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Of all the species that have existed on Earth 99 percent have gone extinct and even fewer make it into the fossil record and a very small fraction of those that fossil are actually found even partially complete. Even if all of them did fossil many would be too hard dig for many of them. And also it is highly unlikely that most would be found complete, due to the number of natural disasters and processes that have happened from the animal’s death to whenever it is discovered.
Natural starters such as mudslides, floods, earthquakes, and the shifting of the earth’s tectonic would have destroyed traces of many species so either we find fragments or nothing at all. Humans and fish are alike, but not necessarily externally. We both have similar bones, the same number of limbs, and we both have essentially the same organs (but each on has a slightly different purpose). Although we have hands with fingers, fish have the same bones but in different sizes and they are used for different reasons.
And when observed closely using the fossils record we realize that our hands and fingers are nothing more than advanced fins that can enable us to swim as well as grasp things. Each cell in the human body contains the same DNA, but they are used differently to generate different body parts and such. If each cell was to contain different sets of DNA we would be an uncoordinated Jumble of parts with no real purpose or connection within ourselves. We would Just be a separate pile of body parts. Teeth in fact did not evolve as a reaction to predators as defense.
They evolved because food was becoming more complex and not something that they could suck up and digest simply by having them go straight into the stomach. More complex algae and seaweed evolved and the “herbivores” needed to break these down and get these into their mouths and these algae would take too long to digest in the stomach and couldn’t simply be taken by vacuum. Predators also needed a way to break down the newly developed herbivores and so they gained teeth that could tear he herbivores into smaller parts so they could be taken in better.
Teeth were a response to food that was complex and not eatable through vacuum. Even so teeth may have evolved for predators to bite through the armor that herbivores developed. As stated in the book regardless of what creature it is, all creatures go through the same stages in the germ layer. They develop the same parts while in the germ layer. The germ layer has the same basic blueprint for all creatures. Evolution of Species By Sash-Summary