Question: u know ho r 180 millions great grandfather was a fish, how do we know this did someone find a fossil and find similler dna to homosapians

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  1. We can follow evolution in a couple of ways. First we have a fossil record that follows back a very long way. The fossil record is all of the bones from creatures in our past. Before humans there was something that gave rise to both humans and chimps, before that there was something else and something else. The point is that each time there are subtle changes we can observe that prove slow adaptations over time.
    My expertise is in the DNA evidence though. If you look at human DNA and compare it to any other animal you can find similarities. The more similarities the closer we are related and consequently the less time from a common ancestor. We do have a common ancestor with fish and you can see it in the sequence of our DNA hen compared to fish and even more amazing then that you can trace similarities all the way back to microbial life.
    With biology as with most science there is rarely a single path to an answer but many approaches that produce a coherent picture. The evidence that has been collected from a number of sources makes it very clear that we definitely have common ancestory with fish.


  2. Hi Drunktinyturtle

    James has given you a great answer; I might just come at it from a different angle.

    The DNA that you and I and all humans have is much similar to one another than our DNA is to say a frog. When we compare our DNA to a lizard, it is more similar than it is to a frog. So we find that genetically we are more similar to some animals than others.

    But we can also look at our anatomy. You and I are much more similar to a horse in terms of our anatomy than we are to a bird in very important ways. All birds have feathers and all mammals have a type of hair. So we can go through all the features and match them up to other animals.

    When we start matching up all these features, we find that, again, we are closer related to some animals than others. The features that we share with other animals we conclude have come from a common ancestor. For example, when we look around at all land animals, we find they all have four limbs, generally with 5 digits on each limb. So we conclude that the common ancestor of everything must have had these same features.

    So if we start winding the clock backwards, we should expect there to be a point in time where there are no land animals, but something with 4 limbs that has features similar to all land animals, such as lungs, the vertebrate eye and so on.

    Such a creature was predicted to exist for a long time, but the furthest animals back were amphibian like creatures. They breathed air, had reasonably well developed limbs, but likely lived in aquatic environments. Beyond them were fish, that did have four limbs but and breathed air (like the Australian lung fish), but were missing other vital features. Then in 2004, Tiktaalik was discovered.

    Tiktaalik is a mixture between a fish and a tetrapod, those early amphibians. It appears that it breathed air, had long limbs, but importantly had some fish features, and tetrapod (land animal) features. It was the transitional species between the water and the land.

    It is a fascinating story