At the Origins of Sciences

ideas were emerging, they were not sufficient to explain the appearance of human and animal beings on Earth, facing the strong belief in divine intervention for the creation of life. Due to the power of religion, evolutionary thought was thus ignored until the Age of Enlightenment. The 18^th century was indeed the time of an important philosophical revolution, in which the thirst for knowledge enabled the theory of evolution to finally reach a milestone. Following this great period of scientific knowledge, the first conceptualizations of evolutionary mechanisms emerged in the 19^th century with the concepts of transmutation of species and natural selection, made by Jean-Baptiste Lamarck and Charles Darwin respectively. Nevertheless, Darwin’s ideas of fitness and phylogenetic branches initiated the

“Darwinian revolution”, in which the fact that humans are primates and thus animals among others is finally recognized in sciences. His theories were strongly debated across the scientific community, even if his friend, Thomas Henry Huxley strongly supported him.

Nowadays, through the modern synthesis of evolution, evolutionary mechanisms are recognized as key factors to explain physiological and behavioural processes in humans and other animals.

2.1.1.1. At the Origins of Sciences

The intuition that species change over time and descend from a common animal is not a modern theory. In fact, it is probably one of the oldest concepts in science. Indeed, Anaximander of Miletus (610 – 546 BC), often considered as the first evolutionist, already suggested that the first animal on Earth lived in water and that humans could be the descendants of a primitive fish (Kočandrle & Kleisner, 2013). However, influential philosophers such as Plato (428 – 648 BC) and Aristotle (384 – 322 BC), who believed in a divine intervention for the creation of life, questioned this first evolutionary perspective. In the same way, later in the Roman Empire, Lucretius (99 – 55 BC) described in his poems “De rerum natura”, survival mechanisms in the development of life (Holmes, 2007). Nevertheless, he was also criticized by Cicero (106 – 43 BC), a major philosopher at that time, strongly influenced by religion (Cicero, 2003).

Crossing the Middle-Age and the Renaissance period, evolutionary thought finally reached a milestone during the Age of Enlightenment (18th). Indeed, the word “evolution” took on its full meaning of progression with Charles Bonnet, in his concept of future generation development: the theory of pre-formation, in which female carry within them all future

generation in a miniature form (Pallen, 2011).

Additionally to this, Pierre Louis Moreau de Maupertuis was the first to describe in his book “Venus Physique” the mechanism of “natural selection” conceptualized later by Charles Darwin: “In the fortuitous combinations of the productions of nature, none but those that found themselves in certain relations of fitness could subsist, is it not wonderful that this fitness is present in all species that are currently in existence?” (Maupertuis, 1745, p. 197).

Similarly, Georges-Louis Leclerc, Comte de Buffon, like his future successor Jean-Baptiste Lamarck, argued that species are varieties modified by environmental factors from one original individual. He even suggested that humans and apes had a common ancestor.

However, the Comte de Buffon also believed that each species had an original form arisen through spontaneous generation and thus, that modifications specific to each species were limited (Pallen, 2011).

Finally, James Burnett, Lord Monboddo, probably ahead of his time, already suggested in the late 18^th century, that humans were the descendants of other primates and often compared the human species to other great apes such as chimpanzees or orangutans in his book “Of the Origin and Progress of Language”: “The orangutan is an animal of the human form, inside as well as outside: That he has the human intelligence, as much as can be expected in an animal living without civility or arts: That he has a disposition of mind, mild, docile and human:

That he has the sentiments and affections peculiar to our species” (Monboddo, 1774, p. 289).

Interestingly, such writings impacted scientific theories as well as popular thoughts, starting to influence the theatrical art (see Figure1) and the poetic literature of the 18^th and 19^th centuries (E. Darwin, 1803).

Figure 1: Illustration of Mazurier’s ape costume for his role of Joko at the Theatre de la

Emerging in the early 19^th, the first comprehensive theory of evolution known as Lamarckism as well as Transformationism emphasized the importance of environmental adaptation in species complexity. In fact, even if Jean-Baptiste Lamarck in his theory of the transmutation of species believed in spontaneous generation and then, rejected the idea of a common ancestor (Lamarck, 1809), his concept of inheritance of acquired characteristics in species strongly influenced evolutionary thinkers. Professor in zoology, Lamarck famously illustrated his theory using the giraffe’s neck adaptation as one example (see Figure 2) in his books of 1802 and then 1809: “In regard to habits, it is interesting to observe a product of them in the particular form and height of the giraffe. […] the earth is nearly always arid and without herbage, obliging it to browse on the leaves of trees and to continually strive to reach up to them. It was resulted from this habit, maintained for a long time by all individuals of the race that the forelegs have become longer than the hind legs and its necks has so lengthened itself” (Lamarck, 1809, p. 219).

