The Evolution of Attention
Consciousness can be understood when knowing the Evolution of Attention from the first multicellular lifeforms to modern mammals. When did our ancestors first experience consciousness?
This is an excerpt from the book series Philosophy for Heroes: Act. You can preorder the e-book here.
Attention Attention is the brain’s process of limiting alternative thought patterns, then increasing the most dominant thought pattern’s strength. It is like a simple majority rule: the most successful thought pattern gets all the resources while other thought patterns are suppressed. While we can jump back and forth between different thoughts, we cannot have two dominant thought patterns at the same time.
Attention refers to the ability to select between competing or even contradicting sense data. For example, you hear something on your left, see something moving on your right, you are hungry, and tired; which sense data gets your attention first? The brain parts involved that help us make such a decision underwent half a billion years of evolution and can be traced back to simple multi-cellular organisms [Kaas, 2017, p. 547–554].
To gain a better understanding of our evolution, the best way is to draw its history as a tree, with branches representing the creation of new major species. As we are looking only at the evolution of attention, our focus will be a small selection of species rather than a comprehensive discussion. Figure 5.2 shows the evolutionary timeline of primates with different species branching off, Figure 5.3 shows the same tree of dependencies in a graphical form.
|600 mya||sponges||calcium signalling|
|580 mya||Hydras||basic nerve net|
|550 mya||arthropods||information classification|
|535 mya||lancelets||olfactory system|
|520 mya||fish||optic tectum (information tracking)|
|520 mya||fish||thalamus (information integration)|
|520 mya||fish||basal ganglia (resolving conflicts)|
|520 mya||fish||amygdala (information evaluation)|
|520 mya||fish||hippocampus (spatiotemporal memory)|
|450 mya||sharks||cerebellum (movement programs)|
|300 mya||reptilians||wulst (high-level planning)|
|225 mya||mammals||neocortex (similar to wulst)|
|55 mya||primates||prefrontal cortex|
|Figure 5.2:||Timeline (in million years ago) of the evolution of attention in animals with a list of species that branched off the evolutionary tree and the brain part that first appeared at that time.|
|Figure 5.3:||Simplified evolution of attention in animals.|
Over this long history, the brain became a collection of different functions, layered on top of each other, with many systems having overlapping responsibilities. If a neural pathway helped one of your ancestors to avoid danger, that pathway survived, even if that meant that the architecture became somewhat chaotic (“complex”). Nature does not care about an easy-to-understand architecture; it cares only about what works and what does not. Sometimes, the organization of a certain function into clearly distinct brain parts had an evolutionary advantage (for example, separating the neocortex from the rest of the brain). In other cases, the most efficient layout was having one function directly beside the other (for example, the different brain regions within the necortex). Yet, for our understanding of the brain, it is sufficient to look at it as a system of separate parts interacting with each other. We just have to keep in mind that the functions of brain parts usually blend into those of neighboring brain parts, and that there are many more interactions and connections between brain parts than listed here.
How do milestones in the evolution of the brain contribute to our conscious experience and decision-making? How did something like the brain, which can respond to and focus on sense data, evolve?
5.1.1 Nerve Nets in Hydras
Looking at our tree of animal ancestors (see Figure 5.3) in regard to brain development, sponges were the first to settle in an evolutionary niche (more than 600 million years ago). They are sea animals that are mostly immobile and simply filter oxygen and nutrients from the ocean water. Although they have a primitive way of pushing water, when it is toxic or otherwise polluted, out of their bodies, they lack any form of nervous system as we understand it. Their cells communicate directly with each other using calcium signalling. Each cell contains a concentration of calcium that can be released if it receives calcium from neighboring cells. This way, it creates a calcium wave propagating throughout the organism. You can imagine it like having many square containers grouped together and filled up to the brink with water. When you take one container and pour it into its neighboring containers, all the containers will overflow.
The first animals with some semblance of a brain were Hydras. They branched off our evolutionary tree more than 580 million years ago. They are small (around 10 millimeters in length) animals that usually attach themselves to the surface of an object in their environment and can slowly move over it or detach themselves and float in the water. They have a basic nervous system that allows them to use their tentacles to attack prey. If another animal (mostly tiny planktonic crustaceans like Daphnia or Cyclops up to five millimeters in length) touches a tentacle, the nerve cells activate the tentacle to take it into the Hydra’s mouth. There is no central nervous system that organizes this activation. Instead, nerve cells are spread throughout the body of the Hydra in a nerve net. This enables the Hydra to respond to its environment without being able to detect where this original stimulus came from. Any signal leads to the same reaction, for example, all muscles contract at the same time.
