Stone Tools Speak

A common misconception about early humans and their relatives is that they were rough people with primitive tools. Even if our early relatives weren't as technologically advanced as we are, they were by no means primitive.

Yesterday in my class on human origins at the American Museum of Natural History, we studied stone tools, and an archaeologist named Glen came and actually made a stone tool right in front of us during the class. He finds that actually making stone tools helps him in his research because he can understand the process early humans went through to use and make them.

An Acheulean hand-axe from Douro Valley in Zamora, Spain.
Art by Josè-Manuel Benito Álvarez.

The process of making stone tools is known as flint knapping. To make a tool, like let's say a battle axe, flint knappers tap their blank (the stone that will eventually become the tool) with a billet (a tool used for striking the blanks). Blanks are made of stones like flint, obsidian, and chert because these stones are made out of the same material throughout so they break predictably. These stones are also hard, and they make good sharp tools. Billets, on the other hand, are made of softer material, like copper or antler.

Tapping the blank with a billet creates pressure waves in the rock which cause it to break into neat shards. When a shard breaks off, it has wave-like ridges on it. These ridges have the shape of the pressure wave that broke the rock. A pressure wave takes about a millisecond to break a blank, but the pressure wave marks stick around for thousands of years.  I think it's cool how a rock shard from thousands of years ago can document one millisecond of history.

Stone tools require skill to make and are extremely sharp. A fresh shard of rock is sharper than steel can ever be, but it dulls faster. This problem can be fixed easily by tapping off a fresh edge for the stone, or by just making a new tool. We got to test out the sharpness of leftover shards from the spearhead Glen made on apples, carrots and bananas, and they cut almost as well as any knife.

Tools made using the Levallois technique.
 Specimen from La Parrilla, in Valladolid, Spain.
 Art by Josè-Manuel Benito Álvarez.

Stone tools were not only useful for prehistoric humans, they help archaeologists today study and understand the past. Stone tools are great additions to the fossil record because, being stone, they preserve well and they can tell researchers many things, from what early humans were hunting to how advanced their language development was.

At first I was confused as to how stone tools could give us any information about language development, but now that I think about it, it makes sense. Complex tool stone tools were difficult enough to make that it would have taken pretty advanced communication skills to teach anyone how to make them. Also, as time passed, tools like spears became more popular than the good-old hand axe.  Spears, however, couldn't kill an animal with one blow. To use the spears effectively, early humans would have had to work in a group with an advanced plan of attack. Plans require good communication abilities.

It ends up that "primitive" stone tools are actually markers of an advanced society with a spoken language.

Why Be Bipedal?

I've been thinking about hominins lately, because of a class I'm in at the American Museum of Natural History on human origins.

When a primate fossil is found, researchers try to figure out what group of primates it belongs to. One of the key features for determining whether or not a fossil belonged to a hominin, is to tell if it was bipedal, ie. walked on two legs.Ways to tell are to see where the foramen magnum exits the skull (directly underneath for bipedals, back for quadrupedal), and if the femurs are angled in or not ( angled in femurs are a sign of bipedalism). It's funny that you can tell how an animal walked by its head, but it makes sense because the heads of quadrupeds stick out in front of their bodies while the heads of bipeds sit directly above their bodies.

There are countless theories about why hominins and their descendants (us!) gave up living in trees and walking around on all fours for standing upright. The thing is, bipedalism isn't completely beneficial. Bipedals are much more prone to lower back and knee problems, and they also tend to be weaker than quadrupeds.

A Man Running by Eadweard Muybridge

Hominins are bipedal, but the question is why? Why bother being bipedal in the first place?
Some benefits our early ancestors had due to being bipedal were: the ability to see over tall grass, the ability to carry children etc., more cooling regulation because less of the body is directly exposed to the sun, more energy efficient movement, and the ability to make and use tools and weapons. Some sexual selection may have also played a role.