Figure 2: Drawing by Lamarck depicting the giraffe’s neck adaptation. He suggested that, over generations the long neck of the giraffe evolved to reach higher leaves, which are unattainable by any other herbivore. (Lamarck, 1802)^.

Hence, in response to modifications in their environment, a given species adopted new habits leading to new structures (e.g. muscles) accumulated across the future generations and resulting at some point in a new species. Despite the fact that Lamarck’s theory was well conceptualized, he did not explain explicitly how the acquired characters were

transmitted within the next generation. Nevertheless, even if he never pronounced the word

“heredity”, Lamarck yet referred to sexual reproduction and shared characters between both parents (Burkhardt, 2013).

The main opponent to the theory of transmutation of species was George Cuvier, who believed like Aristotle at this time in the fixity of species. According to him, a species could only change after an extinction or a catastrophic episode leading to a new period of creation. Cuvier’s theory came from his work as a palaeontologist, for which he is often considered the funder of the discipline as well as that of comparative anatomy (Bowler, 2003).

Nowadays, some researchers still claim a Lamarckism point of view in modern fields such as developmental plasticity or epigenetic inheritance, mainly focusing on the developmental aspect of Lamarck’s theory (Gissis et al., 2011).

From the Antiquity with Anaximander of Miletus to the early 19^th century with Jean–

Baptiste Lamarck, many concepts of Darwin’s theory were already claimed. Nevertheless, the “Darwinian revolution” (Burkhardt, 2013) enabled for the first time the conceptualization of all relevant hypotheses in one comprehensive theory that is currently the base of a modern view of evolution.

2.1.1.2. Darwinism & Modern view of Evolution

Travelling across the globe aboard to the HMS Beagle during five years, the young naturalist Charles Darwin collected fossils and geological artifacts, while precisely describing his surrounding environment. Writing his discoveries on a personal notebook

“The voyage of the Beagle”, Darwin started to question the fixity of species, encouraged by the Captain of the HMS Beagle, Robert Fitzroy, who gave him the first volume of

“Principles of Geology” wrote by Charles Lyell, a famous geologist of his time, supporting the idea of slow and long periods of modifications for the development of earth, totally rejecting the theory of George Cuvier. Influenced by his observations and Lyell’s ideas, Darwin secretly modelled the concept of transmutation of species that he described in opposition to Lamarck as a process of divergence and branching between species. While Darwin already built the foundations of his concept of natural selection, named so in opposite to artificial selection made by humans (Huxley, 1881), at the time of his travels (see

Figure 3: Illustration of Darwin’ Finches, observed in Galapagos Island (1835). Darwin described his concept of natural selection using the evolutionary mechanisms that were at play in Finches.

According to Darwin, the different species of Finches have different beaks because they are adapted to eat different kinds of food (e.g. nuts, insects) but they all descend from of a common ancestor due to their important behavioural and anatomical similarities.

In parallel to Darwin, Alfred Russel Wallace, a naturalist, also believed in the transmutation of species after his own observations in South America and Malay Archipelago. He also suggested in his early writings that the evolution of species, would be explain by branching mechanisms (Pallen, 2011). Like Darwin, Wallace was strongly influenced by a clergyman, Thomas Robert Malthus and his concept of “struggle for existence” (Bowler, 2003). Advised by Lyell and Joseph Dalton Hooker, Darwin allowed them to present conjointly his own work on natural selection as well as Wallace theory to the Linnean Society in 1858 (Wyhe &

Rookmaaker, 2012). Yet, one year later, the Darwinian revolution was fully realized after the first publication of Darwin’s famous book “On the Origin of Species” (Darwin, 1859).

Darwin’s theory on natural selection and branching always provoked intense debates in the scientific community of the 19th century. In fact, the concept of branching claimed by Darwin suggested that humans and other great apes were together on the same evolutionary tree. Triggering a philosophical revolution, scientists such as Cuvier or even Darwin’

friends Lyell and Wallace questioned its perspective. Indeed, in Cuvier’s theory, humans are from a different order of mammals and thus, cannot be compared to any other species.

Similarly, Lyell and Wallace effectively defended the idea of a physical ancestor between humans and other great apes but totally disproved the continuity between some aspects of their minds.

The debate became even more intense with the successive publications of “The Descent of Man and Selection in Relation to Sex” (Darwin, 1871) and “The Expression of Emotions in Man and Animals” (Darwin, 1872) in which Darwin clearly compared humans to other

animals from a biological point of view to an intellectual and emotional one. Read by the non-scientific community as well, the news-papers of its period often caricatured Darwin as a primitive monkey (see Figure 4). Nevertheless, its caricatures finally contributed to the popularity of Darwin in evolutionary theories.