If the human body had a nerve net instead of a nervous system and brain, we would not be able to figure out where we were touched, only that we felt something and as a result had to come up with a general response to this touch. Such a general response is comparable to our hormonal system: for example, the adrenaline released in a situation of danger does not cause specific actions but prepares the whole body for a possible injury or energy exertion. Another example would be the regulation of body temperature which, again, is a general response to certain conditions instead of a specific movement.
5.1.2 Classification of Signals in Arthropods
A basic form of attention appeared at the time the arthropods (insects, spiders, crabs, etc.) split off the evolutionary tree around 550 million years ago. With this new form of attention, instead of treating all sensory input as equal, the information is pre-processed and can thus be amplified and classified. For example, imagine noticing something suddenly moving in the grass—it immediately draws your attention. Once you see it emerging from the grass, you classify it as a particular concept, for example a snake.
|Dog at 1pm||Dog at 2pm||Analysis|
|Basket||Basket||Dog has not moved|
|Rug||Rug||Dog has not moved|
|Basket||Rug||Dog has moved|
|Rug||Basket||Dog has moved|
|Figure 5.4:||If the dog is at different places at 1pm and 2pm, we can conclude that the dog has moved.|
At its core, classification is about filtering information we do not need. No longer would every signal cause a reaction. Instead, the organism was able to focus on specific signals and react to those. Most multi-layered nervous systems (including our own) support this kind of filtering. By comparing several images on your retina for changes, your visual system can make out which moving part belongs to which previously seen part. For example, if your visual system identifies a dog and then the same dog in subsequent images, you perceive any changes in those images as movements of the dog. If you closed your eyes every second, you would perceive the dog “jumping” from place to place. You would have to use your short-term memory as a workaround and remember where the dog was earlier to decide whether or not he had moved. Figure 5.4 shows an example that represents the filter function XOR. When passing two images through such an XOR filter, it would highlight changes between both images and thus detect movement.
Visual pre-processing is done partly by the retina of our eyes, detecting edges and changes, and compressing the data-stream toward the rest of the visual system. To understand what is happening, imagine looking at a picture of a tree in front of a white background. The brain perceives the detailed raw image, then the visual system extracts the edges of objects to identify them (see Figure 5.5). This way, the brain can determine that there is the shape of a tree. This is the opposite of what happens when drawing a picture: we start out with the tree in mind, then draw the edges and contours and then finally fill them in with details.
|Figure 5.5:||Edge detection applied to a photograph (image source: John McLoone, 2010).|
Beyond being just a one-way street of information (classifying the image data to abstract information), classification systems can also help you to direct attention. When we see things that are new or unusual, our brain allocates resources to finding out what they are. This could be just by turning our head, refocusing our eyes, looking at things from a different perspective, going closer, or asking others about the new or unusual things.
5.1.3 The Olfactory System in Lancelets
The olfactory system was probably one of the earliest sense organs that evolved in animals, as detecting molecules is closely connected to a lifeform’s search for nutrients. While not directly related to us (they diverged from our ancestors around 535 million years ago), we share some of our olfactory-related genes with lancelets (see Figure 5.6). They can be seen as predecessors of fish with similar organs but in more primitive form. For example, their gill-slits are used for feeding but not for respiration. Likewise, their circulatory system transports nutrients but not oxygen. While they have no centralized olfactory system (we humans do), their olfactory receptors are studded along their flanks to detect possible sources of nutrition in their aquatic environment.
|Figure 5.6:||Lancelets can be seen as predecessors of fish with similar but more primitive organs (image source: Shutterstock).|
Molecules connect to the olfactory system over the peripheral olfactory system. In aquatic animals this happens directly via contact with the water. In land animals with lungs this happens by having the airborne molecules dissolve into mucus on top of the olfactory receptor cells. If the molecule binds with the receptor cell, a nerve signal is created and transmitted to the brain. A peculiarity of our sense of smell is that it is the only sense that can bypass the thalamus (see Chapter 5.1.5) and send signals directly into the neocortex.
While our sense of smell might seem to play little to no role in our modern hectic life, it actually has a significant impact. In combination with our sweat, our sense of smell can communicate emotions. Usually, we think of emotions being contagious by way of our sense of sight or sense of hearing, but studies have shown that they are also contagious with our sense of smell. This works even when the smell is separate from the person (for example, on their clothes). So, even without words or gestures, people can communicate their distress to others nearby Mujica-Parodi et al. . The evolutionary advantage of this mechanism makes sense, especially when it comes to fear. Putting yourself into a heightened state of alertness when detecting fear in other people can increase your chances for survival.
