PZ Myers writes about Random Acts of Evolution in the latest issue of Seed magazine. The subtitle says it all.
The idea of humankind as a paragon of design is called into question by the puffer fish genome—the smallest, tidiest vertebrate genome of all.The genome of the puffer fish (Takifugu rubripes or Fugu rubripes) has about the same number of genes as other vertebrates (20,000) but its genome is only 400 Mb in size [Fugu Genome Project]. This is about 12.5% of the size of mammalian genomes.
Genomes & Junk DNA
Total Junk so far
The Fugu Genome Project was initiated by workers who wanted to sequence a vertebrate genome with as little junk DNA as possible in order to determine which sequences are essential in vertebrate genomes. The small size of the fugu genome suggests that more than 80% of our genome is non-essential junk.
Many of you might recall the results of my Junk DNA Poll from last January. In case you've forgotten the results, I'll post them again. The question was: "How much of our genome could be deleted without having any significant effect on our species?" The question was designed to find out whether Sandwalk readers believed in junk DNA or whether they were being persuaded by some scientists to think that most of our genome was essential. (Modern creationists are also promoting the death of junk DNA.) There was some dispute about the interpretation of the question but most readers took it to be a question about the amount of junk DNA.
Astonishingly, almost half of Sandwalk readers think that we need more than half of our genome to survive. This would be a surprise to a puffer fish.
I began a series of postings in order to explain what our genome actually looks like. So far we've determined that about 2.5% is essential and 53% is junk. Now it's time to finish off this particular theme and have another vote.
PZ points out that most of what we call junk DNA is not controversial. It consists of LINEs and SINES, which are (mostly) defective transposons. The pufferfish genome has a lot less of this kind of junk DNA than we do. This accounts for a good deal of the reduction n genome size that we see in modern pufferfish.
PZ also points out that we need to think differently about evolution ...
In the world of genomic housekeeping, the puffer fish is a neatnik who keeps the trash under control, while the rest of us are pack rats hoarding junk DNA.Well said PZ!!1
There's a lot of thought these days going into trying to figure out some adaptive reason for such a sorry state of affairs. None of it is particularly convincing. We'd be better off reconciling ourselves to the notion that much of evolution is random, and that nothing prevents nonfunctional complexity from simply accumulating.
Watch for a few more postings on the remaining 45% of our genome then get ready to vote again. I'm hoping for a better result next time!
1. I used to know someone named Paul Myers who would never had said such a thing on talk.origins. Any relation?
[Image Credit: The junk DNA icon is from the creationist website Evolution News & Views.]