Homology supported by genetics?

28


Discussion by: kaloskm

I except evolution but i like to get my facts straight. 

I got in to a discussion with a creationist a few days ago about homology being explainable by common ancestory. I was reffered to an article by a Kofahl, Robert E from 1992 called "A serious problem for homology" basically claiming that this is wrong. I have since been searching the internet for some information on the subject, however im getting very different opinions, and frankly I don't know what to think. 

I was under the empression that homology by now was well supported by genetics. 

Anyone here able to help me out?

 

28 COMMENTS

  1. Homologous features are those which are derived from a common ancestor. Traits which seem homologous can sometimes appear by convergence. I don’t think any of this is controversial. From the way you put your question I’m inclined to wonder about your motives; whether you are asking out of curiosity and a desire for knowledge, or perhaps one of those ‘hit and run’ creationist types who ask a question hoping to get the atheists in an anxious flurry, and then do not participate further in the discussion. I hope the former; if I misjudge you, forgive me brother.

  2. Quoting the Wikipedia:
    In the context of biology, homology simply defines a relationship between a pair of structures, or genes, due to having shared ancestry. A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates. Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.

    • In reply to #5 by Roedy:

      I do not think you are serious. You have never posted anything other than this creationist bit of crab bait.

      If you presented this without the dishonest cover story, I would be willing to engage.

      • What has the dishonest cover story, as you see it, got to do with engaging? It’s illogical that that should be the criterion you use for deciding whether an idea is worthwhile or not. Inferring people’s sincerity from this sort of correspondence seems to me a really impossible and, therefore, time-wasting exercise. In reply to #15 by Roedy:

        In reply to #5 by Roedy:

        I do not think you are serious. You have never posted anything other than this creationist bit of crab bait.

        If you presented this without the dishonest cover story, I would be willing to engage.

  3. Hi Kaloskm,

    I don’t particularly care if you are a creationist or not. Common features are how before genetics animals were largely classified so the fact that so many animals share much the same body plan from a certain point. That is body plans have changed from time to time e.g. fish to and land animals have different body plans. If we came from fish then we should be able to show structures that both have in common. What is more if amphibians evolved from fish and reptiles evolved from ancient amphibians we should see features that evolved in ancient amphibians carried forward to reptiles but not backwards to fish. Vestigial features like the coccyx in humans is a good example of a feature we share with our common ancestors in this case the common ancestor of monkeys and humans. There are many others.

    Now it is possible to have similar features evolved independently such as eyes. In the case of eyes the modern features also show homology for example squid have an eye that evolved independently to the eyes that we have in humans the rods and cones are back to front you would expect to find therefore other molluscs to have similar eyes and other primates to have similar back to front eyes as humans. This is the case. So through these processes and by looking at the fossil record we have over time created a picture of evolution and the direction it took.

    Genetics allows us to confirm the picture we have that is DNA is preserved with modification so any eye for example that evolved in another animal would not need to evolve in the same part of this chromosome or that it could be nestled between this bit of DNA on one side and another on the other the common ancestor and this placement is likely to be true in cousins eg. apes, monkeys and humans would be expected (if evolution is true) to have their eye genes in much the same location. They do. Squid eye genes will probably look different and may be in a very different location with other genes around either side, other molluscs like octopus would then have their eye genes in the same place surrounded by similar genes. So that is the connection multiple threads of evidence confirming each other.

    Hope this helps

    • In reply to #8 by Reckless Monkey:

      Excellent explanation!

      For those unclear about the definition:

      http://www.biology-online.org/dictionary/Homology

      Homology – Definition

      noun, plural: homologies

      (1) A degree of similarity, as in position or structure, and that may indicate a common origin; a correspondence of structure

      (2) (evolutionary biology) A state of similarity in structure and anatomical position but not necessarily in function between different organisms indicating a common ancestry or evolutionary origin

      (3) (genetics) A condition denoting to the pair of chromosomes having corresponding genes for a particular trait or characteristic

  4. Reckless Monkey nails it. Hey reckless, you saved me a whole lotta typing! The structures raise awesome evidence and then the genes underlying those structures seal the deal (when they are sequenced and the sequences compared)…
    Nice job!

