Matters of life and death

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Matters of life and death
Matters of life and death
Anonim

There are only five major mysteries in modern biology.

Microorganisms

Riddle one: where did life come from?

Biology - translated from the Greek "science of life" - has no idea where the subject of its study came from. The situation is not unique - physicists, for example, also do not understand very well how exactly Planck's constant or gravitational force arose. But only in biology, perhaps, questions about the "beginning of the beginnings" are of such acute importance.

The American geneticist of Soviet origin Theodosius Dobrzhansky said that nothing in this science makes sense if it is not passed through the theory of evolution.

Biological science is based on the classical, descriptive disciplines: zoology, botany, microbiology, etc. And somehow it goes without saying that the purpose of the research of each of them is as detailed as possible clarification of one or another branch of the evolutionary tree.

At the same time, over the past hundred years, a huge part of biology has branched off from the original, descriptive science and merged with medicine, forming a single biomedical branch. It is characterized by a different approach, analytical. The scientist does not just describe the mouse - he grafts new genes into it and observes the result. But why are we so interested in mice, monkeys and fruit flies? The answer is simple: thanks to the theory of evolution, we know that the work of the mouse organism is fundamentally no different from the work of our own. As a result, analytical biology has far more practical benefits than descriptive biology.

But there is a third form of biology, which is just beginning to emerge these days. Today's "analytical" biologist modifies a living organism to understand how it works. Tomorrow he will create organisms from scratch for this - this is the approach of synthetic biology.

Indeed, the surest way to understand the structure of any mechanism is to build it yourself. Already today, scientists are able to synthesize whole genomes in a test tube and make them work in a living cell. This experiment unambiguously shows which genes are necessary for the existence of life - which means that it opens up unprecedented opportunities for their modification, modification and submission to our will. The discoveries of analytical biology are made “from top to bottom”: the organism decomposes into as basic components as possible. Synthetic biology, on the other hand, explores living things "from the bottom up": the whole organism is composed of as many basic components as possible.

But how to start “synthesizing life” if there is so little that is understood in the origin of life? In the aforementioned example with an artificial genome, scientists inserted it into a living cell, from which its own DNA was removed. Thus, of the two main components of living things - the cell and the genes it contains - scientists have so far managed to synthesize only one.

Life appeared on Earth about 3.5 - 4 billion years ago: by geological standards, almost immediately after the formation of the planet 4.5 billion years ago. But any serious "chronicle" of today's biology begins much later: by that time, cells were already breathing oxygen, diligently synthesizing thousands of proteins, many of them have long been united into multicellular organisms that already knew how to mate, actively seek food and even memorize information.

For a synthetic biologist, the most ancient stages of evolution, lost in centuries, are fundamental, during which the basic principles of organizing living things were laid. Why, for example, are proteins composed exclusively of levorotatory amino acids? The chemical structure of these "beads" of protein chains is such that they can exist in two mirrored forms, called left and dextrorotatory.It would seem that the chemical properties of these molecules do not differ: they consist of the same atoms at the same distances from each other. Nevertheless, all living things use exclusively levorotatory amino acids.

Is there a deep meaning in this, or is it an accident we inherited from the "original" cell? Is it possible to create a "dextrorotatory protein"? "Dextrorotatory organism"? Will they be different from other living things? These mysteries are directly related to the origin of life. The list goes on: is phosphorus required in DNA? Is life possible without a cell? What chemicals are needed for self-replication? The practical possibilities behind these questions are endless.

Even if life was brought to Earth from space, as many believe, this does not in any way change the questions facing the evolutionary - and synthetic - biology of the future. If life did not appear on Earth, then where, and most importantly - how? It is likely that this mystery will remain unsolved - although no one knows what discoveries tomorrow will bring.

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Riddle two: where did we come from?

In whatever form life first appeared on Earth, after three and a half billion years, evolution gave birth to the direct ancestors of the species Homo sapiens - Homo sapiens.

The origin of this unique monkey is much better understood than the evolution of most other species. But for obvious reasons, our attention to the issue is much higher than when applied to other animals. We are not very interested in how the ancestors of voles or partridges migrated across continents. But when it comes to our closest relatives, their travels around the world and interactions with each other turn into a real historical detective story.

More recently, scientists have built the entire genealogy of the human race on bones. Skeletons found in different parts of the world were analyzed for such features as the structure of the teeth and the volume of the skull. Based on these data, the skeletons were grouped into species, and based on their similarities and differences, a picture of the gradual transformation of stupid monkeys into smart people with a stick in their hands was built.

