This is the second post in a series inspired by Todd Feinberg and Jon Mallatt’s new book, ‘The Ancient Origins of Consciousness: How the Brain Created Experience‘.
The first post in the series was: What counts as consciousness?
Life appears to have gotten started fairly early in Earth’s history. The oldest known fossils are now dated to be about 3.7 billion years old. Given that the Earth itself is only around 4.5 billion years old, and that considerable evolution would have had to happen for the earliest fossils to exist when they did, life probably got started as soon as conditions were conducive for it. (Note: “as soon as” on geological time scales.)
For billions of years life evolved and gradually became more complicated. Around 1.5 billion years ago, the first multicellular life emerged. Just as cells had communication mechanisms, motile (animal) multicellular life began to develop its own communication mechanism: nervous systems. The first nervous systems were basically nerve nets, more or less evenly spread throughout the animal. They enabled the organism to respond to things like pressure somewhere on its outer layers, or to noxious or attractive chemicals. Nerve nets basically just had reflex action, direct responses to environmental stimuli.
By the end of the Ediacaran geological period, around 550 million years ago, bilateral animals (with two duplicate halves) had appeared, with a nerve cord running down their center. Animals of this period either didn’t have self locomotion or had only a very primitive form of it. They generally all fed on a thick green mat of microbes that existed on the ocean floor.
Animals with the central nerve cord (chordates) did have centralized reflexes. Some had light sensors on their head and other limited senses. None of these senses had enough resolution to do more than give small hints on what was happening in the environment. Which was fine, because the organisms at this point didn’t have enough processing power in their nervous system to use more information anyway.
But in a few tens of millions of years, during the Cambrian period, not long on geological scales, the animal kingdom would suddenly explode into a much wider range of body types. The onslaught of development would be so sudden and rapid, that geologists and paleontologists call the period the Cambrian explosion. Most significantly for this post, primary sensory consciousness would develop.
Why did evolution suddenly speed up during this time? There are various theories, but most evolutionary biologists seem to think the most plausible reason is an arms race. The term “arms race” is a military one, referring to two competing military powers increasing their armaments because of what the other competing power has, resulting in both having an escalating inventory of weapons far in access to what either needs aside from countering each other. One historically recent example was the Cold War era missile arms race between the USA and Soviet Union.
In the context of evolution, “arms race” basically refers to selection pressures that come from competition rather than from the rest of the environment. What was the arms race in the Cambrian? Predation, animals eating other animals, suddenly became prevalent. This might have happened because of overpopulation and depletion of the microbe mat mentioned above, or maybe due to some other unknown change.
Whatever caused it, it put much more selection pressure on prey species, and eventually on other predators as prey became more elusive and scarce. Evolution seems to have responded in a variety of ways. Some species developed hard shells, making themselves more difficult to consume. Others burrowed deeper into the sea floor. Some developed hard shells but stayed mobile, holding an advantage because of them. These were the arthropods, and they appear to have been the main predators of the period.
But one group went the way of speed and agility, the ability to flee or evade. This involved developing an inner skeleton, unlike the outer exoskeleton of the arthropods. They developed a central support structure, a backbone, and became the first vertebrates. But their movement strategy required distance senses, such as eyesight, smell, and hearing, to collect information on the environment, and robust central coordination to make use of that information for movement, movement to evade predators, to fight or try to escape.
Of course, arthropods, as the predators, soon needed to respond in kind, although their brains didn’t rise to the level of sophistication that the vertebrates did. Part of this might have been because their exoskeletons required periodic moulting, constraining their growth. Nevertheless, both groups went on to develop complex brains and, arguably, consciousness.
Both developed high resolution eyes (relative to the light sensors that had existed in the Ediacaran), that allowed them to build image maps of the environment. As I mentioned in the last post, these weren’t human level maps, but they were still effective models that allowed the animals to make predictions. They had built inner worlds which now guided their behavior. Although their inner experience was at a far lower resolution than ours, it increased their chances of survival.
There would be other major milestones in cognitive development. Jawed vertebrates would soon have larger brains. The first land animals would have larger ones yet. The mammalian cerebrum would eventually come along and dramatically increase the information in the internal models. They would continue to grow in size and sophistication, eventually leading to the rise of social species in the last 100 million years.
The biggest developments, from our point of view, would be the rise of primates, and eventually homo sapiens. Interestingly, it seems that human intelligence was the result of another arms race, this time among humans. Human intelligence was likely heavily selected over the last million years for social intelligence, rather than any other environmental factors, with a higher level of social intelligence, a better theory of mind for one’s peers and oneself, resulting in increased reproductive success. Eventually it would result in modern humans, with human levels of consciousness.
But sensory consciousness started in the Cambrian with the rise of image maps, internal neural patterns isomorphic to patterns in the environment (to varying levels of success), or what I prefer to call models, inner worlds that dramatically increased the causal information, the scope of the environment that the organism could respond to. And we owe that start to the rise of predators.
The next post will get into types of sensory or primary experience.