Are you more special than an onion?
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So, given that most of our genome isn’t actually genes, what does the rest of it do? Well, it’s complicated, and there’s still a lot we don’t know.
We can probably draw some kind of line between the DNA in our genome that has some kind of biological use, and the stuff that is genuinely junk. But the definition of ‘functional’ covers and awful lot of ground, and depends on – yes, you guessed it – how you measure it and who you ask.
Functional regions of DNA can act as control switches, turning genes on and off. They may be transcribed into RNA – not to make a protein, but to do something else useful in the cell. Then there are the structural bits, like telomeres at the ends of chromosomes, which effectively stop them from unravelling, and centromeres in the middle that are important when chromosomes are copied and separated as cells divide. And there might be other functions besides, that we are yet to discover.
Then there’s the rest. Some of this might be genuinely classed as junk – it’s just stuff we’ve accumulated through our evolutionary history. It’s not important and we can live with it, but we haven’t yet winnowed it out through natural selection. Some bits of junk DNA can even become useful over time, for example becoming control switches or other elements – like using a handy-shaped thingy you found in the garage to fix something, because it happens to fit the job.
And then there’s garbage – the stuff that really needs to go in the biological bin. This garbage DNA is positively bad for us and should eventually get booted out by evolution. For example, garbage DNA could cause unwanted changes in our genome that affect us in a bad way, like rogue retroelements that hop about, mixing things up and causing mutations. (Although, arguably, that might be a good thing in the long run by introducing new variations.) As Nobel-winning biologist Sydney Brenner wrote in 1998, ‘ Were the extra DNA to become disadvantageous, it would become subject to selection, just as junk that takes up too much space, or is beginning to smell, is instantly converted to garbage by one’s wife, that excellent Darwinian instrument. ’ Interesting that Brenner never considered his wife might take an alternative evolutionary journey and just move out…
So, size doesn’t matter, at least when it comes to genomes – it’s what you do with it that counts. And, as the only species that has been able to evolve to a point where we can read our own genetic code and start asking big questions about how it works and how it makes us who we are, we can perhaps be forgiven for thinking that the human genome is still pretty darn amazing – certainly more special than a vegetable... But while humans are indeed pretty darn amazing, on a purely technical level, it’s increasingly looking like our actual genomes are rather boring.
To wrap up, I want to read you a short excerpt from my first book, Herding Hemingway’s Cats: Understanding How Our Genes Work, of a conversation I had with the curmudgeonly evolutionary biologist Professor Dan Graur from the University of Houston, in which I asked him why we put so much importance on the contents and function of our own human genomes.
‘But humans want to feel that they’re special,’ I whine. ‘Am I not more special than an onion?’ I’ m treated to a dismissive eye-roll. ‘Either you have to assume that humans are the pinnacle of creation – that everything is functional and those organisms with more DNA than us have junk DNA but we don’t. Or you have to assume that humans are a regular organism that has junk DNA just like everything else.’
He brings up the example of Johannes Kepler, the German astronomer who helped convince the world that we revolve around the sun rather than the other way round. ‘Humans object every time to their demotion from the centre of the universe. Let’s face it, we are not special. People say, “Oh, the dinosaurs went extinct and we are alive!”
Actually the dinosaurs ruled the Earth for millions of years and the human race has been here for about 100,000 years, so let’s be modest, hmm? Evolution doesn’t care about the fact that we write books and get university degrees. ’
It's a humbling thought, but he’s right. To put it bluntly, evolution only really cares that you get laid and how many babies you make in the process. ‘That’s the only thing,’ he agrees. ‘If you look at the world with more objective eyes, you’ll see that we are nothing. There are more ants than humans, and in terms of number of species then it’s of course beetles.’ He tips a nod to the quote, or variations of it, attributed to the brilliant geneticist J. B. S. Haldane, who said, ‘If one could conclude as to the nature of the Creator from a study of creation, it would appear that God has an inordinate fondness for beetles.’
Although, as we covered in our episode on JBS Haldane, it’s not clear whether Haldane ever really said this pithy epigram, one thing is true: however you believe humans came into existence, and however fascinating you think we are, our genomes are nothing special. Sorry.
