The sequencing of the human genome has been compared to the seven wonders of the ancient world and man landing on the moon; yet understanding our own genome gives us only a minor glimpse into what makes us human. Every creature on earth has its own genome, and the similarities and differences in that is what makes us human. The most important species for those comparisons are mammals because they are similar enough to us to help us pinpoint the parts of the genome that may be most important.
There are about 3,200,000 base pairs in the human genome. Among humans the variations in this genome is anywhere from thousands of base pairs to a few million. This has led to the ideas that humans are 99.9 percent similar, which is generally true. Most mammal species have base pairs which are similar in number though they do have some variation.
The animal we think of as being closest to us are chimpanzees, which are about 98.7 percent similar in DNA sequence to humans. This is an important point because it helps us to understand how little the genome has to change in order to have huge impacts on a species. In addition to this, Chimpanzees, gorillas and orangutans all have one more chromosome than humans.
What is far stranger than having such similarities with the chimpanzee is that humans also have very large genetic similarities with the mouse. In fact, according to a 2002 draft sequence of the mouse, humans share about 99 percent of the same genes. One of the interesting points to learn from this study is the the “junk” DNA. This is because this DNA, which previously was assumed to do little or nothing, is also similar. This seems to imply that this may have far more importance than was previously assumed.
Another of the touchstone animals for any type of study of this type is the pig. Considered similar in many ways to humans, they share about 83 percent of the same genome sequences as humans. This is considerably less than the others, but still very high compared to an animal outside of the mammalian family.
The decoding of the human genome is one of the great human accomplishments, but without anything to compare it to, all you have is a long list of base pairs. Comparing the genome of different humans is worthwhile, but with the difference often being so small, the answers you get are generally very specific. By comparing human genomes with those of other mammals, though, one can get a better idea of the specific sequences that make humans human.