Our still left and right sides are mainly mirror photographs of each other. That can make us bilaterians, a massive team of animals that variety from little flies to big whales. But we and the whales share a considerable difference with flies—where we put our nerve cord. For us, the spinal twine operates down our again. For flies and other bugs, the main nerve twine is on the underside of the animal.
This wouldn’t be that surprising if the two nerve cords had distinct origins, but we’ve discovered that all the molecules that place and pattern the nerve cord are similar in bugs and vertebrates. That implies the nerve cord has often been in the identical location rather, the relaxation of the entire body in some way ended up flipped relative to the nerves. Now, the genome of a odd animal called the acorn worm could help us type out how that could have transpired.
One particular achievable speculation for how the nerve wire flipped is that the ancestor of us vertebrates lived as a burrowing animal in a marine surroundings. There, these kinds of an ancestor might not need any top/bottom axis and could have dropped it. Once its descendants re-emerged from the mud, they re-established this axis but did it in the opposite orientation.