Thursday 21 December 2023

Creationism In Crisis - How We Have Evolved To Understand What Other Primates Are Saying

Can we decode the language of our primate cousins? - Medias - UNIGE

The UNIGE team wanted to find out whether the frontal and orbitofrontal regions of our brain activate in the same way when faced with human and simian vocalisations.
© Leonardo Ceravolo

One of the things that creationist frauds hate is the evidence of common descent in the form of redundant structures that now serve little or no function, but which were present in an ancient ancestor. Their problem with them is that they are evidence of common ancestry and make no sense as the work of an intelligent designer. What rational designer includes details and complications that have no function?

For example, humans and many herbivores such as rhinoceroses still have the enzymes for digesting the chitin exoskeleton of insects and other arthropods, even though they never eat them. However, the ancestral stem mammal was an insectivore, but there has been no selection pressure to remove the mechanism for digesting them as the herbivores evolved, so this retention is like a fossil, showing evidence of common ancestry.

Another example is the tendency for the hairs on our neck (and back, arms and shoulders if we have any hair there) to stand up when we are startled as an automatic part of the fight or flight response and a remnant of when making yourself look bigger was a benefit to a hairy ape suddenly surprised by a potential predator.

Now scientists at the University of Geneva, Switzerland, have discovered another largely redundant ability that only makes sense as something retained from an ancient primate ancestor which is present in modern primates where it still has a useful function, and in humans where its function is redundant for all practical purposes; humans subconsciously recognise the vocalisations of other primates.

This is just another in the list of redundant structures that are evidence of evolution and common ancestry:
What are some examples of redundant structures we have that were useful in an ancestor species, but which have little or no function in modern humans? Evolutionary history has left modern humans with various structures that may have had functional significance in our ancestors but now serve little or no purpose. These are often referred to as vestigial structures. Here are some examples:
  1. Appendix:
    • Function in Ancestor: It is believed to have played a role in the digestion of tough plant materials.
    • Modern Function: In humans, the appendix is considered a vestigial organ with no clear function. However, it can still be a source of health issues, such as appendicitis.
  2. Coccyx (Tailbone):
    • Function in Ancestor: It was part of a tail used for balance and movement in some of our primate ancestors.
    • Modern Function: In humans, the coccyx is a reduced and fused structure with no significant function related to balance or movement.
  3. Wisdom Teeth (Third Molars):
    • Function in Ancestor: Ancestors with a diet that included a lot of coarse, rough food may have needed extra molars for chewing.
    • Modern Function: Due to changes in diet and evolution, many modern humans do not have sufficient jaw space for wisdom teeth, leading to issues like impaction and misalignment.
  4. Plica Semilunaris (Third Eyelid or Nictitating Membrane):
    • Function in Ancestor: Protected the eye and kept it moist, common in many vertebrates.
    • Modern Function: Humans retain a small fold in the inner corner of the eye, but it is non-functional and often referred to as the "vestigial third eyelid."
  5. Body Hair:
    • Function in Ancestor: Provided insulation and protection.
    • Modern Function: While body hair still exists in humans, it is much finer and less functional in terms of insulation and protection compared to our furrier ancestors.
  6. Muscles in the Ear:
    • Function in Ancestor: Allowed more directional control of the ears, aiding in sound localization.
    • Modern Function: While some people can still move their ears slightly, these muscles are not as developed or functional in humans as in some other mammals.
  7. Goosebumps:
    • Function in Ancestor: Erecting fur for insulation or making the animal appear larger to predators.
    • Modern Function: In humans, goosebumps are a physiological response to cold or emotional arousal but have limited functional significance.
These vestigial structures provide fascinating insights into our evolutionary past, highlighting adaptations that were once advantageous but have lost their original purpose over time.
The Swiss scientists have published their findings, open access in the Journal Cerebral Cortex Communications. Their research is explained in a University of Geneva new release:
Are we able to differentiate between the vocal emissions of certain primates? A team from the University of Geneva (UNIGE) asked volunteers to categorise the vocalisations of three species of great apes (Hominidae) and humans. During each exposure to these "onomatopoeia", brain activity was measured. Unlike previous studies, the scientists reveal that phylogenetic proximity - or kinship - is not the only factor influencing our ability to identify these sounds. Acoustic proximity - the type of frequencies emitted - is also a determining factor. These results show how the human brain has evolved to process the vocal emissions of some of our closest cousins more efficiently. Find out more in the journal Cerebral Cortex Communications.

