Insights into Early Hominin Communication

A recent article published in Science looked to the skull shapes of early hominins, a group comprised of our now-extinct closest ancestors and ourselves, as a prediction of what sort of auditory sensitivity they were capable of, with interesting results. The shape and size of the auditory apparatus in animals affects the intensity with which each frequency register is perceived. In the study, the inner ears of early hominins, chimpanzees and modern humans were scrutinized, and the modeled ear parts of each were used to make predictions regarding the frequencies that were more easily heard, and the results were plotted as shown below. 

Fig. 1: Sensitivity to sound over a range of frequencies (article in discussion)

In the figure, the y-axis corresponds to the log of the ratio of sound power to reach the cochlea, Pcochlea, versus that of the sound source, Po, as a measure of the perceived sound intensity. The researchers conducting the study were able to show that the early hominins had a higher sensitivity to sound at around 3kHz than both chimpanzees and modern humans and generally higher sensitivity to lower frequency sounds as well, showing a decrease in sensitivity at higher frequencies that is more similar in trend to the hearing curve of chimpanzees than it is to humans. Modern humans, in contrast to the others, have a similar sensitivity curve at lower frequencies but extend hearing to higher frequency sound, dropping off near 4kHz frequency. In analyzing this finding, the researchers came to the conclusion that the adaption to a wider frequency range of hearing in modern humans was imperative for the development of consonants in human language. The researchers considered that the phonemes t, k, f and s in particular are associated with higher frequency sound and that the ability to perceive sound over a wide range of frequencies makes these sounds more distinct from each other. Since early hominins were incapable of perceiving the upper frequency range that modern humans can, the researchers postulate that communication between the early hominins would have been vowel-intensive. They make a point, however, of stating that this finding does not confirm any information about the extent to which early hominin language was used or developed; early hominins may have used a “low-fidelity social transmission” form of communication similar to that of modern chimpanzees. Nevertheless, the skulls of these early hominins have given us another insight into what life was like for some of our earliest ancestors.

The complete article on the differences in sound perception described above is available here. While the article is heavy on jargon, the results and discussion sections can be understood without fully understanding the early talk of ear anatomical differences. 

Also, please let me know your thoughts on this trial article in the comments. I am trying something new with the posts here, providing brief summaries of emerging science rather than explanatory articles of everyday phenomena. Feedback helps me decide what content I post. Thanks!

Boiling Water at High Altitudes: A Representation of American Scientific Literacy

A recent survey by the Pew Research Center found that Americans are more likely to answer correctly questions related to basic science concepts than to scientific understanding [1]. Among the bank of questions, ones such as which layer of the earth is hottest and whether uranium is used in nuclear energy were answered correctly more often than ones such as whether the amplitude of sound waves causes its loudness. The question answered incorrectly most often was whether water at higher altitudes boils at lower temperatures with only 34% of respondents knowing that, indeed, it does.

Fig. 1: Results of Pew Research Center survey (Pew Research Center, same as reference 1)

Public scientific literacy is an important goal to work towards for developed countries. As Cary Funk and Sara Kehaulani Goo of the Pew Research Center posit, the ability to understand scientific concepts is crucial to people being well enough informed about current issues such as GMOs and the energy crisis to make educated decisions in the polls. Scientific literacy also makes daily life easier by finding more efficient solutions to everyday problems.

As a small step towards improving scientific understanding, let us discuss why it is easier to boil water at higher altitudes.

Liquid water and water vapor exist in a sort of equilibrium. There are a number of factors that can shift this equilibrium, but one we interact with daily is temperature. Say you spill a glass of water. Of course, a large spill would require immediate attention, but if only a thimbleful of water was spilt, some would be inclined to let it evaporate. Evaporation involves two main processes at play. First, the water is receiving kinetic energy from its surroundings in the form of heat energy. Second, the water is in higher concentration in the spill than in the spill’s surroundings and therefore a concentration gradient is formed at the water’s surface.

So what has this all got to do with boiling water? Well, water boils when transforming into a gas. Therefore, boiling water is a phase transition described by the equilibrium between liquid water and water vapor. Besides temperature, pressure also affect liquid-gas equilibrium as described by the ideal gas equation,

                  1.       PV=nRT (P is pressure, V is volume, n is number of molecules in moles, R is the gas
                   constant, T is temperature)

LeChatelier’s principle states that a system in equilibrium will move away from an induced change. In the case of an increase in pressure, we can see that if n and T remain the same then the ideal gas law describes a shift to decrease V, volume. On the other hand, a decrease in pressure should cause a shift towards a higher V. This means that at lower pressures, water prefers to exist in a gaseous state and the equilibrium shift will cause the water to boil. This is the foundational concept of rotary evaporators, which use the concept of reduced-pressure boiling to remove solvents.

