Finally, after more than two months after the founding of this blog, I can post my first PaleoStoria. I must say I'm a bit 'excited, we hope to ear with clarity and without boring, because, being quite complex issues, unfortunately the post will be of considerable length. If you find them boring or too long, please let me know in the comments. For the first
PaleoStoria I chose a topic of great importance, both from an evolutionary point of view, and, above all, from a cognitive point of view. I think it's enough counterproductive to talk about complicated issues if you do not have certain basics. I could talk about bones, locomotives special adaptations, behavior, origin of certain anatomical structures, etc. .. But without first having explained things, the risk that certain notions for granted is very high. And, because what interests me is the look especially popular, I prefer starting from the base. For this reason, my PaleoStorie follow a fairly well-defined line of reasoning, using arguments that gradually becoming more complex. The fact that the increase in complexity also follows the chronological history of life on Earth and its evolution, will prove very helpful in understanding and narrative, and often the reader's task easier. In this first
PaleoStoria referred to as one of the fundamental concepts of the history of life on Earth: the origin of the body .
But what is a body? I will you ever wondered?
In general terms, we can say that a body is an aggregate of cells that work together to build and keep alive a larger whole, often turning different functions and specifications, and coordination so that each "give a hand" to the survival of 'whole.
One of the fundamental properties of the body is then co-ordination between different cells, their specificity and the fact that not all work for themselves but for the whole body that make up their own.
This distinction is crucial: a cluster of cells is not a body if they do not cooperate for the survival of the whole.
If, for example, take a colony of bacteria and extract from it some of these bacteria, we certainly find ourselves with a smaller colony, but if we extract the cells from a body of a human being or any other body with body, be the risk of being left with a dead body is by no means negligible (obviously depends on which cells are extracted).
A body is so much more than an aggregate of cells. One could say that it represents a kind of society, in which people with different abilities will pool their talents to make the most of the entire corporate structure. And most important, despite continuous cellular changes (the lifetime of a cell varies widely, from a few days to several years) your body continues to live. Despite several generational changes, "society body" goes on without trouble, thanks to precise rules and the innate spirit of cooperation that characterizes its inhabitants, the cells.
The body, in essence, is a very serious and wonderfully perfect and damn more complicated than simple clusters of cells.
For our distant relatives would evolve from unicellular forms to a corporeal creatures, their cells had to learn to collaborate, communicate with each other to join. All through new mechanisms, to equipment and methods ever used.
So if the level of complexity of the body is immensely higher than that of simple cell clusters, as has been possible to reach such complexity? When he grew the body? How? And most importantly, why?
The answer to the question about when the body is formed from a concept often overlooked, especially the superb species Homo sapiens: a large part of the history of life on Earth is the story of unicellular organisms. Not only do they have developed, but much of the first multicellular organisms, but still represent a big slice (much more than their "relatives" multicellular) of the biotic component of our planet. Virtually everything in the next post I will talk about (that of multicellular organisms) inhabiting the Earth from a small fraction of time.
How do we know this? Easy, fossils.
From fossils we know that life on Earth probably appeared around 3.5 billion years ago, and up to 600 million years ago, more or less, the only organisms on our planet were unicellular. Layers are older than 600 million years, in fact no trace fossils of complex life.
Soon after though, and apparently suddenly appear a multitude of fossils of animals with real bodies, some very specialized, others simple. But in any case, bodies, bodies with a capital.
As a sort of explosion, in a short time you spent a lifetime in a single cell was "body", more or less complex.
the question "when?" Respond well fossils 600 million years ago (Precambiano). Understanding how and why this happened, it's definitely a different story.
Now, to understand how we had originally multicellularity soa makes me ask you just so special and efficient body.
What holds together a group of cells, either a jellyfish or a complex human organ? What makes them able to communicate?
The answer is quite long and complex, and requires fairly detailed knowledge of anatomy and cell biology. But we try to simplify a little 'things.
feature common to all multicellular organisms, both vertebrates and invertebrates, plants or simple clumps of cells, is that they possess molecules that occupy the empty space between one cell and another. These molecules are varied, and often most of the specific properties of a certain set of cells is derived from molecules which they are held together, and how these cells are placed.
In animals, one of these special substances is collagen, a protein that alone is more than 90 percent of all proteins in the body. Thanks to collagen, our cells are connected to each other, that they can interact and communicate.
In addition to joining the cells, these molecules (I repeat, there are many and varied) made possible the interactions between different cells. Some are so specialized (select the link, just by binding to molecules of the same type) that give the cells the wonderful property of being able to bind only to their own kind. So, ensure that cells are able to be positioned at the sun between them, so that the skin cells to bind to cells in the skin, which bind to the eye than those in the eye and so on.
These molecules, cells also provide an efficient system of communication so that each knows when to replicate, creating molecules bind, die, etc. ..
Ultimately, it is all of these molecules and their interactions with the cells that allow the existence of the body.
Well, now that we have an idea of \u200b\u200bwhat a body and what allows it to be, we can try to understand how it originated.
But first, I want to bring to your attention a great scientific experiment that will prove useful to our inquiry and absolutely enlightening.
