A discussion between species
Human: I am the mighty human, pinnacle of the evolution: I have the most advanced and complex genome with 25,000 genes and an impressive 3 billion base pairs in my DNA, you know these letters like A, T, G, C which make my genome. 3 billion of them!
Pufferfish: Come on. Your genome is just full of junk, 90% of it is completely useless! It’s full of dead viruses that infected your ancestors long ago and you never cleaned it up. Look at my genome, I have just as many genes as you, but I don’t need to waste 3 billion base pairs of DNA for that, just 400 million is well enough. Yes, I pack as many genes as you in a genome 10 times smaller! That’s what I call optimization!
Human: I’m not full of junk DNA! This 90% of DNA I have is useful, biologists are just too stupid to figure what’s is for. Surely the mightiest species on Earth cannot have 90% of useless DNA. What I say, the biggest the genome the more complex the organism.
Onion: I totally agree with you! But look at me, I am an onion of species Alu cepa, with 16 billion base pairs, that’s 5 times more that you human! You see, I am the ultimate complex creature, the greatest achievement of evolution.
Human: Hmm…
Pufferfish: Seriously? You think the biggest genome the best? I feel like I’m hearing this stupid lungfish. It has a gigantic amount of DNA, 130 billion base pairs. That’s 300 times my genome size, but do you think it is more complex and advanced than I am? The lungfish looks dumb compared to me. I can even make beautiful sculptures in the sand.
Baker Yeast: You’re cheating here, that’s a different species of pufferfish that does that*. But anyway, I agree with you that a small genome is an optimized genome. Look at me: 12 million base pairs only, that’s 30 times smaller than you!
Pufferfish: That’s cheating, you have only 5,000 genes. We animals often have between 15,000 to 30,000 genes so of course we need more DNA. As a vertebrate, I’m still the best. And anyway, you’re not even a multicellular organism.
Baker Yeast: You’re just a bunch of speciesists, I’m out of here…
Explanation
I recently read a very interesting new book “What's in Your Genome? 90% of Your Genome Is Junk” by Laurence A. Moran, in which he argues that our knowledge of genomics points to the fact that 90% of the human genome is useless junk.
This idea is not new, but it has become unfashionable in the last 20 years, without good evidence, the author argues. Most of our genome is still junk, and a central argument is that many other species don’t need that much DNA, or have much more without any “good” reason like the organism’s complexity.
You can buy the book here if you want to learn more.
* Takifugu rubripes and Dichotomyctere nigroviridis (the small genome one) vs Torquigener albomaculosus (the sand sculptures one)