Science Explained: Who’s your daddy (genetically speaking?)

The Neandertal genome has been sequenced!  It’s in tomorrow’s issue of Science. I don’t know what kind of dork it makes me that I just screamed this to my office so that they know (I was met with blank stares), but I don’t care.  I’m so excited about this.  It isn’t complete, but a method has been developed to fill in gaps in the genome, and there is enough information to tell us some cool shite.

The History:
Neandertals showed up in the fossil record about 400,000 years ago, lived in Europe and Asia (including the Middle East), and disappeared approximately 30,000 years ago.  It is estimated that Neandertals and modern humans first interacted 80,000 years ago.  So far, only the DNA from the mitochondria, the cell’s power plant, which has its own highly variable mini-genome, has been sequenced in Neandertals.  The problem is that in modern day humans, the sequences are so different (as opposed to the nuclear genome), that trying to match the sequences between Neandertals and humans is not meaningful-there’s too much variation between humans, let alone, humans and Neandertals.  What’s needed is a comparison of the human genome (which we know) with the nuclear genome in Neandertals.  The human genome doesn’t vary much between individuals (relatively speaking), so the comparison could be informative.

Why we want to know:

Simply put, humans and Neandertals look different from each other.  We also look a lot alike.  The genome can help us understand how related are we genetically, which tells us whether the two species bred at one point, at roughly what point in genetic history, and exactly how much we have in common genetically.  Think about it this way: There is roughly 85% similarity (or homology, in science-speak) between human and mouse genomes.  Yet we look pretty different (most of us, anyway).   Without understanding genetics, I certainly wouldn’t have suspected that we had that much in common with mice.  I’m super curious about how much we share with Neandertals to understand where we come from genetically.

The problem:

Neandertals and modern humans share common ancestors in the last 500,000 years, and the known genetic variation between humans and Neandertals isn’t much different from what’s seen between modern humans, at least as detected by previous sequencing attempts.

The solution:

Kick ass technology, that’s the solution.  This research group cleaned up the method of sequencing, DNA isolation, and clean room technology combined with ultra-efficient sequencing methods employed today made the difference.

Methodical details:
1. The genome has been sequenced from three Neandertal individuals from geographically distinct sites.

2. Sequences were compared with each other, five modern-day human genome sequences, chimpanzee, rhesus monkey and mouse genomes.

3.  Bacterial DNA was degraded with proteins that are known to target only bacterial DNA.

4. Mitochondrial DNA told the researchers that the sequences were from three different individuals (it’s super variable, so it is a good marker for different individuals-this is a forensic trick too).

What they found-the short list:

1. Europeans and Asians share 1%-4% of their genomes with Neandertals.  Africans share none of their genomic information (as far as anyone knows) with Neanderthals.  This suggests that Homo Sapiens and Neandertals interbred during migrations of Homo Sapiens onward to Asia and Europe.  White?  Asian?  You’re a genetic mutt, dude.  (But then, aren’t we all?)

Similarity of Neandertal and human genomes.

2. Genetic evidence of positive selection between Neandertals and humans was found.  This means that changes were seen in the human genome that favored positive evolutionary movement toward favorable traits.  This kind of selection was observed in particular for cognitive and cranial development.

What does it mean?

This study can help us think about our own genetic history, develop new ideas about how human migration may have occurred through history, and learn about traits that may have developed through our evolution to the modern human.  It doesn’t mean everything is solved, but it helps unlock the mystery. It helps us begin to understand, genetically, who the Neandertals were, and how we are related, genetically and evolutionarily, to our ancestors.  It informs our thinking about the simultaneous movement of agriculture and our genomes as individuals and populations.  It gives us a different way to look at the world.

If you want to check out the original research, which I hope gets you as excited as it gets me, visit Science’s Neandertal special.

I dedicate this post to Elby Tackett, my high school science teacher, who told us when we hit the chapter on evolution: “I don’t believe in evolution, and I’m not going to teach you evolution.” Pointed to a picture of an ape and said, “that ain’t my grandpa.” Thanks for all you gave me, and thanks for all you didn’t.

1 Comment

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One response to “Science Explained: Who’s your daddy (genetically speaking?)

  1. scottkenemore

    Awesome! I shall stand tall as a proud Neandertal! Huzzah!!!

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