They call it “The Hard Problem” of consciousness; it is commonly described as, “What is it like to be a bat?” Effectively, how can you break down consciousness into a definable set of components so that you can both understand consciousness and identify life forms that have it. They test the problem with various thought experiments, such as if there was such a thing as a zombie who had full motor functioning, etc., what the difference would be from a conscious human and what capabilities it would need to demonstrate to be conscious.
We’ll stick with layman’s explanations for this post—no need to get technical here—but my personal opinion is that the reason why it’s a hard problem is that it is a combination of factors that create human consciousness that exist in various degrees in different organisms. For example, you can break how you know humans have consciousness by things like language, senses, brain activity (at various levels like sensory processing and thought), the ability to reason, and even through its altered states of consciousness like sleep. These identifying markers are a subset of what makes humans the most advanced creature on planet Earth, a larger set of capabilities that include opposable thumbs, bipedal movement, the ability to create tools, etc. This has to exist on a scale/spectrum because primates have opposable thumbs, bipedal capability, the ability to communicate, etc. and are also conscious, but they don’t have the advanced capabilities of humans. They are definitely conscious, though, by all commonly accepted definitions (note: consciousness is different from “sentience” and “intelligent”, though those also exist to varying degrees and aren’t definite).
Additionally, there are different ways to experience consciousness, as the “bat” part of the “What is it like to be a bat?” version of the question points out. Bats, of course, use high-pitched noises and their advanced sound detection capabilities to perform the equivalent of what humans do with sight: detect objects in the environment for the purposes of finding food and avoiding threats. Because of this, of course, bats experience reality in a fundamentally different way. Their brains are wired differently, they as organisms function differently, they likely don’t get a “head rush” like humans do from hanging upside down, and they can experience the true sensation of flying by flapping their wings. That’s a fundamentally different life experience than other organisms, even though they likely experience similar feelings of touch, taste, etc. like humans because of what capabilities we do have in common.
So the fundamental question is, can you draw a line between organisms that are conscious versus those that are not, and could you define what the precise difference is? Honestly, I’m both a pragmatist and a nit picker on this one: on one hand, it doesn’t matter because we know that humans and other animals are conscious because of attributes such as large brains, the need to sleep, social interaction, fight-or-flight responses, and a variety of other definable characteristics make it pretty clear; on the other hand, technically you could define consciousness as simple awareness of the world around it and expand consciousness all the way to microscopic organisms that have the basic ability to respond to stimuli, make choices (amoebae, for example, choose a more optimal food source when given two options), and seek the means of growth and reproduction. Maybe this is being dismissive of the original question, but I think it is good to test definitions and look at how the line you draw affects the conclusions you can draw from it.
There are a few implications for life and meaning in this question. The first is, of course, the ethical one that most people consider when deciding what food to eat and whether to make controversial acts like abortion legal. If animals are conscious and can feel pain, then many people think they should not kill them for food. The natural retort is that plants have stress response systems that activate when being cut, so if you use a looser definition of feeling pain, then that would qualify. Similarly, many people use consciousness as an important milestone to determine when a fetus can feel pain as to when it should become illegal to end a pregnancy. The retort here is that consciousness is not an appropriate line for human life because all human life has value and deserves protection. As usual, the choice is yours how you wish to proceed. (I don’t suggest specific ethics because it goes against my rule of not combining how life works with how to live your life)
The second implication is what role consciousness plays in meaning, purpose, and significance in life. There is a common perception that organisms with higher consciousness are “worth” more, but that is only required to define in one case: laws. For example, if you run over a neighborhood squirrel, that has to have a different legality than if you run over a neighbor’s dog or your neighbor. You would likely have no problem “bug bombing” your home if you had a bug infestation, but you would likely prefer a lizard, stray cat, or even a family of raccoons to be caught instead of killed. The reality is that we all do complex calculations, such as how many of those types of organisms are on the planet, whether they are capable of being safely completely removed, and even how “cute” they are to you.
The scary-for-modern-times reality is that not even all humans had the same value under the law until recently in human history when there was generally enough resources to go around and property rights became more respected. So people even did calculations whether other humans were “worth” helping, protecting, saving, etc. We still have to do that today in areas like how healthcare systems decide whether to give someone one treatment or another given the costs to the system—and we still treat some people as more important based on fame, etc.—but many civilizations have reached equal value and rights as a human under the law. The truth is, however, that consciousness as a line for ethics and value is more of a relative line based on abundance and not an objective one, as history has demonstrated with its shifting ethical line throughout history.
The more interesting implication is around meaning and purpose. The most direct implication is that, as a conscious organism, you have control over your decisions and actions—albeit you are strongly influenced by your genetics. Humans are fortunate enough to have impulse control and rational thought thanks to their prefrontal cortex, which is what people often think of as “conscious” when they mean rational and mindful, such as to be “conscious of someone else’s time” when you are considerate and pay attention to how you are using it. The great news is that you get to use that highly evolved thought process to determine your own destiny, as you choose where to live, what to do, what skills you develop, what you think about, and what you pay attention to. Whether you use your opposable thumbs, language, prefrontal cortex, dream content, or any other aspect that demonstrates our capabilities as humans with advanced cognitive functions like consciousness is almost irrelevant; the point is that you are conscious and that gives you the ability to live your life the way you decide with said capabilities.
So if you ever wonder where the line is that denotes consciousness, remember that there is a scientific answer, which they’re still working on (as of this post), and the more pragmatic and philosophical answers, which are analyzed for their application to how you can decide to live your life. Appreciate all of the capabilities you do have that give you the ability to ask that question, and then make the choices you feel are right for you as to what the implications are regarding which ethics you should hold and what significance you give to different parts of the world around you. Consciousness is a complex combination of brain functions—and, in my opinion, likely a “meta-capability” or an intangible capability that exists in a unique state based on the nature of its component capabilities—and so it might still be a while before scientists and philosophers agree on what it is like to be a human vs. a bat and how their different genetic capabilities affect their life experiences.