The Common Ancestry Thread

by cantleave 271 Replies latest members adult

  • cantleave


    How many times have you heard things like “If we evolved from Chimps – why are there still chimps?” or “My ancestors were not Neanderthals”? These are common objections vomited out by creationists who believe that individual species or kinds (whatever the hell that means) where created individually by an intelligent designer. This is in direct conflict with the evolutionary principle of common descent. What both these objections demonstrate is that the person making these statements does not in fact understand what common descent is, or has not looked the evidence that actually backs it up.

    I am not trying to be disparaging to creationists because when I was a JW I dismissed common descent and biological evolution because it went against my belief system. I couldn’t believe that my mother, who was a nurse and friends, many of whom were very intelligent, thoughtful and sincere people, would reject this theory if it had any credence. When I researched subject I did look outside the Watchtower publications, but focussed on creationist books and websites, falling into the trap of confirmation bias. It can be really gut-wrenching to know that along held assertion is wrong, and it is easier to read materials that support your point of view.

    For a theory to be held to scrutiny the evidence supporting it needs to be falsifiable. What does that mean? It means the theory needs to have the potential for some observation to demonstrate that the theory is false. For example if in the fossil record, the clichéd fossilised rabbit being found Cambrian rocks, would completely destroy the theory as we understand today.

    So what do we mean by common descent? An evolutionary biologist will describe common descent as group of organisms that have a common ancestor. But in reality it goes further than that, in that all living organisms on Earth descended from a common ancestor that lived just under 4 billion years ago. This is not a belief, it does not require blind faith, it is a theory accepted by virtually all biologists because of insurmountable, falsifiable evidence. The purpose of this thread is to show using genetic and chromosomal evidence that common descent of species is a fact beyond reasonable doubt.

    I am going to start with the evidence presented by Endogenous Retroviruses (ERVs)

    What is a retrovirus?

    The most commonly known retrovirus is HIV. But not all such viruses are quite as good at killing their hosts as HIV. R etroviruses also know as RNA viruses have their genes encoded in RNA instead of DNA. Like all viruses once they invade a host organism they need to make copies of themselves. Retroviruses need to use the cellular machinery of the organisms they infect to do this. In order to make itself compatible with the host cell (which is encoded in DNA) the retrovirus RNA needs to be reverse-transcribed into DNA. The virus uses an enzyme called reverse-transcriptase to transform their single-stranded RNA into double-stranded DNA so that it can be integrated into the genome of the cells it has infected. Once the DNA version of the retroviral genes have been incorporated into a cell's genome, the cell copies those genes as part of its normal replication process. Thus, the cell does the work of the virus for it.

    Endogenous retroviruses (ERVs) are remnant genetic sequences where a retrovirus infected the germ cells (cells that gives rise to the gametes) of an ancestor of a mammals or other vertebrate. These genetic sequences are passed on to the next generation and now remain in the genome as genetic detritus.

    More to follow.........

  • bohm

    A slight nitpick, less you attract some of the more slippery elements who love these obfuscations, you should properly rephrase: " An evolutionary biologist will describe common descent as group of organisms that have a common ancestor. But in reality it goes further than that, in that all living organisms on Earth descended from a common ancestor that lived just under 4 billion years ago" slightly, since the very early ancestry of life might be better described as a small community or organisms; we do not know, AFAIK.

    Anyway, nit picked.

  • PSacramento

    If we go back far enough, ALL life has a common ancestor since ALL life on this planet is FROM this planet ( unless one believes in the alien life theory).

  • cantleave

    Before I start talking about how ERV’s are proof of common descent I want to nip in the bud the argument that these bits of genetic detritus are actually purposeful bits a design, put there by god to help us defend us against viral or bacterial attack. That they are not remnants of viral genomes.

    Retroviruses are a very large and diverse group of organisms. They cannot be lumped together any more than mammals can be lumped together and called cows.

    There are currently seven types of retroviruses, with their own defining genes, structure, and preferred desired host cells. The only similarity between these groups is their need for the genes of their hosts cells. Their infecting a host cell may result results in their genes hanging out in our DNA as endogenous retroviruses.

    Our knowledge of these organisms allows us to identify what group the ERV in question used to belong to. We can trace how that ERV mutated differentially in different species of primates, or notice it is only found in humans, or that its only found in chickens. We can also know the ERV in question isn’t coding for HIV-1. So please don’t go to answers in genesis and spout the pseudoscience you find on there trying to convince the uneducated that what has been found on Human and chimp DNA are not ERVs.

