Ancient Human DNA Suggests Twisted Roots at Base of Human Family Tree
Scientists have sequenced DNA from the 400,000-year-old remains of an early human found in the Sima de Los Huesos cave in Spain. It not only shatters the record for the oldest human DNA sequence ever obtained, but is also forcing scientists to question what we thought we knew about human origins.
Traditionally, scientists have compared the measurements and proportions of these skeletons in order to place our ancestors along the human family tree and evolutionary timeline. The skeleton up top, from the Spanish cave, is classified as Homo heidelbergensis, a group of human relatives from Europe who, according to the bones, are thought to be the ancestors of Neanderthals.
But new and powerful DNA sequencing technology has given us the ability to stitch together sequences from older and more degraded DNA samples than we ever thought possible (I wrote about a 700,000-year-old horse sequence earlier this year for WIRED). The sequences in the Los Huesos DNA don’t agree with the old bone story.
The sequence shows that this 400,000-year-old DNA is most related to Denisovans, a group of early humans previously only found in Siberia (AKA “not near Spain”). It was also related to Neanderthals, which fits with the old idea, but suggests that there was a lot of interbreeding and migration going on in these groups, even before modern Homo sapiens had left Africa.
The genomic revolution is changing a lot about science, and the study of human origins is one of the fastest evolving (pun intended). This new info has confused the hell out of scientists, frankly, and there’s a lot of work to be done.
The roots of our family tree tell a twisted and gnarled tale, written in fragmented sentences, but modern technology is beginning to bring those lost words to light. Hopefully they aren’t jibberish.
I’ve got passion in my brain and I ain’t afraid to show it…
Illustration above by Jon Perry, whose animated series about evolution, Stated Clearly, is really worth checking out (also featuring great illustrations of Rosemary Mosco from Bird and Moon!). They have a Kickstarter going to fund more videos, and if you think the world could use more fun and positive ways to teach the beauty of genetics and evolution (and we all know that the world could use more of that), then consider supporting them.
Here’s one of their videos, What Is Evolution?
Beyond “The Selfish Gene” to “The Selfish Network”
The grasshopper is the gene, and the locust is the networked swarm.
David Dobbs has a very interesting article out in Aeon about the incompleteness of “selfish gene” theory and the rise of an idea called “genetic accommodation”. Accommodation is the appearance of a trait, say larger muscles or faster running, in response to the environment, within a single generation (it sounds Lamarckian, but it’s not). Dobbs’ article is full of some pretty high-level biology, but it’s a very crucial lesson on the realities of natural selection in complex creatures and complex populations.
Chances are, if you’re a student of genetics and evolution, you know about Richard Dawkins and “the selfish gene”. This theory, and the book of the same name, places the gene at the center of evolution, and presents the organism, you or I, as vehicles for their replication and selection. It is beautifully written, well thought-out, and it made Dawkins the star he is today.
Unfortunately, the idea of “selfish genes” is incomplete, at least according to many modern evolutionary biologists. In complex creatures, there are a host of changes in appearance, ability and behavior (so-called “phenotypes”) that do not result from discrete genetic mutations, but rather from changes in how those genes are expressed, and these often show in the same generation, not just in offspring.
Dobbs gives us the example of the locust and the grasshopper, which ( I did not know this), are the same species! When food goes scarce, the lone hopper morphs into a swarming species that can lay waste to fields at Biblical proportions. These changes are not at the level of DNA changes within the gene, they manifest in how that DNA is read and turned into proteins or whatever the gene product turns out to be.
There are two important keys here: 1) Genomes are full of mutations and differences, most of which are silent and don’t contribute to natural selection, and 2) in complicated creatures such as us, genes are subject to complex, squishy, variable networks, and it’s mutations in many genes within and between networks that often lead to phenotypes.
That’s an incomplete oversimplification itself, but if you’d like to dig deeper, read this PZ Myers piece on how evolution is about networks. As for me? I’ve studied molecular genetics for about ten years now, and while Dobbs is right that the simple “selfish gene” idea needs work, gene expression differences are also dependent on genes, and those genes can be mutated and selected, or not, so after a while this whole networked snake begins to eat its own tail.
