change over time. Abundant evidence exists that evolution has occurred at all levels, from the universe as a system to individual lifeforms. The geologic record shows that composition of the atmosphere and surface features of Earth have changed considerably over time. There is fossil evidence of numerous lifeforms that were once widespread but now are extinct or greatly changed in form from that of their ancestors.

  2. An aspect of evolutionary theory that seems to be a point of contention for many is the theory of natural selection, which, among other things, posits that lifeforms tend to evolve based on a combination of mutations at the cellular level and environmental pressures, into other lifeforms that nevertheless share a common ancestor. Considerable evidence exists for a process of evolution through natural selection, although not every link in the evolutionary chain has, or can be, identified.

How’d I do?

I have read the OP then hit the “end” button to avoid reading anyone else’s responses. Apologies for inaccuracies, and hoping for pointers where I have stuff wrong.

So, we have a planet that, several billions of years ago, was chugging along with water and geysers and volcanic activity. Due to the circumstances, various molecules are being formed and destroyed on a very regular basis. Some of these, amino acids, are robust molecules, and in certain reactions they bond with each other and form proteins. A few of these proteins have self-replicating qualities, and are in the circumstances to do just that. This is abiogenesis, but not necessarily life.

[I am very ropy about the next part…]

After a few million squillion years, these self-replicating proteins have become so complex that they have bonded together in myriad reactions and eventually some of them have become ribonucleic acid (RNA) and deoxyriobnucleic acid (DNA), which are supremely robust self-replicating molecules, that also contains complex information about that self-replication. A single unit of informational coding on the double-helix of the DNA molecule is known as a gene.

Through the process of self-replication, mutation, and “survival of the fittest”, various forms of DNA begin to appear in extremely complex forms - the DNA allows complex structures to arise around itself, and we see for the first time things that resemble cells: simple bacterium-like lifeforms that have an outer protein shell, and an inner nucleus that contains the important DNA. Other protein molecules arise within these structure to maintain it.

[At this point in my explanation, I myself am starting to believe in Intelligent Design…]

From the start these unicellular “lifeforms”, which, due to mutation, can be very different depending on their circumstances, interact and compete. Many die out, but some of them also end up in symbiotic relationships with their peers. In particular, one RNA-based structure becomes incorporated into a larger DNA-based structure, and this symbiosis proves extremely productive: the RNA-based “bacterium” becomes what we now know as the mitochondrium, a structure which coexists within the nucleus of a cell, and provides proteins that service and maintain the instructions of the DNA.

Over billions of years, thanks to environment, mutation and selection, unicellular organisms become more and more complex, for example, some growing scillia (hairs) for propulsion, light-sensitive structures, simple food-sensing parts. Meanwhile the symbiosis between the various unicellular organisms continues, and gradually colonies of these cells become indistinguishable from multicellular organisms.

At this time, all evolution was in the sea, and these organisms, with various appendages and tools, created from mutation and selection, spread throughout the seas. Each organism, over generations, adapts and changes successfully, but the majority die out. At some point [and I have no fucking idea when, or if I’m even correct], the method of replication alters: where cellular organisms replicated by splitting, some multicellular organisms developed two different kinds of the same organism, bearing different DNA codes (known as “chromosomes”). The chance for genetic alteration and mutation was greatly increased by this shift, leading to what we know as sexual reproduction, and organisms that developed this tended up adapt faster than asexual reproducers.

Meanwhile, for many organisms, the amount of information - the genes - contained on the self-replicating DNA molecules increased and increased, and the complexity of the lifeforms increased too. Gradually, these creatures developed structures that allowed them to reach to all parts of the oceans, and eventually they evolved structures that allowed them to leave the oceans.

Through the same process, multitudes of what we know as plants, and what we know as animals, flourished in the oceans and on land, continually mutating, colonising, working in symbiosis, and adapting. Almost all were still based on the DNA/cellular/genetic structure Some were cold-blooded, some warm-blooded, some had scales, some had feathers, some had leaves and bark. Millions of species continued adapting, splitting from each other based on circumstance, mutation, adaptation, extinction, until the moment we now arrive at.