As it has become clear in recent years, this picture has little to do with reality. The evolution of the closest human ancestors is not a sequential transformation of some species into others, but a branched tree with many dead-end branches. It can be extremely difficult to understand exactly how these branches are related to each other. Today, the latest technologies for analyzing DNA obtained from fossil remains help us in this.

For example, we are witnessing an action-packed scientific drama about the relationship of our direct ancestors - early Homo sapiens - with their cousins: Neanderthals and Denisovans.

Did labor create man?

Until the 20th century, archeology was a rather shaky science, inclined to see evidence of human greatness in every bone found. Among the slender, but completely unfounded hypotheses of early archeology, the idea stands out that the mastery of tools - an allegedly unprecedented phenomenon in nature - directly determined the appearance of people. Echoes of this hypothesis are heard in the name of the species Homo habilis - a skilled person who was previously considered the most ancient representative of the genus Homo.

Today it is clear that the use of tools is far from unique to humans. With stones and sticks, for example, the ancient monkeys - pananthropes, were good at handling. Modern animals, such as crows, dolphins, elephants and, of course, many primates also use tools. Scientists still argue about what exactly made human ancestors stand on their feet and develop a huge brain, but the excessive romanticization of "skill" is outdated today.

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In 2010, the Neanderthal genome was decoded. Based on the analysis of the data obtained, it was concluded that this species, previously considered independent, actually actively interbred with our ancestors and brought from 1 to 4% of genetic information into the DNA of a modern European.

Not long before that - in 2008 - another "cousin" of a modern man, a Denisovite, was discovered. He, too, was not averse to hitting on "reasonable" young ladies: today's residents of some regions of Southeast Asia have 3-5% of his DNA left.

For some time, a rather slender picture of this love triangle lined up.In Africa, three branches of the genus Homo arise from a common ancestor. Neanderthals migrate to Europe, Denisovans to Asia. A third branch remains in Africa. She gradually turns into a Homo sapiens and goes for a walk around the world, "picking up" the corresponding genes in the west and east from the "cousins" already living there. In the future, Homo sapiens displaces both those and other cousins ​​from the face of the Earth (exactly how - another white spot in history), but retains the "prints" of both Neanderthals and Denisovans.

However, more recently, scientists from the Institute for Evolutionary Anthropology in Leipzig have managed to decipher part of the genome of the common ancestor of all three branches of human evolution. Despite the fact that this ancestor was not yet Neanderthal or Denisovan, his remains were found in Spain - based on the accepted picture, it turned out that he had to leave Africa and set foot on the path of "neandertalization".

However, the results of the genetic analysis were shocking. The DNA of the "Spanish" man turned out to be much closer to the genome of the Denisovan, which should not have been in Europe at all! It turns out that the whole picture of our relations with the Denisovans and Neanderthals is far from an indisputable fact.

The described example is just one of the many open questions of modern paleoanthropology. Only religious fanatics today doubt that man descended from a monkey. But what exactly happened to our ancestors for a couple of million years, separating the descent from the trees and the recorded history, by and large, is still a mystery.

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Riddle three: what is a virus?

In the case of humans, and indeed with most modern animals and plants, you can at least roughly draw a connection with evolutionary ancestors. Virologists cannot boast of this. In fact, science still does not understand what a virus is.

The fact is that these microscopic acellular parasites do not fit into the system of the living world at all. All living things known to us consist and come from cells. The virus also exists only with the help of cells: it needs a host to reproduce itself. If all cells suddenly disappeared from the planet, the viruses would turn into meaningless bubbles of proteins and DNA, incapable of any biological functions.

How did such a strange form of matter exist? There are two main versions

The first version: viruses are runaway genes. Such a scenario is not hard to imagine. In our genome, there are elements called transposons that can cut themselves out of one part of the genome and insert into another. Sometimes these "mobile genes" take with them other pieces of DNA that are in the neighborhood. It is assumed that billions of years ago, one of these "mobile genes" accidentally assembled in one set the minimum set necessary for independent existence: on the left, for example, there was a "copying machine" needed to reproduce DNA, and on the right - a "penknife" with with which you could get into a new cell. From that moment on, the gene turned into a virus and began to evolve separately from the parent organism.

Second version: viruses are simplified cells. A number of scientists today are inclined to this version, primarily due to the discovery of a number of giant viruses comparable in size to cells. According to this version, viruses may have once been cellular organisms - for example, bacteria. These bacteria have learned to parasitize on other, larger cells. Gradually, they got rid of everything unnecessary, including their own "cellular equipment" - and thus turned into viruses that retained only a few genes and "tools" needed to infect.

