A Study on Human Evolution and How Humans are Able to Detect Animals

It is widely theorized that, throughout the longitudinal evolutionary history as hunter-gatherers, the human species developed sophisticated mechanisms of animal detection. One of these mechanisms geared towards animal detection is so called “kin recognition,” by which various species of animals, including the human species, respond more quickly and adroitly to the traces of other animals that are phylogenetically closer to themselves. It is also dealt with, in this study, how the human species developed a way to respond differently to different developmental stages of animals, based on the postulate that this ability is an essential part of the hunter-gatherer life.

In order to test these hypotheses, we had 24 participants exposed to 100 unique images, 50 of which are with animals inside the scenery, and the rest with animals digitally removed from the scenery, or extracted from different, empty parts of the same scenery. The participants were asked to use the index and middle fingers of their dominant hand in order to discern whether or not there was an animal or a human being present in an image that flashed through their sight in the computer screen.

As the result, it turned out that, when it comes to reaction time of the responses, the presence of animals was a significant factor, along with the phylogenetic distance of an animal inside an image.

There were also interactions between the presence of animals and the phylogenetic distance, and between the age of an animal and its phylogenetic distance from the human species. The interactions also existed when it comes to accuracy of the responses, mainly between the presence of animals and their phylogenetic distances from the human species, and between the age of an animal and its phylogenetic distance.

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It is widely theorized that, throughout the longitudinal evolutionary history as hunter-gatherers, the human species developed sophisticated mechanisms of animal detection. For the hunter-gatherer life, very few things were more important than detecting the right kinds of animals one would face in the individual’s daily life, and the usual relationship an animal poses with a human being was probably the most crucial factor that led to the effectiveness of the detection.

In this vein, detecting the right kind of animals that are phylogenetically closer to oneself in the right circumstances was of special importance, as this is clear not only from the evolutionary traces of the human species, but from the evolutionary traces of various other animal species around the planet – for this mechanism was coined the term “kin recognition.” (“Social behaviour, animal,” 2012) The three ways in which this “kin recognition” mainly works are the use of environmental cues, prior experience, and phenotype matching. Since this is the case, it might be hypothesized that this evolutionary trace of kin recognition is still prevalent in the modern human species, which means that human beings will be still equipped with the mechanism of kin recognition geared towards the right implementation of how they detect animals.

To be more precise with our postulate, it might be hypothesized that human beings respond more adroitly when detecting their own species, or other sorts of primates. Detecting other sorts of mammals will come the next, while it might be hypothesized that human beings respond less adroitly when detecting the rest.

Yet, it might be hypothesized, based on previous studies, that there is an exception to our postulate that phylogenetically farther species of animals from human beings will be detected less adroitly by the human species – snakes. According to a study conducted by Anders Flykt and Roberto Caldara in the University of Geneva, it was shown that human participants with ophidiophobia or arachnophobia clearly had shorter reaction times when they were exposed to images of snakes or spiders, respectively. It has been also postulated in this study that this phenomenon might be based on the evolutionary psychology of how the human species has evolved.

Therefore, it can be further hypothesized on our part, that snakes, despite their reptilian categorization that is phylogenetically distant from the mammalian human species, still might generate shorter spans of reaction time from human detectors, which means that snakes are potentially an exception to our previous postulate regarding the mechanism of kin recognition.

It might be also postulated that the way how the human species evolved their own animal detection involves the ability to discern the different developmental stages of animals. After all, in nature, the developmental stage of an animal is an important factor when it comes to the animal’s relationship between a human hunter-gatherer, since this may even discriminate whether the same species of an animal might be a predator against, or fall prey to a human being. Thus, it might be also postulated that there will be significant differences in how a human detector copes with detecting an infant animal of a certain species, and with detecting an adult animal of the exactly same species.

All 24 participants in this experiment were recruited from Vassar College campus. 10 of them were recruited from Psychology 100 in Vassar College’s psychology department, while the rest of the participants were recruited voluntarily through the introduction by the student researchers. Yet, it has to noted, nonetheless, there existed a restricted age bias among our participants, as most of them were within the age of 18-23, which may pose a threat to our external validity.