Henry Van Peters Wilson was one of the greatest biologists of the twentieth century. During his years at the University of North Carolina, he taught biology to some American students, who will later become some of the brightest minds of genetics and cell biology.
From a young age, Wilson decided to dedicate his life to the study of sponges, considered by him (in hindsight) some of the most interesting animals from a biological standpoint.
Sponges are very primitive organisms: their body is essentially composed of a matrix is \u200b\u200bnot alive, usually composed of silica or calcium carbonate, and a set of more or less specialized cells, held together by collagen. Although not particularly complex, the sponges have all the requirements to be considered in all respects bodily organisms.
He was at the beginning of the twentieth century the good Wilsons made a fantastic experiment with sponges, in an attempt to study them in detail: the specimens taken and passed them through a sieve, reducing them to a pile of broken cells. Later, he took these single cells and placed on a slide for study. With great satisfaction, that he soon began to move individual cells on the slide and, with great speed, came together in one body! At first, they formed a chaotic mass of cells and then in a short time, they organized and gave life back to a sponge! Wilsons had observed in the direct formation of a body!
This experiment showed how the sponges were absolutely amazing animals, and especially how the structural properties of the body are given their own collagen and interactive capacity between the various cells.
The origin of the body then has to be found in the source material and cell properties essential for the establishment of the "body"?
Until recently it was thought that the answer was "yes", because the study of genes of organisms "without body" was certified the absence of those materials that make the cells able to participate, communicate, etc.. So, it seemed clear that the origin of the body were connected with the appearance of such property.
Scholars, however, had not yet come to terms with the strange single-celled organisms: the coanoflagellati.
A study published by Nicole King, a researcher at the University of Berkeley, California, showed how coanoflagellati are present in different molecules homologous to those of cellular organisms, such as collagen or there different types of molecules that enable cell communication. In short, the coanoflagellati have all the means possible to aggregate and form bodies. Still, they are single-celled organisms.
And subsequent studies, reported that some of these molecules were also present in some bacteria (including streptococci), but which were used to other functions, metabolic often.
The fossil record tells us that up to 600 million years ago all were single-celled organisms on Earth. Then all of a sudden, in a time fast enough (40 million years), bodies appear everywhere: plants, animals and fungi. Yet, as demonstrated by Nicole King, life had long since to form the basis for bodies.
Why it all happened so quickly and suddenly? Because, while being able to "merge" for some time, preferring to remain single-celled organisms?
To answer this last question, I will quote once again an experiment.
Martin Boraas and his colleagues, in a admirable experiment in cell biology, trying to understand what factors may have facilitated the development of the body: they took a unicellular alga (which meet the requirements for the body, but using them in a different way) and let it develop in the laboratory for several generations.
Then, at some point, they introduced an agent of disorder, a predator, able to incorporate the individual and algae to feed on them. In less than two hundred generations, the algae responded by evolving into a cluster of one hundred cells, that number dropped gradually and reached steady at eight per clump (the number eight turned out to be more balanced, because it allows the individual clusters to be large enough not be counted from the predatory and small enough to live on their own, without too much energy). By removing the predator, Boraas and his colleagues went on to say that the algae reproduce to form individuals of eight cells each.
In essence, through the introduction of a predator, a unicellular organism gave rise to a multicellular organism in a very short time.
The experiment did advance the theory that the development of the body evolved when the single-celled organisms found new ways to predict or to avoid being prey. Having a body would be an advantage because it allowed not to be eaten, given the large size, is able to feed on smaller creatures. It also allows you to cover distances more.
all makes sense, but does not answer our question: why has not developed before?
Perhaps the problem was to find the energy needed to keep alive a body, since over a large body is most in need of food and energy (especially if formed from collagen, which needs a lot of oxygen to synthesize).
Early in the history of the Earth, at a time when life began, Earth's atmosphere contained little oxygen, infinitely insignificant compared with the amount contained today. And, probably, too little even to allow the development of the body.
However, about a billion years ago, the oxygen level began to rise, as demonstrated by chemical analysis of rocks from that period.
And perhaps because of this, took the spark for the formation of bodies: for billions of years, single-celled organisms had evolved continuously developing new techniques for feeding and interacting with the environment around them. In doing so, they had developed, albeit for different purposes, all the requirements to form the bodies. And, moreover, were evolving new forms of predation, learning to eat each other. There was already
all means to form a body, there were already reasons to do it, but there was still one small detail: the oxygen to supply the energy needed to sustain the body.
And when the level of oxygen in the atmosphere reached the right place, like a pressure cooker office for some time, corporeality exploded into a myriad of amazing shapes. All of a sudden, the earth was filled with bodies everywhere. And from there, it was a different story ..
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Bibliography:
N. King, 2004, "The Single Cell Ancestry of Animal Development", Developmental Cell, 7 , pp. 313-325
MEBoraas, and J. DBSeale Boxhorn, 1998, "by Phagotrophy to flog Selects Colonisl for Prey: A Possible Origin of Multicellularity", Evolutionary Ecology, 12, pp. 153-164
Clipboard course Phylogeny Animals of Professor Robert Penn, Unimi.
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