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Theories of Aging
Why we get old
Simple single-celled organisms called prokaryotes, such as bacteria are the earliest forms of life on earth, and still abundant today. Much later evolved the more complex, but still single celled organisms called eukaryotes. From those humble beginnings came the multi-cellular life forms called metazoans. All animal cells, including humans, are eukaryotic cells. Since they share a common origin, they bear a resemblance to each other. Many molecular mechanisms (genes, enzymes, etc.) and biochemical pathways are conserved throughout the evolution towards more complex organisms.
Humans share approximately 98.8% of their genes with chimpanzees. This 1.2% genetic difference is enough to account for the differences between the two species. It may be even more surprising, however, to learn that organisms as far apart as yeast and humans have many genes in common. At least 20% of genes in humans that play a role in causing disease have counterparts in yeast. When scientists spliced over 400 different human genes into the yeast Saccharomyces cerevisiae, they found that a full 47% functionally replaced the yeast’s own genes.