The olfactory system also supports mate selection by detecting pheromones which contain the MHC complex. In Philosophy for Heroes: Continuum , we discussed the relevancy of the MHC complex in the immune system’s ability to differentiate self with other. In mate selection, a similar system is used to find a partner that is genetically not too similar but also not too different. The evolutionary advantage is to have a compatible partner with increased resistance to infectious diseases by providing a variability in the MHC complex [Ejsmond et al., 2014]. At the same time, it reduces the chance for children to inherit genetic diseases. Similar to the immune system, the olfactory system probably becomes accustomed to the MHC complex of relatives in early childhood. If this contact does not happen, there is no biochemical obstacle to falling in love with close relatives [Potts and Wakeland, 1993]. In that regard, Freud’s psychoanalysis (the Oedipus complex) was correct (as in: there is something like the Oedipus complex) but his explanation was not.
In terms of architecture, information travels not only in one direction, from the olfactory system to the brain, but also back from the neocortex to the olfactory system. We can experience this when we focus on smelling something, for example, checking whether food is still good. This focus can enhance the olfactory system and improve its efficiency by providing context information. In fact, the information from the millions of odor detectors in the olfactory system never even arrives at our neocortex. Instead, it is condensed into only 25 cells which are primed by the neocortex. If there is a strong smell, the sensitivity of the cells is reduced; if we want to pick up a faint smell, we can increase the sensitivity. If we smell something that could be peppermint, we reconfigure the cells to check for that particular smell, and so on. If a particular faint smell wins the neural competition, resources are allocated to enhance the sensitivity.
By combining the gustatory system (the basic tastes sensed by the tongue like salty, sour, bitter, umami, sweet, kokumi, calcium, and so on) with the smells detected by our nose, we can enhance our overall experience of food. Children learn to like or dislike certain types of food when observing what is safe for other people to eat [Elsaesser and Paysan, 2007]. While individual exceptions exist, if humans were genetically disposed to favor a particular food (like Koala bears prefer eucalyptus tree leaves) to the exclusion of other foods, our ancestors would have had a hard time spreading all over the globe.
If the olfactory system classifies something as inedible, it might initiate the gag reflex to protect the body from poisons. If we actually get food poisoning or an infection, the body reacts by increasing acetate levels in the blood. In the brain, this improves the ability to create memories. The evolutionary advantage of this pathway could be to better remember the situation that led to the food poisoning or infection and thus prevent it in the future. But the protection mechanism from food poisoning and infections is piggybacked by some substances. For example, alcohol is broken down into acetate in the liver [Lewis and Vander Heiden, 2016]. While alcohol consumption (especially binge drinking) is generally associated with memory loss, this chemical pathway shows that drinking moderate amounts of alcohol after a negative event actually makes you remember that event even better [Yoo et al., 2017]. This opens the door for a vicious cycle of alcohol addiction if it is used to raise one’s mood after a negative event, turning it into a downward spiral of becoming increasingly depressed. Vice versa, it also explains the social celebratory use of alcohol given that it is used for positive life events and strengthens memories of such events.
All these properties are reflected in the architecture of the olfactory system. There are the following connections (Figure 5.7):
- Trigeminal nerve, vagus nerve (gagging reflex, face muscles, expression of disgust);
- Hippocampus (spatial memory);
- Amgydala, hypothalamus (emotional reaction, hormones, pheromone processing);
- Neocortex (processing of smells);
- Hippothalamus (pheromones, hormones);
- Olfactory bulb (sensory cells); and
- Nose (air flow).
|Figure 5.7:||The architecture of the olfactory system.|
5.1.4 The Optic Tectum in Fish
Controlling eye movements made it necessary for fish (they split from the evolutionary tree around 520 million years ago) to develop central processing, namely the optic tectum. In mammals, this organ is called the superior colliculus and most of the processing has moved to the visual cortex. It helps fish (and us) to track moving objects and is responsible for blinking and pupillary and head-turning reflexes. The superior colliculus also receives auditory information to mentally move the location of a sound to the visual source, which can produce a ventriloquist effect: you are thinking that the puppet is the one speaking while the actual source of the sound is the ventriloquist himself. Similarly, the superior colliculus will make you think that the source of the sound is the television and not the loudspeakers.
