Tag Archives: national museum of natural history

Can a museum object be more like a dog? New post at PLOS Sci-Ed

Dog owners out there may sympathize whit this: say you are outside walking your dog and are approached by friendly strangers who ask to pet him. Your dog just mediated a conversation with a stranger that would have not happen otherwise.

Like a dog, a museum object offers an excuse for strangers to have a conversation.

drill

Giant drill at the Perot Museum of Science and Nature. Photo by Lara Solt at Dallas News.

This giant drill illustrates hydro frakking at the Perot Museum of Nature and Science’s energy hall.  If this seems controversial it’s because it is: is the museum celebrating such technique, or opening up for debate among visitors?

For more examples and ideas, read the entire post at PLOS Sci-Ed.

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Dire Wolves on Ice

Ghost – a Game of Thrones dire wolf (HBO).

Game of Thrones fans, rejoice: the dire wolf is real. Here’s the bad news: the dire wolf went extinct 10.000 years ago. The enormous beasts who roamed the ice wasteland beyond The Wall are based on a real North American animal, who in turn left behind thousands of fossils. I have to admit that the dire wolf Ghost and his pack are the main reason why I continue to watch that show.

Ford in a snow quasi-wasteland.

The dire wolf is a close relative of the grey wolf and also (drum roll) of the dog. Meet my toned-down version of the dire wolf: Ford. Like Ghost, my dog also loves snowy wastelands. Ford is the only canine in a small pack of three (the two other members are human beings), where I am pack leader (or at least I like to think I am). That means Ford will obey me when I tell him not to chase that delicious squirrel or pounce on that fatty pigeon.

Ford.

Ford weighs around 60 lbs, which is about half the size of a large dire wolf. Large wolves could reach 175 lbs, and the ones featured on Game of Thrones were as big as a horse (fictional wolves don’t count: they had magical powers; the evidence of magical powers has not been found in fossils yet). If Ford was a dire wolf 10.000 years ago, he would have probably hunted on a pack with 30 other buddies, and something tells me this group would not be after squirrels or pigeons. Instead, dire wolves hunted for mammoths. 

A fantastic wall of thousands of dire wolf skulls. Photo by the Page Museum.

A wall of skulls

The Rancho de La Brea, in Los Angeles, is fossil site where thousands of prehistoric ice age animals were entrapped, their bones perfectly preserved in tar. In this tar pit, fossil bones of 3600 dire wolves were found. This is the largest amount of a predator specimens ever found in one site, and it way outnumbers all other mammals found in the same site. Saber-toothed cats are next on the list, but not nearly as numerous (“only” about 2000 are found on the tar pits). Much fewer prey animals were found, about 200 horses and 300 bison, which means there’s a ratio of ten predators to each prey.

What happened here? It seems one unlucky prey animal – say, a bison – would fall in the pit and become trapped. Right after, packs of dire wolves and saber-toothed cats would believe it an easy meal and jump in. Result: prey and predator – specifically one prey and dozens of predators – die together.

Today, the Page Museum displays finds from the tar pits (including an impressive wall of dire wolf skulls). Fossils are so numerous that the Page Museum recruits and trains volunteers to help with the ongoing excavations (volunteer finds are posted on the museum’s blog).

Dire wolf artistic depiction by Mauricio Anton.

Lions, tigers, and bears, oh my! (Or: the hunting habits of carnivore predators)

Before they went extinct, the dire wolf and the saber-toothed cat were as dominant predators as the lion and hyena are today in Africa. The high number of skeletons found on the tar pits suggested they (both dire wolves and saber-tooth) hunted in large packs and were able to tackle enormous prey – bison and camels, but also mammoths, mastodons, ground sloths, and Irish elk. Carnivores weighing more than 46lbs need to eat prey that is as large or larger than themselves. Those predators cannot survive only on small prey, because they would spend a disproportionally higher amount of energy hunting the prey than they would get by eating it. So, the efficient way to eat is to hunt for large prey. The devised strategy adopted by many carnivores is to form a pack. Grey wolves exhaust the prey, but lions or dire wolves, who are larger and more stockish, pounce and grab them.

From left to right: dire wolf, saber-toothed cat, short-faced bear, cheetah-like cat (Miracinonyx sp.), American lion. (Modified from Turner, A., and Anton, M., The Big Cats and Their Fossil Relatives. Columbia University Press: New York, 1997)

Extinction

The dire wolf’s cousin, the grey wolf, is now considered a top North American predator. But the grey only reached this post after many large carnivores went extinct. Both the grey wolf and the dire wolf co-existed with 10 other species of large carnivore: the puma, jaguar, two species of short-faced bear, florida-spectackled bear, black bear, scimitar-toothed cat, saber-toothed cat, grizzly bear, and the American lion. All 12 carnivores competed for similar prey. Most of those predators became extinct 10.000 years ago (ever wondered why there are no lions, tigers, or elephants in the US? Because they died off after climate change or food depletion). Now only the puma, black bear, and grizzly bear remain.

Compared to the grey wolf, dire wolves had shorter stouter legs and smaller brain cases. They also had stronger teeth, comparable to a hyena’s in its bone-crunching abilities (which probably means food was scarce and every bit of bone marrow was precious). Dire wolf teeth is more adapted for “carnivority”, which means they are not as versatile in eating alternatives (other carnivores, like bears, will eat even bugs and honey). All of that contributed to their demise.

Ford looks at his extinct canid relatives.

Survival of the coldest

But here’s a fact Game of Thrones did not tell us: dire wolves were creatures of warm weather! They preferred tropical or subtropical regions. One of the reasons the grey wolves survived and dire wolves didn’t is because the grey wolf’s hunting range extended to the cold arctic. During the Ice Age, the dire wolf was left behind, to die and disappear.

But I guess the appeal of a beast of the tropics does not suit Game of Thrones. Ford, for once, prefers snow and cold, and becomes very depressed on the summer. Instead of the dire wolf, Ford would have fit in perfectly in Winterfell.

Got lactase?

(Ms Felicia Gomez and Dr. Jibril Hirbo give a talk at the Smithsonian's Human Origins Topic. Photo by the author.)

The human is the only mammal who continues to drink milk throughout adulthood. Most mammals completely loose the ability to digest milk after weaned, a gradual process that starts as early as 16 weeks. Humans can normally digest milk for the first 5-7 years of life, but after that, lactose digestion is slowly lost, and most people become what we know as lactose intolerant. In fact, the majority of the world is lactose intolerant, to various degrees; not surprisingly, considering this is the norm in most mammals. Then why are some humans able to consume milk and drool over ice creams, butter and cheeses?

Lactose intolerance has someone else to blame: lactase!

Lactose is the main sugar present in milk. As a rule of thumb, sugars are carbohydrates whose names end in “ose” (think  glucose, fructose, galactose, lactose). The enzyme lactase  – where “ase” endings indicate an enzyme name – works as a little molecular engine, breaking down lactose into smaller pieces: glucose and galactose. Lactase is abundant in infant mammals, but much less present in adults. The deficiency of this breaking down enzyme results in lactose malabsorption and is the cause of lactose intolerance.

However, in many population groups where milk is a key dietary source, humans adapted and continue to digest lactose after adulthood. This trait is named “lactase persistence”, and I guess you could say it is the opposite of lactose intolerance.

(Pockets of lactase persistence shown in pie charts. Ingram et al, Hum Genet 124:579–591, 2009)

Lactase persistence is well know in Europeans

Lactase persistence has evolved independently in several population groups around the world. It is assumed the environmental pressures drove adaptation in pastoral communities who rely heavily on milk products for nutrition and even for a water source. In other words, if a population is required to consume milk derivatives, given time its DNA could adapt to process it. And have done so, a few times and in different places of the world.

(Two groups that have independly adapted to lactose digestion: the swiss and the masai. Photo credit: the evolution group at Berkley)

I first got interested in this topic after I participated on the “Human Origins Topic” at the Smithsonian, where Dr. Jibril Hirbo and Felicia Gomez, from the Sarah Tishkoff group, talked about their work (see top photo). They collect DNA samples from many african populations and track down differences in DNA sequences of specific genes. A single DNA nucleotide base change is named SNP, for Single-nucleotide polymorphism (pronounced as “snip”), and Tishkoff’s group has been cataloging SNPs for lactase persistence in african populations.