  5. Thank you for your answers. For the record i’m an atheist and i find the idea of creationism silly. And the reason this is my only post is because I only joined this page a few days ago. But maybe i should have been more clear about my motives. Sorry if my question sounded stupid to some of you but i would rather ask a 100 stupid questions than give anyone an answer that i can’t defend.

    • In reply to #11 by kaloskm:

      Thank you for your answers. For the record i’m an atheist and i find the idea of creationism silly. And the reason this is my only post is because I only joined this page a few days ago.

      Welcome!

      Stick around and ask searching questions. It’s the way to learn!
      There are lots of knowledgeable people posting here, so it is only know-it-all creationists who learn nothing from these discussions.

      BTW: – You will have to excuse some posters who are suspicious, having had creationists trying to mislead them by posing as atheists in earlier discussions.

    • Glad you’re not a creationist! It’s not that anyone thinks your question is stupid, just that there have been several ‘I’m an atheist but…’ discussions recently which were clearly not sincere. I hope your question was answered to your satisfaction.

      In reply to #11 by kaloskm:

      Thank you for your answers. For the record i’m an atheist and i find the idea of creationism silly. And the reason this is my only post is because I only joined this page a few days ago. But maybe i should have been more clear about my motives. Sorry if my question sounded stupid to some of you but…

      • Replying to 14
        I don’t understand the obsession with “trolling” which I’ve frequently noted since first posting a few months ago. If an idea is sufficiently interesting or provocative to merit discussion, who cares what the motives are of the person who raises the issue? There are some excellent, very well-informed and lucid atheist/scientific minds who post here and, if there have been insincere contributions, no “creationist” or similar has made any headway at all that I’ve noticed. If the points are dull, obvious or have been much-debated already, why not ignore them or refer the poster to previous threads! I suggest that those are adequate responses to points which don’t merit fresh debate and those which do can be debated entirely irrespective of the motives of the person who raises them. I’m unable to work out what there is to fear from “trolls” who haven’t yet displayed any ability to disrupt RDFRS and, as far as I can see, do more good than harm if they offer worthwhile challenges. In reply to #14 by Archaic Torso:*

        Glad you’re not a creationist! It’s not that anyone thinks your question is stupid, just that there have been several ‘I’m an atheist but…’ discussions recently which were clearly not sincere. I hope your question was answered to your satisfaction.

        In reply to #11 by kaloskm:

        Thank you for your…

  6. Thank you :)

    I’ll watch out for that. This whole idea of questioning evolution is kinda new to me. Until a few months ago when i stumbled on to one of Dawkins’s videos on youtube i had never heard about Creationism/ID. Of course i have heard about God “the creator” but I never imagined that so many people in the western world took it seriously. Just assumed we were long past that. Theres not much talk about this in Denmark. Not yet at least :)

  7. Moderators’ message

    Once again we would remind users not to make derogatory comments about other users of the site.

    If you do not wish to engage with a particular discussion topic, you don’t have to. There are plenty of others to choose from.

    The mods

  8. I seem to have had a comment removed. I don’t remember quite what I wrote but, in view of the Moderators’ explanation whose tenor I entirely support, I apologise unreservedly to whoever I made them to for any derogatory remarks.

    • In reply to #19 by jburnforti:

      I seem to have had a comment removed. I don’t remember quite what I wrote but, in view of the Moderators’ explanation whose tenor I entirely support, I apologise unreservedly to whoever I made them to for any derogatory remarks.

      For clarification, we also remove comments that respond to posts that have been moderated by us. This is partly to remove quotes of comments we’ve removed, and partly to stop threads rolling off-topic.

  9. Ok i think i’m getting the picture. Have done some more reading and i found an example where they had taken the gene that starts the process of building an eye in a mouse and activating it in a fruit fly and the result was not a mouse eye but a fruit fly eye. So if i understand it correctly the development of the eyes of humans and the other apes are homologous because they are so closely related and compared to a much more distant relative the eye development may be analogous. But the genes that starts the process are homologous because they came from the same distant ancestor. And the same goes for looking at for example, arms, front legs and wings as forelimbs from the same ancestor?

