Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Stupid Question about Genes

  1. Jul 16, 2012 #1
    Years ago (I'm talking 20 years or so) I saw something on TV about the human genome project. The narrator was Asian so it might have been Michio Kaku. Anyway, I recall him having said that humans have all the genetic instructions needed to make all the other animals, while none of the other animals have all the instructions needed for a human.

    I took this to mean that you could sort through a human's genes and find all the instructions you needed to make an elephant or lizard or eagle.

    It seemed plausible at the time, but now I wonder the extent to which I misheard or misinterpreted it, because it strikes me as beyond far fetched to think I have elephant instructions in me.
  2. jcsd
  3. Jul 16, 2012 #2


    User Avatar

    Staff: Mentor

    That's off. We do share many genes, but not all.

    If you take a look at the phylogenetic tree, at some point we (humans) had a common ancestor with elephant - so both branches started with identical set of genes. In a way we can say these are common. But - all new genes that appeared after the moment of the split are not common (so we have genes that are not present in elephants and elephants have genes that we don't have), and many (if not all) of the earlier genes mutated, so while they are similar, they are not identical.

    This is just applying a common reason, I am sure there is more to it.
  4. Jul 16, 2012 #3
    Thanks. This makes sense.
  5. Jul 17, 2012 #4
    The last common ancestor of humans and elephants is the last common ancestor of all mammals. An astonishing amount is known about this species – it most closely resembles a modern rodent. In any case, the idea that there is some unequal split between the human genome and that of other species is not accurate, but it is absolutely true that the genomes of extremely diverse species are similar to a very surprising degree. The morphology of a fruit fly is built by essentially the same genes that build the morphology of a human. I can anticipate that some of the experts who post on this thread might be choking on their coffee reading that. It’s an assertion that requires a lot of qualification. There are, for example, a group of genes in the human genome called BMP because the proteins they make are ‘bone morphetic proteins’. Clearly, fruit flies don’t have bones and therefore don’t have any of that particular group. But the segmentation of the fruit fly’s body is controlled by hox genes as is the segmentation of the human body (which actually goes way beyond the segmentation of our spines). There is a gene called PAX6 a certain allele of which will cause a fruit fly to be born without any eyes. The same allele in a human being causes them to be born without any pupils in their eye. These generic elements between the two genomes are extraordinarily extensive, that is the point. And again, the key thing to understand is that it is not the content of the gene that controls morphology, it is the sequence in which they are expressed that controls the morphology. Another assertion I might make that might not be approved of is to suggest that actually, it is not so much the morphology of a species that evolves, that is really just a secondary consequence. What evolves, it seems to me, is the embryonic developmental sequence, and the generic features of that sequence between species as diverse as humans and fruit flies is quite striking. The changes in the sequence that bring about two such diverse morphologies are much more subtle than might be imagined.
  6. Jul 17, 2012 #5
    Thanks, Ken. Very interesting.