Eventually, life conquered the earth.

  1. It’s the process where organisms, in a species, become more adapted to their environment through genetic changes.

  2. It is driven by Natural Selection:
    a) Natural selection is the reproductively positive/negative selection of organisms who have, generically determined, beneficial/ill-adapted traits.

  3. Genetic recombination, mutations, and diversity all play a role in keeping:
    a) the gene pool fresh bubbling
    b) individual organisms ready to adapt to new environments.

I only have these three main points, jeez, I wish I had something else to throw at ya.

Oh yes, a small addition…

Apparently evolution doesn’t even require organisms to work. It only needs things which exhibit heredity and a changing environment to drive selection.

  1. Offspring are mostly a (comingled) copy of their parent(s)'s attributes

  2. But there are occasional very small changes.

  3. Some changes increase or decrease an organism’s ability to reproduce or survive to reproduce in a given environment.

  4. By (1), (2), and (3), changes which increase an organisms ability to reproduce in a given environment tend to be represented in more and more members of the species over time. Changes which decrease an organisms ability to reproduce tend die out (but may recur as mutation again). The speed by which an attribute takes over or dies out depends on how much it alters reproductive odds.

  5. Environments are different, and they sometimes change.

  6. By (4) and (5), organisms (even of the same species) that develop in different conditions will carry different attributes.

  7. Generally, organisms can interbreed with organisms with similar attributes. This is a common (but not the only) definition of “species.”

  8. But there are attributes which are incompatible with interbreeding.

  9. By (6), (7), and (8), organisms which develop in different conditions over a sufficient period of time to develop breeding incompatibilities are commonly considered to have become separate species.

  10. Trivial (CS-101 homework level) computer simulations of this process demonstrate that even very small increased/decreased reproductive success rates of a mutation will either die out or come to dominate a population in a much shorter time than most people realize (a few thousand generations is more than enough).

  11. No crocoducks are harmed in this process. No “goal” exists for the process beyond better adaptation to the environment of the moment. Nothing is ever in a “half form.”

  12. Demonstration of an irreproducably complex attribute which could not have evolved in a small number of coincident mutations would be a devastating argument against evolutionary theory. But
    12a. There haven’t been any found yet, and the theory of course predicts none will be.
    12b. It wouldn’t make Creationism or Intelligent Design correct even if there were
    12c. Opponents of evolution aren’t listening when people tell them that they have to come up with something more than just the ear or the eye, which have been shown not only not to be irreproducably complex, but that each stage of the evolution of these organs is still present in modern nature.

  13. Standard evolutionary/natural selection processes can apply to non-living things, so long as reproduction and selection are present, and there’s nothing special about “living” things besides their life.

  14. Certain relatively simple chemical compounds are cable of self reproduction (in the simplest cases, merely by growing too large and breaking).

  15. There were (and are) a lot of random chemical compounds floating around in the primordial and current ecosystems.

  16. (13), (14), and (15) give a plausible explanation for abiogenesis (the transition from lifelessness to life). Most other proposed non-scientific theories fail the induction principle (they require spontaneous generation of a complex system in order to explain the spontaneous generation of complex systems), and hence are obviously invalid from a logical standpoint.

  17. A significant percentage of the people on earth believe in the non-scientific explanation anyway.

  18. The number of people who believe in a fact has no bearing on its truth or falsehood.

Well I think of evolution as saying if you wait long enough all combinations of atoms will happen thus there is no creator or plan. Some of these become alive, somehow, and reproduce right away, somehow.

I don’t believe much of it because if I go for a walk in the woods and see a squirrel atop a junk TV set I’d have to believe they BOTH just randomly formed there then, they are so adamant there is no maker of anything. When I believe the 1957 Chevy cars just spontaneously formed in 1957, then I will believe the squirrel in the park did as well. I actually have less problem with that occasionally something could randomly form, but that it is alive and that it just happened to be able to reproduce, now there is the problem.