    • Yes. The genes that control other genes are referred to as Hox genes (short for homeobox genes). They are extraordinarily conserved across animals. I recommend looking at the animal phyla in the order that they appear in the fossil record and superimposing the genetic account of their history at the same time. If you start with sponges then cnidarians, then all the worms (platyhelminthes and on up), you will see the unmistakable pattern of evolution. From embryonic tissue layers to cleavage patterns, to protostome vs. deuterostome… the genes that underlie these systems and patterns are remarkably similar in vastly different type of organisms

      There is only one explanation that works. Evolution.

      In reply to #21 by kaloskm:

      Ok i think i’m getting the picture. Have done some more reading and i found an example where they had taken the gene that starts the process of building an eye in a mouse and activating it in a fruit fly and the result was not a mouse eye but a fruit fly eye. So if i understand it correctly the deve…

    • In reply to #21 by kaloskm:

      But the genes that starts the process are homologous because they came from the same distant ancestor. And the same goes for looking at for example, arms, front legs and wings as forelimbs from the same ancestor?

      In Vertebrates you can track the development of limbs through fins on sea-floor walking fish,(http://en.wikipedia.org/wiki/Coelacanth) to legs on amphibians, reptiles and mammals, and to wings on birds and bats.

      There is an interesting article on the evolution of hands here:
      http://ngm.nationalgeographic.com/2012/05/hands/zimmer-text

      When Charles Darwin wrote Origin of Species, he singled out this odd coincidence. “What can be more curious,” he asked, “than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern?”

      For Darwin, there was a straightforward answer: We are cousins to bats and to all other animals with hands, and we all inherited our hands from a common ancestor.

  10. The OneZoom Tree of Life ( http://www.onezoom.org ) is a really useful and interesting way to explore the evolutionary relationships between species. They currently have a tree of tetrapods where you can examine lineages of amphibians, mammals and reptiles/birds, and I believe they plan to add fish and other types of organisms too.

    • Hey, just wanted to drop a quick “thank you” on you for this info. Great site!

      In reply to #24 by Archaic Torso:

      The OneZoom Tree of Life ( http://www.onezoom.org ) is a really useful and interesting way to explore the evolutionary relationships between species. They currently have a tree of tetrapods where you can examine lineages of amphibians, mammals and reptiles/birds, and I believe they plan to add fish…

      • No prob!

        In reply to #25 by crookedshoes:

        Hey, just wanted to drop a quick “thank you” on you for this info. Great site!

        In reply to #24 by Archaic Torso:

        The OneZoom Tree of Life ( http://www.onezoom.org ) is a really useful and interesting way to explore the evolutionary relationships between species. They currently have a tree of tetr…

  11. For more detailed discussions of homology and an overview of the classification of all known organisms, I’d recommend ‘The Tree of Life: A Phylogenetic Classification’ by Lecointre & Le Guyander, 2006, Belknap Press of Harvard University Press.

    It’s neither small nor cheap, and is probably a little of of date since classification is such a fast moving field (especially it seems in eubacteria and archaea), but I think it is reasonably authoritative.

  12. Evolutionary actions are derived from quantum waveform frequencies. Evolution is not reversible and probably controlled by gravity as demonstrated by orbiting satellites – time measurement is a derivative of evolution advancement.
    It is a scientific reality that ‘time’ as we know it is variable and that its duration is increased or decreased to match its evolutionary duration. One can then presume that a cosmonaut travelling through space for an extended period would return to earth older and not younger.
    Each and every spices of life is unique with its own evolutionary duration whether it is an individual entity or as a defined mass. Evolution allows for modifications to the various spices as a method of protecting their existence.
    The human life form has evolved through countless modifications over billions of cycles to reach its present state.
    Life forms can be compared with computers. The design of the hardware comparable to the design 0f the life form, the operating software (the soul) of the computer comparable to the initial operational requirement of the life form and a storage devise as way of storing new information.

Leave a Reply