Most explanations of Darwinian evolution refer to genetic material as the manner in which changes are passed down to one's descendants. Now, a study by Jiali Li of the Scripps Institute in Florida finds that prions, the proteins that cause diseases like mad cow disease evolve in response to their environment. Prions have no genes, no chromosomes, and no DNA or RNA at all!
Scientists are not ready to classify prions as living things, even though this discovery may lead to some refinements in the definition of life. Link
Prions are rogue version of a protein called PrP. Like all proteins, they are made up of chains of amino acids that fold into a complex three-dimensional structure. Prions are versions of PrP that have folded incorrectly and this misfolded form, called PrPSc, is social, evangelical and murderous. It converts normal prion proteins into a likeness of its abnormal self, and it rapidly gathers together in large clumps that damage and kill surrounding tissues.
Li has found that variation can creep into populations of initially identical prions. Their amino acid sequence stays the same but their already abnormal structures become increasingly twisted. These "mutant" forms have varying degrees of success in different environments. Some do well in brain tissue; others thrive in other types of cell. In each case, natural selection culls the least successful ones. The survivors pass on their structure to the "next generation", by altering the folds of normal prion proteins.
Scientists are not ready to classify prions as living things, even though this discovery may lead to some refinements in the definition of life. Link
As these things live in a world where reproduction is not guaranteed, over time, changes will either help the population of things get larger as they reproduce better, lessen the population as the things reproduce poorly, or have no effect as the reproductive rate doesn't change.
Now, as things live in a world with finite resources and things eat other things, over time, a population of things will either die out, stay the same size or increase.
Noting this, it stands to reason that in most cases, evolutionary changes that hinder an individual's ability to reproduce, will die out in a population of things unless that change reoccurs often enough.
This means that successful mutations promote themselves by default, because unsuccessful ones die out through the lower reproductive potential they impart onto their owners. What survives are the individuals with changes that do not affect their "reproductive potential". But what thrives (over time) in the population are the changes that help the critters reproduce better.
It's a remarkably simple concept that plays out amazingly over generations in population biology and also maps over into other disciplines.
Happy New Year.
Prions can not exist without genes.
To say a prion does not have DNA or genes is exactly the same as saying a brick does not have a house. It makes no sense.