A Prediction of Marine Plastic Debris Growth

Although it is common knowledge that plastic waste finds its way to the ocean en masse as evidenced  regions of high marine debris such as the great Pacific Plastic Gyres, there are few statistics that put exactly how much plastic enters the oceans into frame. A study published in February of this year looked to do exactly that, estimating that in 2010 an approximate 4.8-12.7 million metric tons of plastic entered waterways over 192 coastal countries that year.

This estimate was generated by taking into account local statistics for waste generation per capita and population growth trends to predict the amount of trash that shoreline countries produced within a 50 km region from the coast. An approximation of 11% plastics content for the produced waste was then applied, and transformations were imposed to convert total plastic waste to mismanaged plastic waste and finally to marine plastic debris. The authors of the study state that their estimate is one to three magnitudes higher than estimates made based upon gyre plastic content and justify this by reasoning these other estimates to only account for buoyant plastics. However, this large discrepancy between the predicted value and others brings the accuracy of the estimation into question. In the materials and methods section, the described transformation from mismanaged waste to marine waste was arbitrarily set at a percentage set of 15%, 25% and 40%, values that were deemed conservative based on a described estimation for the San Francisco Bay area.

Fig. 1: Projected plastic marine debris entering the ocean from 2010 on (Article in Discussion)

The study also estimated based on the same model that a cumulative 100-250 million metric tons of plastic waste would enter the ocean by the year 2025. This range was based on an extrapolation of population growth and plastic waste content growth rates in the past, and for this reason may be brought under scrutiny considering emerging efforts to stifle plastic waste pollution. However, the numbers produced in this study still has shock value, which lends them importance. Knowing that these enormous numbers are estimated based on current and past trends should in itself be a wake-up call since the implication is that our current lifestyle is unsustainable and resonates into the foreseeable future. In other words, this study is a call to action for all countries to set measures in place that will curb marine pollution currently and protect our future oceans.

The study goes into further detail about the extent to which efforts to reduce plastic waste in the near future will affect the amount of plastic trash that ends up in the world oceans and also gives a more detailed breakdown of the contributions of each country to marine plastic debris. It is definitely worth checking out and can be found in full text here. Thanks!

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!