For the experiment, we had 100 unique images handy, mainly from the web. Among these images, 50 of them had animals inside the scenery, while the other 50 had animals digitally removed from the scenery or were based on different parts of the scenery. The experiment was decided to be computer-based, so we had a personal computer handy inside the room where our experiment would be held. Participants were asked to be seated 70 cm from a computer screen.

The experiment for one participant consisted of three different sessions with 100 trials for each. In order to make certain that participants are prompted to focus on the stimuli, we had a fixation cross appearing in the screen for the beginning of every single trial. The fixation cross will last in the screen for 1 second. Then after a second with the fixation cross, there would appear a target image, either with or without an animal inside its scenery, for 20 milliseconds.

After the target image flashed through, participants would be presented with a black screen, and asked to use either the index (“b” key in the qwerty typing system) or middle (“n” key in the qwerty typing system) finger of their dominant hand in order to answer whether or not there existed an animal inside the target image that had just flashed through. After a participant responded, the black screen would remain for 500 milliseconds, and a new trial would begin afterwards. Participants would be informed in advance that 50% of the images contain animals while the other 50% of the images do not. In each session, the order of images will be presented in random order.

In order to account for the dominance of the index finger over the middle finger, we divided participants into two groups: those who will use the index finger (“b” key in the qwerty typing system) to indicate that an animal or human exists inside the image, and those who will use the middle finger (“n” key in the qwerty typing system) to indicate that an animal or human exists inside the image.

When it comes to the mean accuracy of the responses, the presence of an animal inside an image seemed to be insignificant as a factor for our experiment. F(1,23) = 2.00, n2 = 0.080. The same was the case with the developmental stage of the animal. F(1,23) = 2.34, n2 = 0.092. The same was the case with the animal’s phylogenetic distance from the human species, as well. F(4,20) 1.98, n2 = 0.284.

Nonetheless, there were significant interactions when it comes to the mean accuracy of the responses, such as the interaction between the presence of an animal and the animal’s phylogenetic distance from the human species, F(4,20) = 7.41, n2 = 0.597, the interaction between the age of the animal and its phylogenetic distance, F(4,20) = 12.82, n2 = 0.719, and the interaction among all the three independent variables in the study. F(4,20) = 3.67, n2 = 0.423.

For all the levels of independent variables, the reaction time of the responses did not follow normal distribution, without any single exception. In addition, for all the levels of independent variables, all the results from the reaction time of the responses were positively skewed. The conjectures on how this propensity took place will be discussed in the following section.

According to a study conducted by Joshua New, Leda Cosmides, and John Tooby, animals cause a stronger recruitment of attention from human beings, since this sort of animal detection is adaptive in human evolution, as much as animals are the category of objects that offers the most time-sensitive threats or opportunities towards human beings.

In this vein, our current experiment can be said to have supported this idea of how the ability of animal detection has been a part of the human evolution, since the results have shown that the presence of an animal, even inside a computer-based image, did bring a significant difference in how quickly a human participant could respond to the task in our experiment as in accordance with the stimulus.

In addition, the result that, for all the levels of independent variables, the reaction time of the responses from human participants clearly showed positive skewness instead of normal distribution is also significant in its own: This result shows that, regardless of any level of the independent variables given to each of their trial, human participants always had inclination to respond more quickly during the performance of their task, as long as the goal of the task was to search for an animal. This is a strong buttress for our postulate that the ability of animal detection has been a part of longitudinal human evolution.

Yet, as shown in Figure 1, there were some exceptional cases in which the details of our prediction did not exactly match the real data acquired from the experiment. For instance, when the animal inside an image was an infant, strangely, reaction time of the responses tended to be shorter for non-primate mammals than for human stimuli or primates. This cannot be explained alone by our postulate of kin recognition as a part of how the human ability of animal detection has evolved, because non-primate mammals are phylogenetically more distant.

Yet, when we say that kin recognition has been a part of how how the human ability of animal detection has evolved, we should not forget that, as previously mentioned, this human ability of animal detection has to do with how animals were the most time-sensitive threats or opportunities to early human hunter- gatherers. (New et al, 2007) To be straightforward, when analyzing how human beings detect different sorts of animals, it is crucial to conjecture in the perspective of a primitive human hunter.