Fig. 2: Deriving atmospheric pressure in atm's (Pearson)

Now all that is left is to link pressure to altitude, which isn’t too hard. By definition, atmospheric pressure is defined as the weight of the atmosphere over an area at sea level [2]. For example, one inch of land at sea level partitions a pillar of atmosphere weighing 14.7 lbs, so atmospheric pressure in PSI is 14.7 lbs/in². A logical extension of this concept would tell us that at any altitude greater than sea level, the pillar of air would be shorter and would consequently weigh less. This is the missing link we were searching for between pressure and altitude. Putting all of the above information together, we see that a decrease in pressure causes liquid water to favor boiling and that an increase in altitude causes atmospheric pressure to decrease. Therefore, water boils easier at higher altitudes.

Scaling the results of the survey to education levels, the Pew Research Center also found a correlation between higher education and scientific knowledge. But this is not a given. Even as college students, we must all work towards insuring that we are among the scientifically literate ready to contribute educated opinions to today's social debates.

Approaching Herbalism from a Scientifically Literate Perspective

Is there really a founding for believing in herbal medicine? This seems to be a question many Americans are asking in a time when the concept of “human is better” is waning in favor of a return to an attitude that acknowledges we have a lot to learn from nature. Much of herbal medicine may seem like hocus-pocus, but scientists are not as against herbalism as some would think.

A first thought when someone mentions herbal medicine might be something along the lines of dried seahorse and mummified gecko. This is especially true for Americans where there is a high Chinese cultural medicine presence and where such practices are often caricaturized by the media. However, not all herbal medicine is so strange. Some common examples of herbal medicine practice could be honey-ginger tea for a sore throat and aloe (Aloe vera) for sunburns, both of which can be commonly bought in major store chains. As it turns out, much of the world uses some form of herbalism [1]. This shouldn’t come as a surprise. It is against human nature to accept illness as it comes, so wherever there are people there is likely to be medicine as well. But living in the time we do, both traditional herbal medicines and contemporary scientifically produced medicines are readily available. So which should we choose?

Fig. 1: Herbal medicine utilization by country (ClubNatu, same as source 1)

Herbal medicine is steeped in traditional medicine practices that developed before the scientific method and its instruments were available. Yet even so, many herbal remedies have come about through a rather logical process. Take even a fictitious, highly religious pre-scientific society where medicines are attributed to gods. If a medicine doesn’t heal its patient, then the instinct is to throw it out primarily because it’s useless and perhaps also because it makes the gods look bad. Our ancestors were smart enough to develop a working knowledge of herbs through thousands of years of trial and error, a highly valued logical test still used today in medicine development.

The argument some give in favor of a return to herbal medicine is that it’s more “natural” than modern synthetic drugs. This is not a well-based argument from a scientific perspective. Instead, we should consider factors such as effectiveness, side-effects, general safety of the herbs and the ecological impacts of its widespread prescription, each of which must be individually assessed per herb. The effectiveness of herbal remedies is a subject of increasing research attention as many have proven to possess clinical efficacy. Aspirin, for example, emerged from a more mild treatment of salicylic acid, a chemical found to exist in the bark of the white willow (Salix alba) tree used in traditional medicine. It has recently become a growing practice to scientifically test a wide number of natural products and traditional remedies as a high-throughput system for scouting out potential new treatments. Some herbal remedies have also been found to offer their effects with less side effects than modern medicine [2]. This could be due to a plethora of possible reasons including active dosage or the presence of other compounds to neutralize negative effects.

Fig. 2: Most popular natural products (including herbs) in the United States (NCCIH)

So where do herbal medicines fall short? All medicines have their associated risks, but a lack of herbal toxicity knowledge and of prescription guideline enforcement brings into question the safety of some herbal medicines [3]. The ecological effects of manufacturing herbal medicines must be considered as well. Paclitaxel, a drug with anti-tumor properties listed on the World Health Organization’s List of Essential Medicines, is a natural product from the bark of the Pacific Yew (Taxus brevifolia) tree [4]. However, wild-crafting this compound would devastate the tree population. Thus there is an inherent economic limitation on herbal paclitaxel, and so the synthetic generation of this natural compound is now the main route of production.

