A pseudogene is a gene that has been disabled by mutation, and is no longer functional.

Pseudogene is spelt P-s-e-u-d-o-g-e-n-e and duplicategene is spelt d-u-p-l-i-c-a-t-e-g-e-n-e.

These genes have lost there protein coding abilities and are riddled with deleterious mutations. Two points to the evolutionary theory contribution. By example. Firstly, all great apes have a vitamin C pseudogene that links humans to all other great apes showing common ancestry. Secondly, this gene is inactive in fruitavores ( humans are common ancestors to fruitavores ) as they eat all the vitamin C they need so this gene became invisible to natural selection and deleterious mutation accumulating in the gene were not selected against as the survival and reproductive success of these organisms was no longer affected by not synthesizing vitamin C.

It is clear and obvious than men and ape share common ancestry. The skeletal features alone are sufficient to warrant this as a likely conclusion. But when we compare blood, tissue, and chromosomes, we are inexorably left with the realization our species diverged within the past ten million years, and the fossil evidence also bears this out.

Humans have 23 pairs of chromosomes, whereas most other primates have 24 pairs (I'm not certain about lemurs, lorises, or tarsiers). However, it has been demonstrated that our reduced chromosome count stems from the fusion of a pair of early hominid chromosomes. We see tale-tell signs of the fusion by the presence of telomeres, repeated DNA segments near the ends of chromosomes, where the fusion occurred.

Suppose you created monkeys, and then later created men. Why would you endow each with the same defect? Monkeys and humans both share a pseudogene for expressing a protein that synthesizes ascorbic acid. In each of us the gene does not function, which is why it is called a "pseudogene." Most other species of mammals have a functioning gene, so their diets need not be rich in vitamin C to ensure their good health. We suffer scurvy if we don't get it.

We engineered mice with the human pseudogene in place of their GULO gene. These mice all developed classic symptoms of scurvy when fed diets restricted of ascorbic acid (vitamin C). This proves we correctly identified both the gene and its function.

Separate creations? What possible explanation could there be for designing the same flaw into our respective species? That makes zero sense. However, if we imagine the gene breaking and becoming fixed in an arboreal population rich in vitamin C where the missing gene would go unnoticed, common ancestry explains the presence of the gene in both populations beautifully.

Yet more evidence for common ancestry stems from comparisons of mitochondrial DNA. Mitochondria are organelles within cells that have their own DNA. These are inherited in the egg of the mother, the male sperm does not pass on its own mitochondria. We have grown cows with the mitochondria of rabbits, showing that dramatically unrelated species function just fine with foreign mtDNA (mitochondrial DNA). The mtDNA of chimps and humans is remarkably similar, again indicating our divergence was likely fairly recent in geologic time.