The other problem is it fails to explain LIFE or why scientists cannot give life to something. They know every element in a cell yet cannot build a living one, why? They could even make it larger so easier to work with, but they seem to make not a thing alive while claiming it just formed randomly in a pond. Well, then go make us some of those. I notice all evolutionists never talk about why they cannot create life, and it is supposed to be easy once you set up the right materials. If they cannot even BEGIN their process, why would I want to believe the rest of it?

First off, evolution doesn’t deal with the origin of life, only with how it changes over time.

Charles Darwin published On the Origin of Species by Means of Natural Selection 150 years ago after years of study and thought. The basic idea is that changes in living things are passed down to descendants, and that changes increasing an organism’s chances of survival and reproduction are more likely to be passed down than changes that don’t.

Gregor Medel’s work on heredity showed how these changes are passed down from generation to generation. The later discovery of DNA showed the precise conduit for the changes. The genes contained within DNA can mutate. Even though most mutations result in changes that are selected against, some produce a benefit. Some mutations are neither beneficial or harmful, and are still passed down to descendants. Still other mutations are harmful, but survive through enough generations to be altered further into a beneficial mutation.
The ingenuity of the process is astounding and fascinating.

Initially this process was thought to take place gradually or long stretches of time. However, a newer theory called “punctuated equilibrium” suggests long stretches of little or no change in species interrupted by shorter (but still long by human standards) periods of great change. These upheavals usually coincide with changes in the environment ranging from meteor impacts and extinction events to bodies of water and land masses becoming isolated.

Every time new information is discovered relating to life, the theory of evolution has been validated. I can’t think of a time when the result of a test hasn’t been predicted to some degree by what evolution would expect. Like any other part of science, evolution is subject to alterations based on future research, and we don’t know everything and we never will.

Yes I will also agree many things can change over time and that they had to be so designed to be able to live on a planet with seasons of the year, and the much longer solar seasons that bring ice ages and such. I believe in the big bang, and the 14 billion years and all that, in fact nothing in scripture says otherwise.

I still remember the 1950’s going to the university where an evolutionist blasted how silly and stupid was the idea everything started all at once in a big burst of light and then gasses and water and such with no form and void formed what we have now, complete silliness. He then told us about the real answer, the steady state theory. Everything just always was. Well that covers it, and he said no need to look any further. I wonder what he would say today about the big bang, which sounds an awful lot like scripture?

But the forming of life DOES form the basis for the theory of evolution today, it cannot be left out unless you stick in a creator and they SURE are not going to do that. So, let them build a living cell and they can use any elements in the whole table, make it any size, but they must be able to put life in it without bringing life from something else to it. It must feed, grow, expel wastes, reproduce, and do everything a simple cell does. Till they do the whole theory is unproven.

I do agree with post 3 that changes can happen as generations go by, but who says it is random, it may be programmed into genetics to change this way or that if it gets cooler or dryer for instance, I doubt many changes are mutations at all, maybe a very few. But build me stuff that is alive first, out of just the elements on earth, then we can talk further about the rest of the theory.

I also don’t believe in anything scientists can’t build in a lab. As far as I know there is no sun. I’m not so sure about gravity either. They can “demonstrate” it, but they can’t “create” it. I’m pretty good with light, though. Even back in the early times they could make light using fire (except during the Great Flood when things were kinda soggy for a while). I get most of my science news from Fox because they use shorter words than shows like Nova on PBS.

Evolution is the necessary outcome of information copying itself imperfectly, but nevertheless with high fidelity, at a rate depending on external factors providing finite resources for copy-creation.

OK – going by the rules and having read nothing but the OP:

In a real nutshell…

  1. Random mutations.
  2. Natural Selection (“survival of the fittest.”)
  3. LOTS of time for stuff to happen.

Really, that’s pretty much all there is to it – all the rest is, in a sense, commentary. E.g., I know some or a lot about Punctuated Equilibrium, Gene Diversity, Isolated Populations and why they change, Genetic Similarity, why we aren’t “descended” from chimps, or even from monkeys… etc… But in the end it pretty much boils down to the three points above.

I’ve included “time” in the basic points, because a lot of otherwise intelligent and open minded people just can’t wrap their minds around just how much change can accumulate over time, in tiny, invisible increments.