Your Inner Fish

Though we often hear that all living things are somehow related, this documentary showed how many resulting similarities we have to other organisms. For example, the structure of the bones in our limbs matches that of birds, and even, yes, fish.
But that’s not where the similarities end. Human and fish embryos share early forms of gills, the same overall cells, and undescended gonads. But with all these similarities between species, it can be hard to imagine how our differences evolved. This documentary recounted the search for the first organisms to transfer from living underwater to living on land. Eventually, they it revealed Tiktaalik, a transitional flat-headed fish. Like fish, it had scales, fins and gills, but like mammals, it had a neck and lungs. It even matched the skeletal pattern of our limbs today. Other transitional organisms, like the animals between reptiles and mammals, would also share characteristics of both groups of organisms. An animal linking reptiles to mammals might have fur for insulation, but also be cold-blooded. In addition, it may have given live birth. Like both reptiles and mammals, it would have had a backbone. Here’s a drawing of one possible transitional animal:  


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