Herbal medicine is a topic that has been making a comeback under the realization that we have much more to discover about our medical pasts through a scientific approach. Personally, I am inclined to believe this is a step in the right direction since it is never bad to know more about plants that could potentially save our health. After all, it takes just one paclitaxel to make the search worth it. Social opinions on herbalism as a form of alternative medicine are shifting towards the positive, and as scientifically educated individuals we should keep ourselves updated on this movement.  

Is That a Point?

If I gave you a sheet of paper and asked you to draw me a nickel, you’d probably draw me a circle roughly an inch in diameter, maybe labeled with a "5₵". If I asked you to draw me a mite, the smart alecks out there would probably dot the piece of paper and give it back. If I asked for a realistic drawing of an atom, the same group would likely hand me back the blank page. This sort of answer is likely meant to be taken as a joke, but it also provides us with an insight into the limitations of human visual resolution.

Human eyes are anything but perfect, and some are less perfect than others. And as the silly drawings of the mite and the atom suggest, the smaller the object the harder it is for the human eye to resolve. By the international standard of measuring human visual resolution, good vision is defined as 20/20 (feet system) or 6/6 (meter system), meaning that someone with 20/20 vision can resolve what a person should be able to see (by designation) 20 ft away at the intended distance [1]. Someone with 20/40 vision sees at 20 ft what someone with 20/20 vision can see at 40 ft away, and someone with 20/10 vision sees at 20 ft what someone with 20/20 vision can see at 10 ft away. As objects get smaller, they seem to us as tending to a point. This occurrence is often referenced in physics where a source with radius r a distance d away from a sensor where d>>r (d is much greater than r) can be approximated as a point source.

But how exactly do we characterize this phenomenon, and at what distance does leaning forward while squinting intently seem… pointless? Let's take a look at the diagram below:

Fig. 1: A Spherical Object Viewed at Different Distances (Orig.)

 On the left side there is a spherical object of radius r₁ being observed by the first eye at a distance d₁ so that the object fills the observer’s field of view (denoted by the first set of dashed lines). The circle surrounding the object with radius r₂ represents the same observer’s field of view at a distance d₂ where d₂>d₁. The corresponding angles are drawn in and labeled as θ₁ and θ₂. From this diagram, we can obtain the equations

                                                                         1.       r₁=d₁tan θ₁

                                                                         2.       r₁=d₂tan θ₂

                                                                         3.       r₂=d₂tan θ₁

Dividing equation 1 by equation 3, we receive the statement

                                                                        4.       r₁/r₂= d₁/d₂

This equation tells us that as d₂ increases, the ratio of the original full-view object radius to the radius of the field of view at d₂ decreases as d₁/d₂=k/d₂ α 1/x (k is used to show that d₁ is a constant). The graph of 1/x is shown below:

Fig. 2: Graph of the Function f(x)=1/x (WyzAnt)

Where the x axis represents an increasing distance d₂ and the y axis represents the ratio r₁/r₂. This finding seems to agree with our experiences, doesn’t it? Namely, as we walk further away from an object it seems to decrease in size relative to our entire field of view, the size difference becoming less noticeable as distance increases further. If we were to walk far enough away, then the object would appear as if it were a point in our vision.

So we now know how to describe the way objects seem to decrease in size at far distances, but at what distance does any sort of difference in the object not matter? That is, when does the object become a point? Based on the human vision resolution assessment described earlier, we know that at 6m, or 20ft, the idealized human should be able to resolve a standardized interval of one arc minute, or 1/60° [2]. From rearranging equation 3, we receive the form

                                                                         5.       d₂=r₁/tan θ₂

Making the substitution of the maximum resolution for a 20/20 person’s vision, 1/60°, for θ₂, we produce the equation

                                                                          6.       d₂=3,438r₁

This equation says that an object with a radius r₁ can be seen from a distance a factor of 3,438 times its radius before a person with good vision can no longer sense its character beyond that of a point. This is like trying to see the face of a nickel from 146 meters away. While seemingly too far a distance to be visible, if we check equation 6 by substituting in the resolution corresponding to an arc minute at 6m, which is 1.75mm [3] (this can be checked with equation 1), then the distance returned is indeed 6m. With this information in mind, the next time you look up into the night sky I challenge you to think about just how big a star is compared to the twinkling dots you see above. Suddenly, it won’t seem so crazy to say we all live on the head of a pin.

Thank you guys for reading this post, and be sure to look out for more to come. If you want to be updated whenever I make a new post, sign up for email notifications on the right side column of the blog so you can have new posts sent directly to your email. Alternatively, if you send me a message on Google+ I'll add you to be notified when I post new content. If you have any suggested topics for future posts or you liked this post, let me know in the comments because I’d love to hear your thoughts. Thanks!