    I had the idea if there were anything to it it would lie in sharing genes for really basic things, like proteins, at the level well before they start adding up to one specific creature or another.
  7. Jul 18, 2012 #6
    All mammals have seven vertebrae in the neck, mouse to giraffe.
  8. Jul 20, 2012 #7
    This can not be true. Both humans and elephants are placental mammals (i.e., eutharia). Neither monotremes nor marsupials are descended from the last common ancestors of all placental mammals. Thus, the platypus and the kangaroo could not be descended from this common ancestor of humans and elephants.
    As far as looking like a rodent: It depends on which rodent.
    To get a better idea of what this common ancestor looked like, I reviewed:
    "The Ancestors Tale" by Richard Dawkins (Mariner Books, 2004).
    Dawkins claims that the Afrotheria were the "last placental mammals to join are pilgrimage". This means that the common ancestor of the Afrotheria is the ancestor of all the placental mammals. The Afrotheria lineage includes both elephants and human beings.
    The Afrotheria split off from the other placental mammals about 105 million years ago. The rodents split off from nonAfrothere mammals about 75 million years ago (page 179). The rodent lineage does not contain elephants. Therefore, rodents are closer related to us than elephants. Rodents don't look anything like elephants, manatees or other Afrotheria. Therefore, I don't think that one could comfortably say that the common ancestor of elephants and humans resembled rodents more than elephants.
    If one has to make an analogy between the common ancestor of all placental mammals and an extant mammal, then let it be the elephant shrew. The elephant shrew superficially looks like a rodent, anyway. It happens to have a long nose like an elephant, but it has generalized teeth roughly like a rodent.
    No one knows yet whether the long nose of the elephant shrew is homologous to the trunk of the elephant. However, no one has proven that the long nose is merely analogous to the trunk of an elephant. The generalized teeth resemble (vaguely) those of a human more than those of an elephant.
    Now, one doesn't have to insist that a common ancestor "look like" any extant species. However, making such comparisons helps wrap ones mind around the concept of evolution. Therefore, I propose the following. The common ancestor of elephants and humans looked vaguely like an elephant shrew.
    Cute little fellas, too!
    Last edited: Jul 20, 2012
  9. Jul 20, 2012 #8
    Fascinating stuff Darwin123, and believe me I bow to your clearly superior knowledge. I don’t offer the following as a challenge to what you say, only as a defence / explanation of the logic that underpinned my assertions. It comes from something I took from another forum I used to engage with, something posted by someone very knowledgeable, which I found fascinating and deeply insightful at the time.

    Before I recount that, firstly there is one strong piece of evidence that I encountered elsewhere. Apparently, there are extant on earth today a little above 4000 mammalian species. More than 50% of them are species of rodent. More than 50% of the remainder are species of bat. That means that only one thousand or so cover all other mammals, including all of the mammalian mega fauna like buffalo, big cats, ape and simian species and so on. The fact that there are only 4000 or so mammalian species in all is an indication of their relatively recent appearance. (The first mammal species were contemporary with dinosaurs. They were sufficiently small that they did not compete with and did not tend to come to the attention of dinosaur species, hence their ability to survive in a world dominated by large scale reptiles.) In any case, what I am suggesting is that the predominance of rodent species and bat species (called flying mouse in German) does suggest that those species have been around the longest.

    Whatever the case about that the other evidence I refer to was an article in Scientific American about a paleontological discovery that provided evidence about the earliest mammalian species. Unfortunately, the article was referenced through another article and the first article is now so old that you have to be a paying subscriber to access it. All I can provide is a link to the first article that referenced the actual article I am talking about.


    In any case, it described the earliest mammalian species as a small creature with short legs that moved very close to the ground. It had no ears to pick up airborne vibration, but it used its lower jaw to detect ground based vibration. Over time, little pieces of the lower jaw broke away to form the bones of the inner ear that today, remain one of the morphological features common to and unique to all mammalian species.
  10. Jul 23, 2012 #9
    The number of species increases with time. However, the rate of speciation may be different. Some clades may be more "evolvable" than others.
    Bats may be far more evolvable than most of the other mammals because they fly. Flight can spread animals far and wide into different environments. By forcing the individuals to face different types of "challenges", flight could increase the rate of speciation. Animals with flight may have a bigger rate of speciation than animals that don't fly. Thus, the bat doesn't necessarily have to be one of the oldest species.

    This doesn't necessarily sound like rodents. Rodents have ears, including the stapes. However, the hypothesized ancestor here doesn't have true ears. It also has a more complex jaw than a rodent. Or for that matter, it is also different from an elephant shrew.
    There are no extant species of mammal which doesn't have the three stapes of the middle ear. There are fossils of mammals that have ears that seem "intermediate" in the sense that the jaw bones have started to migrate. True stapes haven't formed yet, but some jaws have moved in the right direction. These aren't rodents, per se.
  11. Jul 27, 2012 #10
    That's incorrect. We don't share the same DNA as other species.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook