Science-- there's something for everyone

Tuesday, September 15, 2015

Did ancient hominids bury their dead?

Yesterday, I told you how Homo naledi was discovered. To refresh your memory, check out this picture:

Marina Elliott works in the Rising Star cave near Johannesburg, South Africa. (National Geographic/National Geographic)
Today, we'll discuss why this find was so important.

The very fact that so many bones were found in one place was critical. The six paleontologist spelunkers retrieved over 1500 bone fragments which were later assembled into at least 15 skeletons. That means that the researchers had specimens of different ages and of both genders, an almost unheard of scientific find. This gave anthropologists an unusually accurate picture of what these creatures were like. 

Thus, we know that H. naledi's physical features place it between those found in the genera Australopithecus and Homo.
We don't yet know how old those bones are, which means we can't be sure where H. nelida falls on our family tree. H. nelida seems to be intermediate between Austrolopithecus and Homo, but could have been contemporaneous with most of the species within those genera. Dating the fossils is going to give us critical information on how and when different modern physical traits first appeared. 

Just as importantly, how did those bones find their way into that remote cavity? Consider that although there were so many H. naledi bones in the cave, virtually no other species were found along side them. This was not a lair used by predators, hominid or otherwise, nor was the accumulation of bones due to flooding or other natural causes. There were no marks of damage or scavenging on the bones, so the cave was not the site of a slaughter or feast. And remember that the chamber where the bones were found is extremely hard to access. 

Lead researcher Lee Berger's working hypothesis is that the bodies were deliberately placed in the chamber, most likely by dropping them in from above. We have a name for procedures like this: it's called 'burial', and it's not an activity we would have associated with creatures that had brains the size of gorillas. 

Berger and the other researchers are continuing to study the fossils. Many more interesting conclusions are sure to come out of this amazing find. You can find some great photographs as well as an artist's rendition of the creatures giving a dead relative the old heave-ho in the National Geographic story by Jamie Shreeve. 

Berger, L., Hawks, J., de Ruiter, D., Churchill, S., Schmid, P., Delezene, L., Kivell, T., Garvin, H., Williams, S., DeSilva, J.... (2015) , a new species of the genus from the Dinaledi Chamber, South Africa . eLife. DOI: 10.7554/eLife.09560  

Monday, September 14, 2015

Homo Naledi discovered, thanks to small skinny cavers

We have a new member of the human family tree and I don't know which is more wonderful: the way Homo naledi was found or all the things we'll learn about our own evolution thanks to this discovery. 

Today, let's take a look at the discovery itself, which took place in October, 2013. We'll cover what this means tomorrow.

Lee Berger, a National Geographic Explorer-in-Residence, decided that it had been too long since he last explored. Five years earlier he (along with his then nine year old son) discovered Australopithecus sediba, a two million year old hominid, and had spent the intervening years analyzing that find. In 2013, he decided it was high time he got back in the field.

In Berger's case, the field turned out to be the Rising Star Cave system in South Africa. There, a caver named Steve Tucker inadvertently discovered a chamber full of hominid bones. Unfortunately, that chamber was extremely hard to access. Tucker and his fellow caver Rick Hunter lacked the expertise to safely collect the fossils, and Berger himself couldn't even get to the chamber. Take a look at the graphic below to see why. 

A social media request for small, skinny individuals with scientific credentials, caving experience, and no claustrophobia brought in nearly 60 applicants, out of which Berger selected six women: Marina Elliott, Hannah Morris, Becca Peixotto, Alia Gurtov, Lindsay Eaves and Elen Feuerriegel

Safely removing the fragments without crushing the fragile pieces of bone or getting in each other's way was a delicate task requiring yoga poses and cramping muscles. And that was after they made their way into the chamber.

Nonetheless, the 'underground astronauts' mostly Ph.D. students in anthropology, were all reluctant to leave at the end of their two hour shifts, often doubling or even tripling their time in the chamber.

Working in three person teams, the six women managed to retrieve over 1500 bone fragments, all from the same human ancestor species, now called Homo naledi. Naledi means 'star' in the local language.

Tomorrow: what we've learned from this find.

Monday, September 7, 2015

Start your senior year at 11:00 am?

It turns out that teenagers were right all along when they complain that high school starts too early. That actually isn't news to anyone who has had to drag an adolescent out of bed in the morning. However, the recommendations made by Paul Kelley of Oxford University and his colleagues may surprise you. They suggest that 18 year olds start school at 11:00 am.

First though, why is it that teenagers have so much trouble getting out of bed in the morning? The simple answer is that they can't get to sleep at night. This isn't a demonstration of lack of character but rather of biology, or more specifically of circadian rhythms. Every cell in our bodies is tuned to a 24 hour cycle, and the master controller for all our cells resides in the hypothalamus. The sleep-wake cycle happens to be an extremely vulnerable part of that 24 hour cycle. Throughout the day, we excrete competing hormones and neurotransmitters that increase either alertness or sleepiness. In adolescents, it just takes longer to reach a critical mass of sleepiness signals than it does in older adults. Thus, going to bed earlier doesn't help teenagers get more sleep. They are wide awake until late in the evening no matter what time they go to bed.

This means that when students get ready for school in the morning, they're likely to have had much less sleep than they need. A typical 15 year old gets less than 7.5 hours sleep on a school night, but over nine hours on a weekend when he's free to sleep as long as he wants. This has repercussions not only for learning, but for health and safety. Sleep-deprived people are at greater risk for emotional problems, depression, weight gain and even car crashes.

The researchers based their conclusions on sleep pattern studies that show that 10 year-olds tend to wake up naturally at 6:30 am, 16 year-olds at 8:00 am and 18 year-olds at 9:00 am, and allowed each group two hours between wake time and start of school. Therefore, according to them, fifth grade should start at 8:30 am and high school at either 10 or 11 am. Personally, I think two hours to get ready in the morning is probably excessive for most people unless they have a long commute to school. However, schools that have implemented these late start times have seen significant student improvements.

Even the United States Air Force Academy is testing later start times for first year students and finding that those late-starting students do better not only during the first class of the day, but in all their classes. More school districts are starting to pay attention to these results, which is very good news for students.

Kelley, P., Lockley, S., Foster, R., & Kelley, J. (2014). Synchronizing education to adolescent biology: ‘let teens sleep, start school later’ Learning, Media and Technology, 40 (2), 210-226 DOI: 10.1080/17439884.2014.942666