Our ability to process verbal language is not based solely on semantics, i.e., the meaning and combination of linguistic units. Other parameters come into play, such as prosody, which includes pauses, accentuation and intonation. Affective bursts - "Aaaah!" or "Oh!" for example - are also part of this, and we share these with our primate cousins. They contribute to the meaning and understanding of our vocal communications.

When such a vocal message is emitted, these sounds are processed by the frontal and orbitofrontal regions of our brain. The function of these two areas is, among other things, to integrate sensory and contextual information leading to a decision. Are they activated in the same way when we are exposed to the emotional vocalisations of our close cousins the chimpanzees, macaques and bonobos? Are we able to differentiate between them?

MRI scans with headphones on

A UNIGE team sought to find out by exposing a group of 25 volunteers to various human and simian vocalisations. "The participants were placed in an MRI scanner and were given headphones. After a short period of familiarisation with the different types of vocalisations, each participant had to categorise them, i.e. identify to which species they belonged," explains Leonardo Ceravolo, senior lecturer at the UNIGE’s Faculty of Psychology and Educational Sciences, and first author of the study.

These vocalisations were of the affiliative type, i.e. linked to a positive interaction, or of the agonistic type, i.e. linked to a threat or distress. The human vocalisations came from databases recorded by actors. The simian ones came from field recordings made as part of previous research. This study is the first of its kind to include bonobo vocalisations.

Bonobos, not so close cousins

The results show that for macaque and chimpanzee vocalisations, the frontal and orbitofrontal regions of the participants were activated in a similar way to human vocalisations. The participants were able to differentiate between them easily. On the other hand, when confronted with the "sounds" of bonobos, also close cousins of humans, the involved cerebral areas were much less activated, and categorisation was at chance level.

"It was thought that kinship between species - the ‘phylogenetic distance’ - was the main parameter for having the ability, or not, to recognise these different vocalisations. We thought that the closer we were genetically, the more important this ability was," explains Didier Grandjean, full professor at the Swiss Center for Affective Sciences and at the UNIGE’s Faculty of Psychology and Educational Sciences, who led the study. "Our results show that a second parameter comes into play: acoustic distance. The further the dynamics of the acoustic parameters, such as the frequencies used, are from those of humans, the less certain frontal regions are activated. We then lose the ability to recognise these sounds, even if they are emitted by a close cousin, in this case the bonobo."

Bonobo calls are very high-pitched and can sound like those of certain birds. This acoustic distance in terms of frequencies, compared with human vocalisations, explains our inability to decode them, despite our close phylogenetic proximity. "Are we capable of identifying the different emotional aspects of affiliative or agonistic vocalisations emitted by a chimpanzee, a macaque or a bonobo? And if so, how? These questions will be at the heart of our next research, which will involve analysing not our ability to categorise vocalisations by species but to identify their emotional content," concludes Didier Grandjean.

The ability to process verbal language seems unique to humans and relies not only on semantics but on other forms of communication such as affective vocalizations, that we share with other primate species—particularly great apes (Hominidae).

To better understand these processes at the behavioral and brain level, we asked human participants to categorize vocalizations of four primate species including human, great apes (chimpanzee and bonobo), and monkey (rhesus macaque) during MRI acquisition.

Classification was above chance level for all species but bonobo vocalizations. Imaging analyses were computed using a participant-specific, trial-by-trial fitted probability categorization value in a model-based style of data analysis. Model-based analyses revealed the implication of the bilateral orbitofrontal cortex and inferior frontal gyrus pars triangularis (IFGtri) respectively correlating and anti-correlating with the fitted probability of accurate species classification. Further conjunction analyses revealed enhanced activity in a sub-area of the left IFGtri specifically for the accurate classification of chimpanzee calls compared to human voices.

Our data—that are controlled for acoustic variability between species—therefore reveal distinct frontal mechanisms that shed light on how the human brain evolved to process vocal signals.