In the brain, the superior colliculus sits right behind the optic chiasm where the nerves from the left and right eye cross. If you are not actively focused on something else, and an object moves outside your inner field of sight, this part of the brain is responsible for bringing it to your attention, after which you might move your head and re-focus your eyes to get a better picture of the possible threat. Imagine you did not have this reflex to see anything moving in your environment. The risk of injury (say, from an oncoming tiger) would be much higher because of your longer reaction time.
Superior colliculus The superior colliculus or optic tectum (in non-mammals) helps the eyes to track objects, and controls blinking, pupillary, and head-turning reflexes.
5.1.5 The Thalamus in Fish
The thalamus combines and pre-processes different sources of sensory information into a coherent whole before relaying it to other parts of the brain. On the evolutionary timeline, it also first appears in fish. In humans, an example for its ability to integrate information is the translation of the signals from the red, green, and blue cone cells in the retina into colors. While further processing takes place in the neocortex, the first part responsible for this color encoding is the lateral geniculate nucleus (or LGN). Another example is integration of visual and auditory signals. As visible movements and sounds are often correlated, the LGN can help to turn the eyes toward the moving entity using auditory information in addition to the sense data from the eyes [McAlonan et al., 2006]. It is also involved in a number of image pre-processing tasks. For example, it provides a three-dimensional model of the environment by combining the information from the left and right eyes.
Thalamus The thalamus integrates different sensory information and relays the information to other brain parts. For example, it combines sense data from the retina’s cones into colors, or calculates three-dimensional information from the two-dimensional images from both eyes.
Lateral geniculate nucleus The lateral geniculate nucleus (LGN) is part of the thalamus and relays information from the retina (via the optic chiasm) to the visual cortex. It pre-processes some of the information, for example, combining red, green, and blue photoreceptor cells into colors.
As an example, imagine seeing a barking dog. It is thanks to our thalamus that we recognize that the barking sound and the image of the dog belong to the same entity (or at least that we can turn our visual attention to the barking dog). Without the thalamus, we would perceive them as two separate events. For an example of when this fails us, imagine hearing a plane far above you: not taking into account the speed of sound, the distance between you and the plane, and the high speed of the airplane, your thalamus fails to combine the information correctly. You end up looking where you (falsely) expect the plane to be (where it had been a few moments earlier) instead of where it actually is. The neocortex could help out here of course, too. You could sit down and do mathematical calculations on paper to determine the actual position, considering the distance to the plane and the speed of sound.
But the thalamus is not just a relay station with some pre-processing going on. For example, the visual cortex uses the LGN to focus on particular aspects of an image and enhance it. While the LGN sits on the connection between the retinas and the visual cortex, it actually receives 95% of its input from sources other than the eyes, that is:
- The superior colliculus (tracking, eye movements);
- The visual cortex (creating a feedback loop with the LGN); and
- The midbrain and brainstem (pupillary light reflex, smooth pursuit, accommodation reflex, antinociception, REM sleep, preparation for fight and flight, arousal and sleep-wake cycle, attention and memory, behavioral flexibility, behavioral inhibition and psychological stress, cognitive control, emotions, neuroplasticity, posture, and balance, and sleep).
Given the high dependency on input from the visual cortex to process information in the LGN, when, for example, looking at an apple, that image does not necessarily arrive at the visual cortex in its original form. This shows that the LGN pre-processes everything coming from the eyes and is in a feedback loop with the visual cortex. Sense data does not just flow in one direction—bottom-up from the eyes to the visual cortex—there is also information that was already processed in the visual cortex flowing back into the LGN (also see Chapter 5.3.1).
5.1.6 The Basal Ganglia in Fish
The basal ganglia is thought to originate from the need to arbitrate between different courses of motor neuron activation. It identifies the “best” among several possibly contradicting courses of action. Rules determine what “best” means in a particular context. With the analogy of the neural committee, the motor program with the most votes from the committee gets selected to be executed.
Basal ganglia The basal ganglia is a part of the brain that arbitrates decisions by the neural committees. Also, it coordinates the sequence of entire motor programs. In both cases, it is not a decider but merely provides rules and structure, like a referee.
The basal ganglia is also involved in coordinating entire motor programs. Imagine an orchestra without a conductor: sure, the musicians could play their respective parts, but at different speeds and starting at different points in time. The basal ganglia is like a conductor of an orchestra, synchronizing the different motor programs, activating them in the right sequence and with the right timing.