Lactase persistence in europeans is well known and documented, and is caused by the SNP C/T-13910 (the numbers represent the position in the gene where the DNA change occurs). 90% of northern europe (specially in Sweden and Denmark) is lactase persistence, and ~50% of southern europe (Spain, French).

The cause for lactase persistence in african populations was still unknown, and was studied by Tishkoff, whose findings were published in the  “Convergent adaptation of human lactase persistence in Africa and Europe“.

(photo from the evolution group at Berkley)

Capturing SNPs in remote african locations

In order to detect SNPs associated with lactase persistence, Tishkoff’s group collected and sequenced DNA from 470 individuals from 43 african ethnic groups (Tanzanias, Kenyans and Sudanese). A majority of this collection work was done by Dr. Jibril Hirbo, who explained his approach:

“The biggest challenge was to get to communities we intended to sample because of poor infrastructure. Once we got to our destination we usually approached the community leaders and talk to them about our research, then the leaders organize something like a ‘townhall” meeting where we explain our research to the villagers  and make sure they understand what we were doing. It was easy talking to the people because I spoke the local language and know the cultures…so I just broke it down to them in the way they could understand.”

The test – named LTT for lactose tolerance test – is very straightforward, as Dr. Hirbo points out:

“The sampling was in two part – initial blood/saliva collections for the study of genetic variation of human population and second lactose tolerance test that involved drinking the orange solution that contain lactose sugar that is found in glass of milk followed by monitoring blood glucose level in blood drops from finger prick over one hour period.”

The DNA collected from the saliva is brought to lab, and sequenced, to identify SNPs correlated to the lactase persistent populations. The correlation between SNP and phenotype (the presence of lactase persistence) can be obtained by matching the DNA with the results from the LTT.

They found that each population group has a different mutation that resulted in lactase persistence. None have the european SNP (C/T-13910), and instead, each of the tested african groups displayed unique SNPs (G/C-14010, T/G-13915 and C/G-13907).

This is a clear case of convergent evolution: where 4 distinct variants correlated with lactase persistence independently arose in the world. These genetic variation was associated with pastoral groups and its migrations. Tishkoff’s group even goes further to say that the pattern of genetic distribution might match the cultural and linguistic distribution in Africa.

(Scheinfeldta et al, PNAS vol. 107 no. Supplement 2 8931-8938, 2010)

Can we safely conclude that the genetic spread accompanies culture? Pastoral, ethnic, and lactase persistent groups appear to indicate that.

More cheetah-speed notes

  • Last Friday I attended the “HOT” (Human Origins Topic) event at the Smithsonian, where Dr. Jibril Hirbo and Felicia Gomez gave a talk about genetic variation in african populations and its possible correlation with cultural and linguistic spread. The speakers were very gracious and interesting. I will bring up their papers in a future post. Update: my commentary plus an analysis of lactase persistent trait in african populations can be seen here.

  • I also bought these three books in the Smithsonian bookstore: The Dolphin in the Mirror (Diana Reiss), The Whale – in Search of the Giants of the Sea (Philip Hoare), and Giant Pandas – Biology and Conservation (collection edited by Donald Lindburgh and Karen Baragona). I just finished reading the dolphin book, and I am very intrigued by the mirror test (a form of testing for an animal’s self awareness) when applied to  bottlenose dolphins. More soon. Update: post on Dolphin in the Mirror here

Forensic Friday

Forensic Fridays, phot by the author

I stopped by the Smithsonian National Museum of Natural History for Forensic Friday, where I talked to paleobiologist David Bohaska. He showed me 6 million year old fossilized vertebra from whales and dolphins. Last Friday’s theme was “Marine debris & ocean life”, and the scientists brought in a few marine mammals (whale, dolphin and manatee) bones, used to speculate the animal’s cause of death. I photographed the bones and injury sites, but I’m not sure yet if I  am allowed to publish the images. The fossils are part of off-the-shelf collections, not available to the general public, so I will need to clear it with the Smithsonian first. Regardless of publishing the photos, I can’t wait to share the stories I heard about those animals lives…