Processing and understanding non-verbal language are fundamental aspects of everyday life in human (Tracy et al.2015) and animal (Marler 1967; Leger 1993) communication. Their importance can sometimes even be greater than that of verbal communication since a short, powerful in-context vocal burst—for instance, an urgency signal—can easily be noticed and understood by other individuals (Leger 1993). A critical part of non-verbal language can therefore be represented by “affective” communication, especially through affective vocalizations, which are of particular interest for cross-species research. Indeed, the ability to express and understand such vocalizations is shared by several primate species, including Hominids, a taxonomic family that includes humans and other great apes (Gagneux and Varki 2001; Prado-Martinez et al. 2013). Such commonalities therefore open a critical window into the investigation of human brain structures recruited by social communication, for instance by studying these crucial abilities to perceive, process and subsequently categorize and classify affective vocalizations expressed by primate species. These abilities are known to recruit superior temporal, orbitofrontal and inferior frontal cortices in humans (Binder et al. 2004; Murray and Izquierdo 2007; Frühholz et al. 2012; Grandjean 2020) while these brain areas evolved a lot in primates (Semendeferi et al. 2002; Damasio et al. 1993). Studying cross-species vocal signals processing and categorization taking place in the cortex of humans, especially the prefrontal cortex, is therefore of crucial interest in understanding social interactions.

The Hominidae clade appeared between 13 and 18 million years ago (Perelman et al. 2011). Encompassing all living great apes including humans (Homo sapiens), chimpanzees (Pan troglodytes), bonobos (Pan Paniscus), gorillas (Gorilla subs), and orangutans (Pongo subs), as well as our extinct ancestors, this unique primate taxon is key to understanding the evolution of human behavior, physiology, communication and cognitive abilities. Very few studies have used bonobo vocalizations as stimuli (Kelly et al. 2017), despite sharing the same phylogenetic proximity to H. sapiens with chimpanzees, their behavior repertoire—of which gestures can be decoded by humans (Graham and Hobaiter 2023)—including their vocal communication are noticeably different (Hare et al. 2012.1; Gruber and Clay 2016; Grawunder et al. 2018; Staes et al. 2018.1). Despite a larger and more folded brain compared to other great ape species, human neuroanatomical traits are mainly considered to belong to a continuum in the primate brain evolution (Semendeferi et al. 2002; Herculano-Houzel 2009). For instance, findings in anatomical magnetic resonance imaging (MRI) have demonstrated the existence of a large frontal cortex in all great ape species—humans included (Semendeferi et al. 2002)—emphasizing the particular interest of investigating anatomical structures and related functions of the frontal regions. Moreover, the functions of the frontal lobe, often associated to problem solving, emotion processing and especially evaluative judgment, communication and language or even motor and sexual behaviors (Davidson 1992; Barbas 2000; Binder et al.2004; Barbas et al. 2011.1; LeDoux 2012.2; Frühholz and Grandjean 2013.1; Kambara et al. 2018.2), as well as their related brain structures are shared by most primate species. This includes two critical brain structures that are the focus of this article: the orbitofrontal cortex (OFC) and the inferior frontal gyrus (IFG).

Existing even in phylogenetically distant non-human primate species such as rhesus macaques (Macaca mulatta) (Rolls 2004.1), the OFC has similar neuroanatomical architecture and functions across the primate family tree. From humans to monkeys, studies have highlighted the roles of OFC in emotional memory (Barbas 2000; Barbas et al. 2011.1), emotional expression (Sander et al. 2005; Murray and Izquierdo 2007), executive functions (Barbas 2000) and integration of contextual information in emotional evaluation (Grandjean 2020). Interestingly, despite these shared evolutionary OFC functions in primate species, its role in heterospecific affective recognition, such as affective vocalizations, has rarely been investigated. In fact, recent functional MRI data have pointed out a greater enhancement of activity in OFC, in particular of its medial part, in the human identification of emotional voices compared to affective animal vocalizations including positive and negative calls expressed by chimpanzees, macaques and cats (Felis catus) (Belin, Fecteau, et al. 2008.3a; Fritz et al. 2018.3). More investigations on the role of the human OFC in this context are thus crucially needed …
Perhaps a creationists can do the necessary mental gymnastics to explain why an intelligent designer would go to all the trouble of giving humans an ability that they are not aware of and which serves no useful purpose, and why this is a better explanation that the obvious one - that this is just another example of what evolution from a common ancestor would produce.

Thank you for sharing!

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