5.1.7 The Amygdala in Fish
Yet another brain part, the amygdala, first appeared in fish. Arbitrating and catching our attention with the basal ganglia is one thing, how we prioritize the signal is another. While we can make decisions based on the strength of the signal—turning our head to the loudest noise seems to be a good strategy—we also need to put the signal into context. For example, instead of always running away from a tiger, we might consider whether or not to take the risk and first pick some berries and only then run away—especially if we are very hungry. This demonstrates how the amygdala uses information from a number of sources to prioritize different courses of action.
Amygdala The amygdala is the brain’s value center. Instead of relying on mere signal strength, the basal ganglia relies on the amygdala to evaluate different signals depending on the context. It is also connected to the hippothalamus providing a bridge to the hormonal system.
The amygdala is also connected to our hippothalamus, providing a bridge between the brain and the hormonal system. As such it can provide a fight, flight, freeze, or fawn response:
- Attack the predator (“fight” response);
- Run away from the predator (“flight” response);
- Stop moving (“freeze” response); or
- Submissive behavior (“fawn” response, by humans and other social animals).
How the fight and flight responses can help in a threatening situation is self-explanatory. The “freeze” response can work against predators because many predators’ instincts depend on motion. If their prey is not moving, the predator’s hunting instinct is not activated and they will look elsewhere for food. For example, cats take great interest in a moving toy while they might ignore something that stands still. Similarly, the “fawn” response works if the attacker is from the same species and also a social animal. Showing submissive behavior communicates to the other party that you are no threat, preventing injury for both parties.
Beyond helping with the execution of the immediate response (e.g., releasing adrenaline), it can also serve as an early basic form of memory. For the response to be effective, the hormonal changes caused by, for example, the flight response need to remain long after a predator has vanished from an animal’s view. It will cause it either to head home to a safe place or to be on alert when it returns to this location.
The information the amygdala is using is limited to immediately available sensory data. It activates emotional reactions based on mapping the input from the thalamus to emotional behavior. For example, the sight of fresh berries might evoke a positive emotional response while the sound of a rival might evoke a fight, flight, or fawn response. This response can overrule any rational evaluation of the situation because it is quicker and possibly stronger than signals coming from the neocortex. The amygdala associates sense data coming through the thalamus with positive or negative events and, ultimately, emotions, for example (Tye et al. , Rogan et al. , McKernan and Shinnick-Gallagher ): Tiger ⇒⇒ fear; apple ⇒⇒ appetite; and sun ⇒⇒ happiness. What makes this mechanism so powerful is that—while it requires very little processing power—it can cover a wide range of sensations.
5.1.8 The Hippocampus in Fish
A predecessor of our hippocampus also developed around the time of the first fishes. The actual hippocampus is unique to mammals but there are theories that similar structures evolved from a common ancestor of reptiles and mammals around 520 million years ago. Its main task is to create a mental map of an animal’s environment to allow the animal to remember where possible food and water sources are located. It also helps with navigation, remembering paths the animal has taken, relating spatially to other animals or objects, [Danjo et al., 2018] and recognizing places for orientation. A good example for the use of the hippocampus is squirrels burying nuts as food stashes for the winter. Our current understanding is that this map is not a literal map but instead makes heavy use of points of orientation. While many people can construct a mental image of a map, we tend to to orient ourselves by seeing something we know and then putting our goal in relation to the landmark. For example, when describing to another person the path to a location, we might say “Walk down the street until you get to the large tower, then turn right.”
Hippocampus The brain’s hippocampus provides us with a mental map for navigation. It also has a temporary component tracking, for example, which areas in our environment we have already foraged. The hippocampus together with the olfactory system (sense of smell) make up the allocortex.
While earlier animals could drift and react to sensory inputs (evading predators and approaching food), once the food was out of sight, it was also out of mind. The hippocampus allowed animals to find more food by avoiding areas that they had already foraged and exploring areas they had not foraged. This requires mapping the environment based on odors (the olfactory system has direct connections to the hippocampus) and sights, as well as prioritizing those according to the time they should be visited [Murray et al., 2018]. The hippocampus evolved to handle tasks in serial order with the right timing and in the right context. This stems from its ability to associate two memories with each other, which helps to find a path from one place to another [Samsonovich and Ascoli, 2005].
Did you know?