Evolution is hard. Most people, if they even accept it, don’t get far enough in biology classes to see just how hard it is. In school, we begin our study of genetics with the study of Mendel’s peas, a simple and idealized example to demonstrate how statistics and ratios are at play in the distribution of genes. But then almost instantly, if we go on with our studies, we learn that these idealized scenarios are incomplete, and that’s not how the real world of natural selection and population genetics works. So we look for where our rules are broken, and we apply new, often complex, rules to fill in the gaps.
This is how science itself works. Our idealized classroom scenarios, like Dawkins’ “selfish gene” or Mendel’s peas, are important tools to have in our toolbox, but they are incomplete. It is important that learn to identify their deficiencies, and to use new observations to create new tools … and with them we are always working to build a better house.
Which we then hope is not flattened by a locust swarm.
Check out Die, Selfish Gene, Die by David Dobbs. What do you think?
I’ve been thinking a lot about strange fruits since last week’s episode on the ghosts of evolution that reside in our produce aisle. Lots of people liked that episode. That makes me very happy. In that spirit, I present this question:
What’s the most annoying fruit ever?
The answer, of course, is the pomegranate. But this isn’t about the pomegranate. It’s about the mango. And the mango comes in a very close second on my Fruit Annoyance Scale™.
I’m pretty handy in the kitchen. I know how to cut one. I’m just left disappointed every time. So much deliciousness remains stuck to that wacky, disc-shaped seed. My only choices are to throw it away or to gnaw at it like I’m afflicted with some sort of crazed, herbivoric bloodlust, covering myself in stickiness and drawing many a raised eyebrow from my wife.
But that little trick, that hidden seed, is part of the mango’s evolutionary magic, its very key to survival and reproduction.
If you watched the video, you remember that the avocado, with its ridiculously big seed, evolved to get swallowed whole, and be pooped out later, so they could grow far away and free from big tree competition. The only problem is that the moving truck-sized ground sloths and prehistoric elephants that munched on them in central America are extinct. Yet the avocado lives on, strangely, no longer subject to that cooperation. It’s an evolutionary anachronism.
That’s the story behind the mango’s über-annoying seed. In southeast Asia, the mango’s native lands, forest rhinos and Asian elephants, who love mangos, are some of Earth’s last remaining examples of the megafauna that dispersed so many of the world’s weird fruits (including papaya, durian, avocado, and many others).
The mango has evolved a stringy flesh that clings to its seed (and whoever took the photo above clearly spent hours excavating that thing). Rhinos and elephants find that just as annoying as we do, so they swallow them after only the tiniest bit of munching. After a long, strange trip through the belly of the giant mammal, that seed gets dropped off with its great reward: A dallop of fresh fertilizer.
When you look at an elephant or rhino, you’re looking at the last giant mammals to still roam dry Earth. Sadly, nearly all of them are critically endangered. I and others have often referred to those strange fruits as “ghosts of evolution”, but those great creatures are close to becoming ghosts themselves. That’s really sad. Sure, we’ve taken over for the large mammals in the mango-growing department, but we shouldn’t save one ghost to spite another.
I hope that you’ll never look at a mango, or avocado, or papaya quite the same way again. And maybe, when you consider the mango, you’ll consider these beautiful creatures:
Let’s do what we can to keep them from becoming ghosts, too.
A GIFset of Ghosts of Evolution
GIF-Ghosts of Evolution
GIFts of Evolution
I don’t even know. Creative post titles are hard, okay? Just watch it or something :)
P.S. - In the third one do I look like the world’s greatest magician or what?
New video: Ghosts of Evolution
There’s ghosts living in your grocery store. I promise. Just head over to the produce section and pick up a mango, papaya, or avocado.
There’s also gardens of ghosts lining the streets of New York City, same as hundreds of towns across the country. The ginkgo tree, known for its pungent, vomit-smelling seeds, holds ancient secrets dating from the age of the dinosaurs.
Check out my latest video to find out why these ghosts live on, discover that the ginkgo’s friends are all dead, and learn the answer to how an avocado is like a dodo.
Oh, and you’ll get to see an extinct giant ground sloth use an outhouse. That’s a YouTube first, I’m pretty sure.
As always, thanks for watching, and stay curious!
The 2013 “Dance Your Ph.D.” Winner is Swimmingly Good
University of Oxford’s Cedric Tan takes the winner’s podium this year with his part-synchronized-swimming, part-biology-lesson tale of how the sperm of brothers and non-brothers compete within, and with, the female to see who gets to fertilize the egg. The science of sexual selection sure can be fun, eh?