The most intriguing theory of all of these, in my opinion, is energy efficient movement. Walking on two legs takes less energy than doing the same thing on four. Also, hominins have less hair and sweat more than other animals, allowing them to cool off while moving rather than having to stand in the shade for awhile. Freed hands allow hominins to carry provisions for long journeys. All these abilities allow hominins to persistence hunt, or run down an animal till it dies of exhaustion. This method of killing, still used today by some tribes in Africa, allowed hominins to obtain high caloric meat even without advanced weapons.

Some scientists get in heated arguments over the specific reason for bipedalism, but the truth is that all of these factors probably played a role, and we may never know exactly what happened.

Piltdown Man

One of the worst, and funniest, mistakes in the history of science involves the case of Piltdown Man.

Group of men examining the skull of Piltdown man.
Painting by John Cooke, 1915. Used with permission under Creative Commons.

In 1912 the skull and jaw of a hominin were discovered in a gravel pit in Piltdown, England. The skull was old, but looked modern due to it's large size. The jaw, however, was brutish and primitive. Piltdown Man led scientists to believe that large brains developed before bipedalism. This idea caused many other bipedal hominin fossils to be classified as apes due to small skull size, when these fossils actually did belong to hominins.

By the 1930s more and more bipedal hominin fossils with small skulls were discovered making Piltdown Man seem like an unusual case.

Finally, in 1953 Piltdown Man was found to be a fraud! The skull came from a modern human, which explained the unusually large size, and the jaw was from an orangutan. The bones were stained to make them look older, and the jaw attachment was filed down so it was not obvious that the bones weren't even from the same species.

Another bone found in the same pit as Piltdown Man was carved in the shape of a cricket bat. The person who put the bones there probably thought this would give the joke away since no animal has cricket bat bones. But no, this bat-shaped fossil was thought to be real too!

The identity of the hoaxer remains a mystery, but a man named Martin Hinton is the main suspect. He was an expert on rodent fossils who worked at the Natural History Museum. He had the technical knowledge to carry out the joke, and he also had a grudge against his boss, Arthur Smith-Woodword, who became one of the main supporters of Plitdown man.

I found out about Piltdown Man in the book The Accidental Species: Misunderstandings of Human Evolution by Henry Gee, and I just had to do a blog post about it. The case of Piltdown man illustrates how important it is to question and evaluate scientific discoveries before accepting them. It is hilarious how a joke like that went on for 41 years.

Psycopaths

The other day I went to the library near 116th Street in Manhattan and picked up a book called The Psychopath Inside by James Fallon. I've read a couple books on psychopaths before (The Psychopath Test by Jon Ronson, and  Confessions of a Sociopath by M. E. Thomas), but this particular book from the library interested me because it was written by a neuroscientist who was a borderline psychopath himself. Actually the only thing that kept him from being a full-out killer psychopath was that he hadn't killed anyone and did not have the desire to do so.

The question is why isn't he a killer when these other similar psychopaths are?

Psychopaths are known to lack empathy but are gifted at judging situations in a purely rational sense. Psychopaths are often popular and successful people because they are so rational. Empathy does not get in the way of their climb to the top. Psychopaths are unafraid of danger or hurting other people, and as a result tend to hurt or endanger others without thought.

One of the reasons for their risk-taking is that psychopaths have little or no brain activity in their anterior cingulate cortex, the area of the brain responsible for hot cognition, or decision making based on empathy.

On the other hand, psychopaths have increased brain activity in their dorsal prefrontal cortex, the area of the brain responsible for cold cognition, or rational decision making. Genetics are thought to be responsible for the lack of activity in almost all empathetic parts of the psychopathic brain because psychopathy tends to run in families.

Now, why aren't all psychopaths killers? From what is known today, it seems that psychopathic killers were more likely abused as kids, while psychopaths with a nicer upbringing tend to simply grow up into ruthless adults.

This book is an entertaining read and I would recommend it to anyone interested in neuroscience.