It's reassuring to think humans are evolution's ultimate destination—but research shows we may be an accident

Though evidence suggests we could be an accident, it is comforting to believe that humans are evolution's ultimate aim.

As though evolution had a purpose, it is comforting to think that sophisticated bodies and minds such as ours are an unavoidable byproduct of evolution. Sadly for human egos, a new research comparing more than a thousand mammals—our own group—showed less than idealistic results.

Jean-Baptiste Lamarck and other evolutionary scientists of the late 1700s reasoned that life must have an inbuilt urge to grow into ever more sophisticated forms, and they felt that this showed God's plan. Natural selection, as Charles Darwin demonstrated by the middle of the 19th century, has no set course and can occasionally lead to the simplification of species.

Although most modern biologists believe that during the past 4 billion years, the most complex species have gotten increasingly complex, they dispute as to what kind of process is responsible for this.

Being largely still extremely simple, one possibility is that maximum complexity has "accidentally" grown, as ink diffuses in water. In the event that this is accurate, it may be a setback to our belief that humans are the most sophisticated species.

There is also the hypothesis that natural selection drives increased complexity on average. Occasionally, selection operates in a comparable and parallel manner on several, independent branches of the tree of life. This is referred to as a driven trend and can have comparable impacts in several of those fields.

Driven patterns may not necessarily indicate a divine design, but they do reassure us humans that complexity was largely an improvement.

So which pattern—unintentional diffusion or driven trend—is more prevalent in the evolution of complexity?

Most alterations and mutations are detrimental, and stabilizing selection, which works to preserve the status quo, often weeds out harmful variations. However, since the majority of mutations lead to reduced functionality, shouldn't this make it very challenging for unique evolutionary traits to emerge?

In actuality, evolution frequently works with many copies of one organism. For instance, two copies of a same gene might exist in the same organism.

As long as one copy continues to work as intended, the other duplicate is free to undergo mutations without immediately harming its bearer. Usually, these altered copies are eliminated over time, but sometimes they develop a new feature that is advantageous.

What's even more amazing is that whole genomes, or all of an organism's genes, may be replicated in a single generation. It is quite likely that copies of some genes will take on a new role under these conditions.

Sturgeons and paddle fishes, for instance, may have survived the greatest mass extinction in history, which wiped off 96% of other marine species, because they experienced a complete genome duplication 250 million years ago.

Additionally, duplication methods may be used to create identical replicas of things like limbs and segments. For instance, although millipedes have more legs, their design is essentially the same.

In contrast, shrimp have a wide variety of modified legs that are used for walking, swimming, and egg-laying. According to a biological concept known as the zero force evolutionary rule, unless stabilizing selection occurs to maintain the status quo, these duplicates will tend to become less similar through accidental diffusion alone. Naturally, if there is a benefit to this, natural selection may also work to lessen the similarity between the clones.

Our study demonstrates that there are both diffusive and driving components to animal complexity. Mammals developed in many diverse ways, with just a few lineages pushing the boundaries of complexity, rather than marching towards ever-greater complexity.

Surely complexity is something selected for in nature?

Regretfully, not much study has been done to answer this query. One of the few published studies shows that throughout the previous half-billion years, crustaceans—crabs, lobsters, shrimp, and their relatives—have developed with a determined trend toward increased complexity.

Similar to all other vertebrates, including crustaceans, our bodies are composed of repeated tissue blocks called somites. These are most noticeable in our ribs, vertebral column (also known as our spine), and a lean athlete's six-pack. Mammals differ in the quantity of vertebrae, or the spine's bones, and in how they are fashioned for certain functions in the neck, thorax, back, sacrum, and tail.

One measure of complexity common to all mammals is the number of bones in various locations. Many taxa, including whales, bats, rodents, carnivores, and our own group, primates, independently acquired sophisticated vertebral columns in our study, which sampled over a thousand mammal species. This implies that more complexity may be a winning combination and that several branches of the mammal tree are experiencing this due to selection.

Many other branches, on the other hand, either reach a low complexity plateau or even get simpler. Despite having relatively basic vertebral columns, animals including elephants, rhinos, sloths, manatees, armadillos, golden moles, and platypuses have all managed to live. Context determines the course of evolution in every way.

We still don't know a lot about the evolution of complexity because the field's research has just lately begun to pick up steam. All the same, we do know that the process of mammalian evolution has not been a directed "march of progress," but rather resembles a random diffusion walk in many ways.

Provided by The Conversation