Why do advanced lifeforms exist?

Question

If bacteria and other simple prokaryotes are so abundant and successful, why did larger, more advanced organisms like animals and plants evolve at all? What sort of advantage do these sorts of lifeforms possess that would favor them?

Answer 1

As already stated, the answer is evolution. At the molecular level, variations on themes present in bacteria occurred, and sometimes those variations led to organisms that reproduced faster/better than others. Sometimes they didn't. But like crabgrass in your yard, once a form came along that "bred" better, it took over in that specific environment.

These new life forms were also subject to variation, and anything new that came along that was better suited to reproduce in a given environment probably did just that. Remember, each of these variations was due to mutations in the DNA of the organism, meaning that asexually reproducing organisms would likely pass the mutation on to all progeny, and eventually when sexual reproduction came along there was still a chance of heritability of these genetic traits. Importantly, this process took/takes many many generations to happen, and many mutations were probably lethal or came with trade-offs (e.g., these are mutations that lead to tiny changes in specific proteins - many proteins have more than one function in a cell, so if one gets mutated and works better for one process, its role in a separate process may also be affected, for better or worse). And, the more chemically/physiologically complex the organism, usually the larger its genome, adding to the range of possible mutations. So this all took millions of years.

We'll probably never know exactly what the conditions were on earth that specifically led to the landmark transitions, but we can infer some of them through the adaptations seen from bacteria to eukaryotes, and most dramatically from unicellular to multicellular organisms. It's possible (haven't kept up on the debate in years) that some attributes of eukaryotes, such as mitochondria were actually events of one life form being incorporated into another, hence the separate genomes of mitochondria and cell nuclei. Further, one has to consider the "negative" in evolution, such as the elimination of genes or traits that no longer conferred advantages in a given environment - we tend to think of evolution as gaining advantages or leading somewhere. It's not that at all. So there's likely a LOT of things that happened in the last 4 billion+ years that we'll never be certain of. Like with human wars, it's the winners who tell the history.

As to more of the philosophy of why bigger seemed to equal better, etc., an analogy might be drawn to human businesses/corporations. Small businesses can do fine, even quite well, in their own specific niche market, as long as competition is low and supply/demand work out. But some small businesses do better than others and sometimes those businesses grow. They start opening more stores, for example, grow their supply chain and distribution, and essentially get bigger than the rest. Some then go out and invade other niches and outcompete those little businesses that did so well with a static environment. As it seems right now, the biggest businesses with the biggest markets and control over their resources seem to be the best, seen by the omnipresence of Walmart and other big-box-type stores and chains. But small businesses remain in the background, still working, still going unnoticed by the giant corporate organisms. And sometimes the environment changes. Recessions happen, resources change, costs go up (or sometimes down), technology changes, and suddenly there's opportunity for new/different businesses to get in the game, do well, and either stay like that or grow. And the cycle continues.

Sorry, longwinded and tangential. But the idea is that evolution happens based on environment and potential for adaptation by the organism through genetics. Those that do well, continue. And doing well in an environment of abundance often means adapting to use more of that environment. If bigger means getting to use more of the environment, then bigger wins. But watch out for those changes. The big guys don't like changes. The bacteria do.

Answer 2

You ask what sort of advantage do advanced lifeforms (assuming you mean multicellular) possess that would favor them over bacteria (which are prokaryotes) and single-celled protists, the answer is quite simple.  

Multicellularity itself is an advantage over single-celled life, whether it is bacteria or protist.  Multicellularity allows for specialization of individual cells, enabling them to focus on related or single tasks.  This allows them to become highly specialized and more efficient at what they do.

With specialization comes the need for cooperation among cells of differing specializations.  This began as colonial groups of single cells.  Working as a coordinated group, each with specializations (many of which may have been separate functions within a single cell but are now the main function of the entire cell), the multicellular organism is more successful at securing resources such as food, water, and living space.  This leads to greater success with reproduction and passes the traits on to offspring.

This does not mean the success of bacteria and other single-celled organisms is totally replaced by multicellular, advanced lifeforms.  The single-celled organisms still holds a vital role in the overall survival of life in general.  

Consider it as a giant company.  Every life has a specific job to do.  As the company grew, new jobs developed that were better accomplished by more specialized and advanced lifeforms.  The earlier positions were not destroyed, but may have changed slightly.  Every aspect of life has a function or job function that it serves.  

Many new jobs are created by the simple act of becoming "advanced" as you put it.  By becoming multicellular, new jobs opened in the company that enabled more specialization and the development of more advanced multicellular life.  As life diversified as multicellular organisms it opened the opportunity for more diversity.

Hope that helps, sorry for the length.

Answer 3

One word: evolution.

Evolution has no purpose and is not directional. Eukaryotes just happened to exist and survived. The first eukaryotes probably fed on bacteria, and found plenty to eat. So clearly a more advanced form has an advantage.

Answer 4

Random chance gave rise to the eukaryotes. From there it was sexual selection and natural selection that emphasized certain attributes and qualities in certain environments that gave rise to more advanced life. It was also an abundance of resources to use for nutrition that allowed larger, better bodies to develop... and in humans for larger brains to develop over time.