The 234-bit gene that turns an ape into a man

You must have wondered why some of us are human while others are just apes. As I learned from an article that was sent to me by Peter F., all the difference may boil down to 117 base pairs on the 20th chromosome.

Study: Single Gene, Plus Some "Junk" DNA Turned Ape Ancestors Into Modern Man (Daily Tech)

Recall that all the information needed to create and run an organism is digitally stored in the DNA molecule, a sequence of base pairs. Each base pair is either AT or TA or CG or GC (the first and second letter correspond to the 1st strand and the 2nd strand of the double helix and they're locally distinguishable). Because you have 4 possibilities, the base pair carries roughly 2 bits of information.



The DNA sequence is divided into chromosomes. Humans have 23 pairs of chromosomes; all apes have 24 pairs of chromosomes. In total, they carry a few gigabytes of genetic information (3.08 billion base pairs or 6.16 billion bits), not far from an operating system. It's somewhat hard to believe that our not having one of the chromosomes is what makes us – apparently and only in some cases – superior relatively to the apes. There has to be a "positive difference" that favors us, too.




The researchers have previously looked for active genes – shorter sequences of base pairs that play some role (not just junk DNA) – and they have found essentially one solution: the MIR 941-1 gene (it also produces equally named MicroRNA molecules in all our, eukaryotic cells). The authors of the article in Nature Communications

Evolution of the human-specific microRNA miR-941 (Hai Yang Hu and 12 co-authors)

have used some now common methods to determine when and where this inherently human gene appeared for the first time. They found out it appeared between 6 million and 1 million years before Christ (or the present, for that matter: note that because of this parenthesis, this blog entry will become outdated in as little as one million years).

It's fun to repost the whole abstract. I hope that some other readers will, just like your humble correspondent, misunderstand some of this genetic jargon (and its content):

MicroRNA-mediated gene regulation is important in many physiological processes. Here we explore the roles of a microRNA, miR-941, in human evolution. We find that miR-941 emerged de novo in the human lineage, between six and one million years ago, from an evolutionarily volatile tandem repeat sequence. Its copy-number remains polymorphic in humans and shows a trend for decreasing copy-number with migration out of Africa. Emergence of miR-941 was accompanied by accelerated loss of miR-941-binding sites, presumably to escape regulation. We further show that miR-941 is highly expressed in pluripotent cells, repressed upon differentiation and preferentially targets genes in hedgehog- and insulin-signalling pathways, thus suggesting roles in cellular differentiation. Human-specific effects of miR-941 regulation are detectable in the brain and affect genes involved in neurotransmitter signalling. Taken together, these results implicate miR-941 in human evolution, and provide an example of rapid regulatory evolution in the human linage.

To be brief, our monkey ancestors became human when they escaped regulation and Africa. The individuals who want to return regulation to the human society want to revert the progress and make us apes again.



Ms Tereza Fajksová won the global Miss Earth 2012 (Biomiss 2012) contest promoting environmental awareness. The young woman, shown with some biomakeup, has been the hero of the local Filipinos for months, despite the fact that their local Miss Earth Philippines said that she wanted energy to be renewable while the winner's "positive" attitude to Nature means mainly that she loves fishing and mushroom hunting. ;-)

Fine, so it's probably a crucial gene that made the first humans – skillful apes.

It's irresistible to look at the servers of the University of California in Santa Cruz where the human genome and other genomes is mapped:

Gene turning apes to humans (UCSC)

These 117 base pairs (it's not an accident that the number is a multiple of three!) are those that are most responsible for ours feeling more skillful or, in many cases such as mine, at least cleverer than apes. In our way of measuring the information, it's just 234 bits.

In many respects, the digital information stored in the DNA and the digital information defining software is comparable, even when it comes to the size and its dependence on the abilities of the program or the organism. But these 117 base pairs are 234 bits or 29.25 bytes of information only. And they can make a human out of an ape? It's remarkable, isn't it?

It's like taking your code for MS-DOS and adding the following 29 bytes somewhere to the MS-DOS executables:

Behave like a userfriendly OS

I really wanted to write "Behave like a user-friendly OS and add all those nice windows, you chimp-like primitive operating system!" but I didn't have enough memory for that.

And this extra command would turn the MS-DOS into Windows. Isn't it cool? This represents anecdotal evidence that the abilities of an organism aren't simply monotonically increasing functions of the DNA size – even though we tend to think that it's pretty much the case for software. Instead, the "need for longer DNA codes" is just an approximate, overall condition, and sometimes very modest changes (MIR-941) and/or subtractions (missing 24th chromosome) can make a huge positive difference, too.

Nature stores the information in a much less predictable, more noisy way. This "holographic" feature of the DNA code is what makes it both impenetrable for a human reader as well as natural. On the other hand, the impact of pieces of software is much easier to be reconstructed which is why software is less subtle and man-made. Nature doesn't care about transparency and comprehensibility which is why it may afford obscure DNA codes whose importance isn't immediately clear for the DNA code's readers (She always understands Herself, She knows what to do, and She doesn't have to care for others).

To be more specific and geneticist-like, the birth of a new MicroRNA modifies the expression of hundreds of other genes – and the small code change therefore has a big, nonlocal effect.

Needless to say, genetics isn't the ultimate reason why I write these comments. I am secretly talking about physical theories. Deep, natural, physical theories often have very important consequences but one must learn and think hard to figure out what these consequences are. If someone isn't patient or smart enough and/or complains that the consequences aren't immediately obvious, he is implicitly demanding Nature to be overly simplistic, man-made, and user-friendly. But Nature isn't obliged to be like that and the person who complains is de facto an ape.

And that's the memo.