Figure 4: Darwin caricatures in 19^th century’ new papers (Cavin & Vallotton, 2009)

Moreover, Thomas Henry Huxley, positioning himself as “Darwin Bulldog”, defended against old odds Darwin’s hypotheses in demonstrating for instance, how humans and apes were close anatomically speaking, even in their brain structures. He also pointed out the fact that, in opposite to Lamarck’s or Cuvier’s theories, Darwin was the first to describe evolutionary mechanisms without any divine or supernatural intervention. Visionary, Huxley concluded in his book “On the Origin of Species: Or, The Causes of the Phenomena of Organic Nature”: “Mr. Darwin’s work is the greatest contribution which has been made to biological science […] and I believe that, if you take it as the embodiment of a hypothesis, it is destined to be the guide of a biological and psychological speculation for the next three or four generations.” (Huxley, 1881, p. 144).

As Huxley predicted, nowadays, Darwinian theories of evolution are strongly supported by the emerging cross-disciplinary consensus of the early 20^th and 21^st centuries (see Figure 5).

His grandson, Julian Huxley, also biologist, was the first to name this consensus “the modern synthesis of evolution” (Huxley, 1942).

Figure 5: Diagram of the idea brought together in the “Modern Synthesis” in evolutionary biology (modified from Ian, 2020).

Therefore, influencing scientists and thinkers from the 19^th to the 21^st centuries, Darwinian theories were the keystones of evolutionary thought. Darwin indeed initiated a philosophical revolution in which other animals, like humans, expressed and felt emotions.

Section 2.1.2. will develop how this perspective influences current theories of emotion.

2.1.2. Evolution in Theories of Emotion

The definition of emotion may be one of the most debated concepts in research. Despite the fact that the lack of consensus led few psychologists to even doubt of the necessity of a definition (Frijda, 2007; LeDoux, 2012), we will consider in the next sections that “emotion”

is a rapid process, focused on a specific event and involving i) elicitation mechanisms based on stimuli relevance; and ii) multiple emotional response processes (action tendency, autonomic reaction, expression and feeling components - Sander, 2013).

While the definition of emotion is still discussed, its evolutionary basis is now recognized by most scientists in the affective domain. From the theories of Nesse to Frijda, Ekman or more recently Scherer’s model, evolution is key to understand the genesis of emotions in humans. Moreover, if old evolutionary mechanisms are really at play in our emotional experiences, we can assume that emotional processes are also present in other animals, especially in phylogenetically close species such as non-human primates. In spite of intense debates on this last perspective, research however often described the existence of more or less complex affective lives in multiple species across the animal kingdom.

2.1.2.1. Evolution of Emotion

Darwin in “The expression of the emotions in man and animals” (Darwin, 1872) was the first to truly emphasize the key role of evolutionary mechanisms in emotional processing.

Nowadays, it is accepted that emotions have an evolutionary history. Randolph Nesse, for example, writes in 2009 that “Natural selection shaped emotions and the mechanisms that regulate them” (Nesse, 2009, p. 159), referring to the role of natural selection in first, the subdivision of emotional types, and second, in the organization of psychological and physiological processes that facilitate an adaptive response to a particular situation (Al-Shawaf & Lewis, 2017; Nesse, 1990 - see Figure 6). In fact, different emotions were probably shaped by natural selection because each specific situation elicited different sets of adaptive responses. However, in our modern environment, emotions are not always adapted (Greenberg, 2002). Johan Bolhuis and Clive Wynne explained this, with a practical and quite comical example: “The tendency of modern humans to spontaneously fear spiders rather than cars, which are far more dangerous, is thought to stem form the prevalence of poisonous arachnids, rather than dangerous driving, during the Pleistocene.” (Bolhuis & Wynne, 2009, p. 832). Yet, emotions enable to react differently to a threatening or a joyful situation for instance. This last process was well conceptualized by Nico Frijda with his notion of action readiness, referring to motivational aspect of emotions (Frijda, 2007, 2016). In fact, specific motives would appear to “move” animals to achieve their biosocial goals (e.g. reproduction) and to guide them to pay attention or be emotionally aroused in a certain situation (Gilbert, 2015).

