"Who wants to live forever?" - Queen
Tl/Dr: if you want biological immortality, you have to earn it. You have to be able to cope with unexpected disruptions on all scales up to that of specialization, then you can go about trying for immortality.
Forever is a very long time. Even if we reduce the lofty goals from immortality to merely biological immortality, we still have to challenge the way we think about the world to make sense of it.
Nature has no concepts of the individual and the species. Nature does not evolve species to make them more fit -- nature works on a continuum. Individuals and species are human constructs designed to make sense of the reality we face every day. In many cases these human constructs do a remarkably good job of describing the world around us. We can quickly separate many interesting regions into individuals, then categorize those individuals by species. It works pretty well... most of the time.
There are cases where the line becomes more blurry. Bacteria are an excellent source of examples of this. They can form so-called "bio-films" if they sense that there are enough bio-film ready bacteria present in an area. In bio-films, we see behavior more associated with a single multi-celled organism than we do in a cluster of individual single-celled organisms. For example, we often see "dispersion," a key step in the bio-film where it "chooses" to go colonize other surfaces, similar to a tree seeding. The line between individual and group is quickly blurred in these uncharted dark waters of speciation.
Another interesting challenge for our definition of an individual is Pando. Pando is a clonal colony of a single male quaking aspen. You or I might look at it and see it as a collection of individual trees, but if we were to take genetic samples from the trees, we would find they are identical. Pando's roots intertangle and interact with eachother, like many root systems do. If you introduce a beetle to one side of Pando's massive 106 acre body, the tree you introduce it to will react to the beetle. It will send messages through this root system causing trees on the other side of Pando to start releasing chemicals to deal with that beetle!
Even the concept of a "species" is not sacrosanct when you really start looking at it. We see plenty of examples where it gets murky. One example is cross-species breeding, such as breeding a horse and a donkey to create a mule. In this case we create an "individual" mule, but it isn't considered part of either species (and it happens to be sterile, so it can't be its own species).
Periodical Cicadas are an intriguing bit to classify into species. Periodical Cicadas emerge for breeding on either 13 or 17 year cycles. This is a very effective evolutionary approach: predators can't gorge themselves fast enough on the emerging Cicadas, so the vast majority get to breed. There are 7 species of them in North America, typically grouped into 13-year and 17-year groups. However, it is also popular to break them up differently, into 3 groups based on morphology: the Decim species group, Cassini species group, and Decula species group. As it turns out, there are marked similarities between some of the 13 year and 17 year cicadas. The only reason they are considered to be different species is because they emerge on different cycles (that only line up once every 221 years!).
Also consider the interesting world of Lateral Gene Transfer. This is a method bacteria use to transfer DNA from bacterium to bacterium, as opposed to relying solely on the more traditional vertical gene transfer from parent to child. This is a very common vector for trading information about resistances to antibiotics. Not only does this work within a species, but it actually works across species of bacteria! In fact, it even works between kingdoms: There is human DNA in the bacteria responsible for gonorrhea, believed to be transferred by lateral gene transfer.
So if we can't rely on the traditional lines between individuals and species, what can we rely on? One approach I have used is to study "long lasting" self-replicating patterns. This has a few nice behaviors:
- The definition of "long lasting" is fuzzy, so we can discuss nature on a continuum rather than pinning it down to discrete steps (such as "a segment of DNA which remains intact for 10,000 years").
- We can permit some level of inaccuracy in our definition of "self-replicating," which is good because DNA replication isn't perfect.
- If we look at the long-lasting patterns, we do often see gaps which make it easy to capture the concepts of the individual and the species where those distinctions are clear. In the regions where they are not clear, we aren't obliged to trap ourselves into this way of thinking.
We can use this approach to capture a concept of who you are. We typically start "you" at conception, when your cells become genetically dissimilar enough from your parents and they undergo an electrically-stimulated transformation that, if you weren't "you" at that point, could only be considered a malignant tumor on your mother. After birth, we track a rather long-lived pattern which slowly shifts over time as you grow up, but all humans agree that this "perdurable" entity is "you." At some point "you" die, but parts of what made you up live on. If you had children, they share some of your DNA -- that pattern lives on longer than you. If you have a legacy, that pattern lives on. If you were an organ donor, your organs may last longer than you do.