The hippocampus’ function becomes most visible during dreams, when experiences retained during the day are played back for long-term memory backup in the neocortex. While we cannot ask animals whether or not they dream, some animals show rapid eye movements (REM) in their sleep, pointing to an activation of their hippocampus. →→ Read more in Philosophy for Heroes: Epos [Lode, tba]
5.1.9 The Cerebellum in Sharks
More than 450 million years ago, sharks with a cerebellum emerged. This organ coordinates complex, time-critical behavior. When hunting, the shark might have had to outmaneuver its prey and then bite at the right moment. Similarly, its prey had to come up with movement strategies to navigate through the water to evade predators, locking predator and prey into an evolutionary race. Mammals face similar challenges when trying to jump from tree to tree, evade attacks by predators, or trying to catch prey.
Cerebellum The cerebellum is the brain part that helps with coordination of complex behavior. It provides a set of motor programs the brain can pick from repeatedly for similar actions (even in time-critical situations). With the help of the cerebellum we can, for example, walk or bicycle without having to consciously think of each movement.
In more general terms, the cerebellum is used for anything that needs to be replayed. In that regard, while we are living a more sedentary lifestyle than our ancestors, we still use the cerebellum in our daily lives. For example, think about how each leg moves, as you did when you first learned to ride a bicycle or walk: the programs to coordinate all your motor neurons were not yet transferred to your cerebellum (“learned”). Thus, they were not yet optimized and consequently, they were very slow. Until that optimization happened, walking or riding a bike had not become “second nature.” You had to take “baby steps” and focus on one step or motion at a time before making the next one. Given that both the cerebellum and the basal ganglia are involved in coordinating motor programs, it is no surprise that they also form an integrated network to exchange information [Bostan and Strick, 2018].
In the (very rare) case of people born without a cerebellum, we see late walking development, reduced gait speed, unsteady gait, and a reduced ability to stand in darkness or when their eyes are closed [Yu et al., 2014]. This is explained by the fact that the cerebellum is connected to the inner ear, providing our sense of balance. In addition, people born with without a cerebellum have late speech development, slurred and slowed speech, and a reduced control of pitch and loudness. This points to an additional role of the cerebellum in language fluency, social behavior, and the reward system [Carta et al., 2019].
5.1.10 The Neocortex in Mammals
The neocortex, layered over the collicular control of attention (above the previously mentioned superior colliculus), developed more than 300 million years ago. Following the Permian-Triassic mass extinction event 252 million years ago (extinguishing 70% of land biodiversity), both the dinosaurs and mammals emerged. Given that dinosaurs still dominated the planet, mammals had to move into a niche and become nocturnal animals. According to the nocturnal bottleneck hypothesis, traits of growing fur, managing body temperature, and well-developed senses of smell, hearing, and touch helped our ancestors to stay active at night while evading predators during the day.
Nocturnal bottleneck hypothesis The nocturnal bottleneck hypothesis posits that many mammalian traits like growing fur, managing body temperature, and well-developed senses of smell, hearing, and touch were adaptions to moving into a niche to become nocturnal animals. This adaption was necessary to evade the dominant dinosaurs who roamed the Earth during daytime.
Functions of the neocortex include sensory perception, conceptualization, directed motor commands, spatial reasoning, communication, and long-term planning. The visual field is analyzed to create a mental representation of objects and their location. Instead of the raw sense data, this mental representation of the world is then used by the rest of the brain in, for example, coordination with motor control, language (reading this book), or face recognition. Similarly, other senses (hearing, touch, smell, etc.) are processed, and their signals are categorized and prioritized.
The core task of the brain is to decide what to focus on and nervous systems are about linking specific sense data to specific actions. This is why classifying signals to focus on the important parts (like changes) of sense data was one of the first evolutionary steps towards our brain. It allowed processing more sense data, and enabled the evolution of additional sense organs like the olfactory system and the visual system. With those new senses in place, the next evolutionary step was the optic tectum to track visual signals to keep the attention on, for example, moving prey. Adding context information by combining sense data in the thalamus allowed for more refined actions, but also required additional arbitration using the basal ganglia. To solve conflicts between competing signals, the amygdala allowed an animal to learn to prioritize signals instead of just following the strongest one. Combining these different learned experiences with the help of the hippocampus then enabled planning and navigation. Fierce competition between predator and prey led to an optimization of the basal ganglia to memorize selected motor programs for quick retrieval later.
While we are now aware of the principal brain functions we share with other mammals, the question remains what makes us humans unique. In the next section, we will look at how our human ancestors adapted to the Savannah and how that set them apart from their closest primate cousins, the chimpanzees, that stayed behind in the forest.
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