Thus, most emotions may involve a position toward a specific object (e.g. rejection) and readiness to implement that position in action (e.g. by moving away). Furthermore, states of action readiness would involve activation and deactivation states as well as action tendency (theorized by Arnold, 1960) to avoid or approach an object in a peculiar context. Action tendency relies on specific brain networks in the human brain involving bilateral prefrontal cortex (PFC), amygdala-motor pathway, right inferior frontal gyrus (IFG), anterior cingulate cortex (ACC), periaqueductal grey area (PAG) and basal ganglia (See Section 2.2.1.1 for a more detailed description of neural networks involved in emotion in humans and Section 2.2.2.2 for a review in non-human primates). Moreover, in his concept of approach-withdrawal, Richard Davidson demonstrated the distinct involvement of the right and left PFC depending on approach or avoidance behaviours elicited by the type of emotion (Davidson et al., 1990). Davidson and collaborators indeed demonstrated a stronger

activation of anterior fronto-temporal regions in the right hemisphere for fear and disgust faces (withdrawal emotions) compared to higher neural activity in the left hemisphere for happy faces normally triggering approach behaviours (Davidson et al., 1990; Davidson, 1992).

Figure 6: Phylogeny of emotions shaped by natural selection. Resources are represented in upright font, emotions in italic and situations in capitals. Natural selection gradually differentiated responses to increase the ability of individuals to obtain the three main types of resources: personal, reproductive and social effort. Emotions were thus shaped to deal with situations arising from the pursuit of specific goals (Nesse, 2004).

As illustrated in Figure 6, different situations can have adaptive challenges in common.

Consequently, emotions can be classified using two dimensional aspects with i) arousal and ii) valence (Nesse, 2009). “Arousal” refers to a short-term increase in some processes that can be viewed as involving excitatory mechanisms (increase in behaviour or physiological activity) (Fowles, 2009). For instance, a massive increase in sympathetic nervous system (e.g.

cardiac or respiratory rhythm) triggered by a phobic stimulus (e.g. spider). “Valence” refers to the pleasant or unpleasant characters of emotions (e.g. Frijda, 1987; Scherer, 2003). For example, happiness is classified as a positive emotion whereas threat is recognized as a negative one. Positive emotions should elicit approach behaviours whereas negative emotions should trigger avoidance behaviours.

These two dimensions are highly correlated and thus, both are often used for the modelling of emotions (starting from Russell, 1980). Nevertheless, other dimensional aspects exist to represent emotional experiences (Fontaine et al., 2007). In fact, the individual sense of power

or control to represent emotions (potency – control) was also well described in the literature.

For example, anger is expected to score highly in this dimension whereas fear is expected to score extremely low (Goudbeek & Scherer, 2010). Interestingly, Fontaine and collaborators highlighted as well the importance of a fourth dimension in the representation of emotions.

This last dimension, characterized by the unpredictability of an emotional event, would be indeed particularly essential to explain the ambivalent status of surprise (Fontaine et al., 2007).

Moreover, most of the theories of emotions involve complex psychological and physiological processes as well as evolutionary mechanisms (Sander et al., 2018). For instance, Paul Ekman and David Matsumoto define emotions as “Transient, bio-psychosocial reactions designed to aid individuals in adapting to and coping with events that have implications for survival and well-being” (Ekman & Matsumoto, 2009, p. 69). Hence, their definition highlights the key role of emotions in psychological and physiological processes enabling to maximize the chance of survival of an individual. Furthermore, Ekman in his theory of Basic emotions (Ekman, 1999), underlines the existence of an “Emotion alert database” storing schemas information and enabling individuals to react adaptively. He gives as an example the perception of a coiled object that could match with the schema of snake and thus trigger the emotion of fear. Importantly, he also emphasizes that the universality of seven emotional expressions relies on brain regions such as the amygdala and the insula (Sander et al., 2018) for anger, disgust, fear, happiness, sadness, contempt and surprise (see Figure 7), suggesting inherited mechanisms from our evolutionary history (Ekman, 2003). For instance, happiness would correspond to sub-goals being achieved, anger to an active plan being obstructed, sadness to the failure of a major plan or loss of an active goal, fear to self-preservation goal being threatened or goal conflict and disgust to gustatory goal violated (Juslin & Laukka, 2003). Yet, the universality of emotions is controversial in the literature.

Some findings indeed demonstrate cross-cultural emotional basis (e.g. Sauter et al., 2010;

Scherer et al., 2001) whereas others do not (e.g. Crivelli et al., 2016; Jack et al., 2016). Despite the fact that the results found by Carlos Crivelli and collaborators on cultural variation of emotional expression are highly debated (Kret & Straffon, 2018), other findings on facial expressions of emotions also suggest cross-cultural differences. According to Jack and collaborators, Ekman’s work was indeed biased by the use of static images excluding the temporal dynamic of facial expression for instance (Jack et al., 2014). The authors decided thus to investigate across three different studies, the conceptual mapping, the dynamics and