This hypothesis is supported by historical precedent. Something similar happened with mitochondria - "power stations" that make up our cells.Once they were bacteria, but then they entered into an alliance with larger cells, lost their independence and today they are an integral part of them.

As with the origin of life, the history of viruses is lost over the centuries. Viruses do not have bones or shells, they do not leave fossils or traces in sedimentary rocks. It is possible that viruses appeared independently (possibly in different ways) several times. It is almost certainly known that all living organisms originated from a single cell. Whether this applies to "semi-live" viruses is still unknown.

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Riddle four: why do we need sleep?

We spend a third of our lives in a dream - and at the same time we absolutely do not understand why. We know something about what happens in a dream, and partly why a dream could appear. But science cannot yet answer the question of why sleep is so necessary.

Circadian rhythms in general and sleep in particular are obviously associated with the rotation of the Earth around the Sun. Whatever the characteristics of the animal, for almost any of them there is a time of day when it is safer to do nothing, but just sit quietly and not stick out. It is quite logical that sleep could have appeared as a way to save energy in this "standby mode". The rest of the sleep functions - for example, processing and hardening memory - probably appeared as "add-ons" to this mode.

But this theory does not at all explain why sleep is so necessary. The scientifically documented record for intentional sleep deprivation (without the use of stimulants) is 11 days and belongs to the American Randy Gardner. Even such a not-so-impressive record could end in disaster: in 2012, a Chinese football fan who had watched Euro 2012 all night long died of a sleepless marathon of similar duration. Diseases that damage sleep mechanisms are extremely dangerous. An incurable hereditary disorder called Fatal Familial Insomnia speaks for itself: After the onset of symptoms, patients do not live even a year.

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Are there animals that do not sleep? This question was asked by scientists from the University of Wisconsin at Madison. Having considered the available data, they concluded: there is not a single clearly and unequivocally proven case of the existence of a "sleepy" animal to date. This does not exclude this possibility: the authors emphasize that data on sleep for most species are extremely scarce.

Nevertheless, the available information is sufficient for a fairly unambiguous picture: neither people, nor rats, nor even flies with cockroaches can live without sleep. Everything indicates that sleep is the same universal property of a living thing as breathing or heredity. But if the meaning of the latter is obvious today, then scientists will have to sweat a lot over the role of sleep.

What does a fly dream about?

New technologies have significantly advanced our ability to study sleep in other species. For example, modern equipment allows you to shoot something similar to an electroencephalogram … from a sleeping fly. In a study last year, scientists at the University of Queensland in Australia showed that flies not only sleep, but also have different sleep phases - just like ourselves. These phases vary in depth and alternate during the night, with the time for "deep sleep" increasing if the flies get very tired. Generally speaking, fly sleep is so similar to ours that scientists are discussing with might and main the use of fruit flies as a model for studying abnormalities that are characterized by sleep disturbance.

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Riddle five: what is "I"?

The last mystery that today's biology is breaking down is also associated with nervous activity, but much more complex than the sleep of Drosophila. Consciousness is such a complex and difficult to define process that for a long time a person arrogantly defined it as his own unique property.

Today, the uniqueness of human consciousness is a philosophical rather than biological question. It is indisputable that a person has reached unprecedented heights in the development of his intellect.But is there something qualitatively new in the structure and functioning of our brain? Most likely no. Dogs have emotions, monkeys can count, and dolphins even have a semblance of language with grammar and cultural differences in different parts of the world. Studying animals, we intuitively understand that some of them are at least remotely aware of their own existence. But we still do not understand at all what exactly is behind this awareness. Simply put, we do not know what consciousness is.

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In recent years, neuroscience has reached unprecedented heights. We have a good idea of ​​how nerve cells work, how they are activated or suppressed, and how they interact with each other. We know what changes in the composition of these cells during learning and memory formation. We know which parts of the brain are responsible for a particular behavior.

But knowing that the prefrontal cortex is somehow connected with social interactions, and the neurons in it bombard each other with special molecules and electric fields, does not mean at all to understand how one gets from the other. Today, scientists are making the very first attempts to simulate the operation of the simplest neural networks: the existing data can uniquely describe the "consciousness" of perhaps jellyfish. Science is not yet able to "hack" the human consciousness, no matter how much science fiction lovers want it.

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