So now we can talk about patterns that "should" live on. I put "should" in scare quotes, because if we're talking about evolution, we have to be careful with assigning purpose. However, we can see some things which seem darn similar to "purpose." For example, the majority of your DNA, the part shared by all humans, has a very strong interest in preserving your DNA. Over time, mutations creep up in DNA, and some of those may be so detrimental to preserving your DNA that there's huge bodies of genetic code dedicated to making sure you die before that happens. This is one reason why it is considered risky to have children when you are older; you have collected more mistakes in the DNA. Some of these mistakes might destabilize the longer-lasting patterns of humanity.
Some of these "mistakes" are a bit more subtle. Consider the evolution of society. The human genome is tailored to encourage societies to form. Each society itself is a long-lasting pattern. The United States of America is nearly 250 years old, and many nations have existed far longer than that. These patterns also have to ensure they are not disrupted. The key to this is that random stuff happens. There was no way to predict that a Ghengas Kahn or a Napoleon or a Hitler would happen to be born in a tumultuous time. So the society has to be able to cope with this, as it happens. If the society falls apart, the human genetics is at risk, so we have a genetic drive to preserve our societies.
There's two extreme solutions to this problem. One is to identify when things go wrong, and fix it; the other is to prepare so that things cannot go wrong. Each of these extremes has issues. If you fix the issue after it happens, you're trusting that you'll be given a chance to fix it. A candle, once snuffed out, never gets a chance to warm back up its wick. If you rely on fixing things after they happen, you are reliant on there being a "quiescent" period after the event where you have time to figure out what happened and fix it. Needless to say, this never happens in war, but it is a very effective approach for natural disasters like earthquakes.
The other extreme solution is to prepare ahead of time. This involve hardening yourself (at any level: individual, society, species, or otherwise) so that you are less affected by change. We build defensive structures so that we are ready for war. However, this approach is energy inefficient. You spend a lot of time preparing for things that never happen. You also create weaknesses. If an opponent can hover just outside of the range you protected for, you find yourself defenseless and you never practiced any other approaches for ensuring the long-lastingness of your patterns.
The interesting region is the middleground between the two, when it isn't so clear whether you are preparing or responding. When a long-lasting pattern responds to something as it happens rather than before or after it happens, they can be far more efficient than either extreme would be. This is where the majority of bodily functions operate. My personal favorite, the Patellar Reflex, is designed to catch us when we land. It's the reflex that occurs when your doctor taps your knee to watch it jump. When you land, you have a very short window of time to respond. If you prepare, by tensing your muscles, you transfer the shock from the legs (which are built to withstand the shock) to the spinal column (which is not). If you wait for it to happen, and the fix it, you crumble to the ground. However, the instant the body sense a stress on the patellar tendon, in front of the knee, it uses a monosynaptic arc, the fastest neurological connection in the human body, to tense your legs at just the right moment. By responding in the moment, we remain a long-lasting pattern.
So we finally have the crux of our answer: to cultivate biological immortality, one must be prepared to protect your DNA from any surprises the universe may bring your way. You have to have powerful DNA repair technologies to defend against UV radiation, and even more powerful DNA analysis tools which will let you analyze any irreparable breaks to see if the changes are beneficial or detremental. You have to have a biological structure which protects you from the environment. If there's cliffs that are 30 feet tall, you either need a body that can withstand a 30 foot drop or a mind that can ensure that you'll never find yourself jumping off a 30 foot drop unexpectedly. If you use a society to keep you safe, you need to make sure that society is prepared to deal with the robbers and the rapists and the genocidal maniacs. Only then will our genome admit that it is safe for us to become biologically immortal.
You can push for biological immortality without trying for this balanced approach, but it doesn't end well. Nietzsche wrote on the topic in Thus Spoke Zarathustra. In that story, "the last man" was a group who pushed for immortality above all else. I'll leave it to you to read, but needless to say, Nietzsche has some pretty strong words to have with that topic.
So what can we do? Well, we can look for existing long-lasting patterns which encourage us to have this sort of in-the-moment resiliency ourselves. There are plenty of approaches out there, and each has its own little piece of the puzzle. Due to my path through life, I find the ones which capture my eye are the martial arts. They teach you how to respond in the moment whenever you can, and only resort to violence when you have run out of options.
The result? I think it shows. Consider Baugua grandmaster Lu Zijian, who passed away 4 years ago at the ripe old age of 118! He taught up until the bitter end, and I think it's pretty clear that he's responded to the surprises in his life pretty darn well!
"Who waits forever anyway?" - Queen