  • cantleave

    Bohm, please nitpick away, I value your input, I am not an expert in ERVs they were just a major convincer for me.

  • cantleave

    Why are we discussing ERV's? Well first of all, becuase they provide absolute conclusive proof that Chimpanzees and Human beings share a common ancestor.

    Genetic studies have shown that Humans and Chimpanzees share 16 K-Class ERVs.

    The only way this could happen is if there is a common ancestor. I repeat Humans share 16 K-Class ERVs with chimpanzees.

    The probability that a virus infected a human and a chimpanzee in the EXACT same location 16 times in a row is, 1 in 2 x 10 to the power of 138.

    I can not think of analogy strong enogh to describe those odds so I will steal one...

    This is the roughly equivalent to the "chance that you have of being struck by lightning after just winning the Power ball, Pick 3, and Pick 4 lotteries while simultaneously throwing snake-eyes at craps, being dealt a 2-card blackjack, winning on black 13 in roulette, AND being dealt a royal flush in poker with no draws, all THREE TIMES IN A ROW,"

  • cantleave

    ERV evidence doesn't stop there..

    135 different vertebrates were sequenced for ERVs and the distribution of ERVs matches the hierarchical distribution expected but the evolutionary process.

    The 135 vertebrates sequenced include reptiles, birds and mammals.

    The fact that ERVs are inherited, they're shared between multiple species, and the improbability of a virus transcribing its RNA in the EXACT SAME location of the genome of different animals leads us to conclude that pretty much the only way multiple animals could have obtained those unique sequences in the DNA is if it shares a common ancestor.

    The existence of common ancestors for multiple species of animals confirms that macro-evolution occurs.

  • EntirelyPossible

    I would add fused human chromosome 2. We have 23 pairs, chimp and other distantly related apes have 24. Our human chromosome 2 shows evidence of being two chromosomes that fused into one at some point in the past after our lineage split from other great apes. It has a vestigial telomere in the middle (typically the endcap of a chromosome) for a total of 3, one on each end and 1 in the middle. It also has an additional centomere (total of 2) where all other human and great ape chromosomes have 1.

    I am sure someone like bohm will get nickpicky () and correct what I said that wasn't quite correct there. I look forward to that.

  • cofty

    Love it - marking for later

  • cantleave

    Another convincing genetic evidence is provided by Redundant Pseudogenes.

    So what is a pseudogene?

    Pseudogenes are genes present in an organism's genome that have lost the ability to transcribe for proteins due to mutation. They are therefore vestigial components of the genome, part of the genetic sequence but possessing no functionality. They are evolutionary carry overs from our ancestors.

    Interestingly in our genome there are around 19,000 of these redundant pseudogenes, almost as many as the number of functional coding genes. One example of a redundant pseudogene is the gene that produces L-gulonolactone oxidase, the enzyme used to synthesize vitamin C. Research shows that this gene was inactivated in the common ancestor of all simians so even our JWN friend Shamus100 lacks the ability to make vitamin C.

    These redundant genetic sequences are in a wide range of organisms (yes Shelby crossing various Genera from bacteria to reptiles and amphibians to humans).

    So what makes pseudogenes interesting to the evolutionary biologist? (quick rant – I f*cking hate the term evolutionist, anyone from any profession can educate themselves on evolutionary theory, those that study it are called evolutionary biologists, neither is an “evolutionist"!!!!!)

    Well, for one thing, the formation of pseudogenes is controlled by random processes, whether by retropositioning or duplication. So there’s no good reason why two completely different organisms would have the same pseudogenes in the same genomic locations… other than common heredity. In addition Because of the fact that pseudogenes are largely non-functional, they pick up mutations at about the same rate as other non-coding DNA . To clarify that statement, a mutation in a non-coding region is far more likely to passed onto offspring because a mutation has no effect on the organism that gets it. A mutation in a gene is more likely to be bad thing than beneficial (although the majority are neutral). So over time (many generations) there are more differences in non coding regions of DNA between individuals, than the functional genes. This why DNA fingerprinting looks at differences in non coding regions between people to find unique profiles.

    The acquisition of individual mutations is itself a random process, so there would be even less reason for different organisms to have identical pseudogenes in the same locations with the same mutations… other than common heredity. This means specific pseudogenes are often compared across species to ascertain evolutionary relationships.

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