When I was a child I remember hearing humans came from monkeys. I asked myself, "Then why are monkeys still around?" A valid question. The problem with the initial statement though is that we did not come from monkeys, but rather we share a common ancestor. When it comes to common ancestors and evolution, genetic sequencing has provided a great understanding.
I'm sure you've heard it before; humans and chimpanzees are about 98.8% similar. What does that really mean though? This number refers to comparing single nucleotide changes in the DNA, or changes in the sequence of the A,C,G,T code.
Comparing genetic duplications in genes, the number lowers to 96%. What's a duplication? As Even Eichler of University of Washington says, if we consider the genetic code as a book, entire pages will be repeated in one species but not the other. So conservatively, we are 96% alike with out closest cousin. Here's some other common animals and our genetic similarites (these numbers are consistent across all reliable sources):
Fruit Fly: 60%
Interesting to look at. What I find most fascinating is the 50% match to bananas! Animal and plant life share so much ancient DNA coding from way back when plant and animal life diverged approximately 1.5 billion years ago.
The sequencing technology allowing for genetic comparison has been huge for anthropologists and evolutionary biologists. Anthropologists have used comparisons of genes between humans and our closest cousins to better understand when and how genetic variations occurred. Evolution was already well established before this technology existed with fossil records, embryology, comparisons of skeletal systems, study of vestigal appendages, and finally the understanding of the driver of evolution: natural selection. Genetic sequencing confirmed our understanding of species divergence and evolution, and also allowed scientists to better understand and build the the fascinating "tree of life."