In the pre-historical world, it was mostly non-primate mammals that used to be preyed by human hunters, while infants among this group were considered the best prey in the perspective of an early human hunter. In fact, even in the more civilized, historical world of the 21st century, it is a definite propensity among the human society to slaughter livestocks for meat when they are in the very early period of their developmental stage. This is clearly shown in how cattles for meat are mostly slaughtered and processed (86.1% of them) when they are 24~28 months of age, while only 1.2% of the cattles are slaughtered after they reached more than 31 months of age.

In addition, among the human societies worldwide, cannibalism has been tabooed by the majority of human beings, which dates back to the pre-historical era, mainly upon certain biological reasons. In this broad context, when we conjecture in the perspective of early human hunters who have begun to evolve the more complex ability of animal detection, it is natural that this ability, upon its development, was geared towards the detection of infant mammals, which were considered the best prey in the primitive human perspective, while there was less incentive for this new ability of animal detection to be geared towards other infant human beings.

This is also in accordance with our data for reaction time, in which, the different developmental stages of an animal themselves did not turn out to be significant as a factor, yet did turn out to be a significant factor only when inside the interaction with the animal’s phylogenetic distance from the human species.

It also should be noted, as shown in Figure 2, that control groups (baselines) for the images that used to have human beings inside it tended to result in faster responses, while for both developmental stages of the animals, the images with human beings resulted in slower responses than those with other primates. This is also not strictly in accordance with our postulate of kin recognition alone. Yet, when we conjecture in broader context, especially regarding the subtle differences between the images with human beings and those with other primates, this might be explained in accordance with the theme of “detection”.

According to a psychological study conducted by Ulas Basar Gezgin, human beings, throughout their evolution, also tend to have evolved a psychological stimulus towards architectural objects. (Gezgin, 2013) Meanwhile, in our experiment, in contrast to the images with primates that usually consisted only of natural vegetations, there existed some images in which human beings were accompanied by architectural objects in the background. This must have caused a confound, in which our human participants also engaged their detection of architectural objects additionally to their performance, which resulted in faster responses to the images that also tended to have architectural objects inside the scenery.

In addition, when it comes to their task for detecting human beings inside the images, those architectural objects being detected in the same scenery might have distracted our participants from their original task of detecting humans, finally resulting in slower responses. This explanation is also in accordance with the pattern in Figure 3, in which the accuracy of responses for finding human beings turned out to be lower than their counterparts for the baseline images.

It was completely against one of our previous postulates that human evolution must have developed a mechanism to detect snakes in particular, since the data from our experiment showed the opposite result, in which reaction time for snakes was significantly slower, not faster, than that for other kinds of animals. Yet, it must be questioned, at this point, whether our postulate and the primary literature on which this postuated was based, were really valid in the first place. In fact, the study conducted by Anders Flykt and Roberto Caldara has a fatal flaw that the sample of its subjects was very disproportionate, as all of the subjects were either ophidiophobic or arachnophobic in the first place.

Concluding that ophidiophobia is a part of human evolution, upon this disproportionate sample, is to commit generalization through the fallacy of composition. (Kelley, 2013) There is also a study which states that about a third of adult humans are ophidiophobic, and that this is the most commonly reported phobia, (Isbell, 2009) yet to have this numerical statement as a “proof” for claiming that ophidiophobia is a part of the human evolution, without real experimental data handy, is to commit the fallacy of appeal to majority.

In addition, this fallacy is also accompanied by ourselves falling into the oblivion of the fact that there can be other alternative hypotheses out there (Kelley, 2013) to explain this phenomenon of ophidiophobia, and there is a chance that ophidiophobia is not related to our current theme of how animal detection was evolved within human beings. In addition, we have another reason to conclude, at this point, that our current theme of animal detection and phylogenetic distance is not related to the phenomenon of ophidiophobia, since, in another angle, the data that snakes resulted in slower responses from human participants actually go hand in hand in our postulate regarding the development of kin recognition.

The best answer for our discussion regarding snakes might be in the same vein with the fact that snakes have physical shapes that are very different from their counterparts in other vertebrates. In fact, the interaction between the presence of an animal and the animal’s phylogenetic distance from the human species, as in our data for the accuracy of responses, might be also due to this problem that snakes lack limbs and distinct torso, hence their ability to camouflage inside the scenery and the difficulty on our part to clearly detect them.