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The "terrible" mystery of evolution

New insights into the way the earth was filled with flowers

flower garden Photo: shutterstock
flower garden. Photo: shutterstock

There are about 350 "seed-covered" plants in our world, species of plants with flowers that make up more than 90% of all plant species. In contrast, only about 1000 angiosperm species, most of which are conifers.
The importance of flowers to man and the environment is great and enormous. Without flowers, most of the agricultural crops will be lost, including plants for feeding farm animals. Flowering plants are one of the most important factors in removing carbon dioxide from the atmosphere. Without a doubt, the flowers decorate our world and are an inspiration for works of art and culture.

But the appearance of flowers in the world is a mystery even today. Darwin described the appearance of flowering plants as "an abominable mystery" or "a most perplexing phenomenon". Twenty years after he published "The Origin of Species" there were still aspects of evolution that bothered him. One of the sides or one of the main puzzles was the development of the flowers.

Flowering plants belong to the large and diverse group of "angiosperms", that is, those that produce a fruit inside which the seed is hidden. Darwin's concern was that the earliest appearance of seed coats was only in the Cretaceous, that is, about 100 million years ago, when flowers appeared as if at once in a variety of shapes and sizes. That is, there was an eruption of species immediately after the appearance of the ancestor.
Darwin described evolution as a "gradual process by means of natural selection", but the sudden appearance of a large variety of species in a new group does not correspond to the assumption of the gradualness of the process. Although according to new research, the flowers developed in a gradual process (and not in a jump), but several puzzles still remain - how and when did the flowers develop and what made them so successful?

Darwin was an expert in locating and identifying origins and origins. His insights helped to build a framework for how species were created and he was convinced and determined that the process was gradual and slow. According to him "natural selection works slowly and collects positive changes, it cannot produce sudden adjustments, it only works in small and slow steps".
"As natural selection acts solely by accumulating slight, successive, favorable variations, it can produce no great or sudden modification; it can act only by very short and slow steps,” (from the origin of the species).

Despite his determination, Darwin was aware of outliers and yet the spermatozoa were a source of frustration for him. Seed pods or flowers did not exist for most of history. Those who preceded them were gymnosperms such as ferns and cycads that grew in evergreen forests and over the ages most of them were "replaced" by the conifers and then the flowers appeared.

Researchers in the 19th century emphasized the huge variety of flowers called "higher plants" or (dicotyledons) whose "sudden appearance" in the Cretaceous era gave them the basis for attempts to embarrass Darwin and attack his explanations of evolution.

Darwin offered a solution to the mystery by saying that flowers evolved slowly and gradually in remote areas (those not yet explored by scientists). In the middle of the Cretaceous, an "opportunity" was created that caused them to spread rapidly from their habitat to the whole world.
According to him: This is how European and American researchers get the mistaken impression as if all the flowers developed at the same time. Darwin was aware that he had no evidence to back up this assumption and therefore described it as insufficient. Over time, his hypothesis was proven to be partially correct, when flower fossils were discovered in China that existed tens of millions of years before the Cretaceous, and later such fossils were also discovered in Europe and North America. That is, the appearance of the flowers much earlier than what was known moderates Darwin's problem and confirms the theory of gradual development in evolution.
"Darwin's problem" may have been solved, but not so the riddle posed by the tremendous and spectacular variety of flowers. Perhaps a partial solution to the problem is found in New Caledonia, where a plant called Amborella was discovered. A thorough study of the plant showed that it is the last survivor of one of the early branches of angiosperms. That is, its proximity to existing flowers is similar to the proximity of the duck (platypus) to mammals, so the umbrella plant can perhaps reveal to us how flowers evolved.

According to the study of the umbrella's genome, it turned out that the first flowers seem to have evolved from the seedless species that were common all over the world, the first of the seed coats probably appeared when the ancestor of the umbrella underwent duplication of its entire genome about 200 million years ago. ("Genome duplication" happens when a creature or plant accidentally "acquires" an extra copy of each gene during sexual reproduction. The extra copy gives the creature the possibility to develop additional traits that have a survival advantage). The plant with the genetic addition developed a new structure - a flower.

In the 19th century, a French biologist (Gaston de Saporta) supported Darwin in his claim that his assumption about the gradualness of evolution is generally correct, but it is possible that there will be exceptions, such as the flowers that evolved together with pollinating insects, which resulted in speed and enormous diversity.

But the theory has encountered problems nowadays. Some argue that since, according to fossils, the first flowers were simple (unattractive to pollinators), it may have been the exposed seeds that produced flowers. Later the large and "attractive" flowers that attract insects appeared, then the seed pods were already diverse and numerous.
In 2009, researchers from a university in the Netherlands claimed that "since the flowers are more fertile and grow faster than the seed pods, it is no wonder that they win the competition for food and therefore their distribution is wider." They later state that a finding that supports the claim was observed in flower fossils in which more transport tubes (arteries) are visible, which gave the flowers the opportunity to supply more water to the leaves. More water allows more assimilation (photosynthesis) which allows for faster growth.
At the same time, the researchers say that "there is no simple explanation for the enormous diversity and ecological control of the flowers." It is possible that many different factors acted together and separately. It must be assumed that in different climate zones different factors acted on the distribution of flowers and their diversity.

There are those who claim that success should be measured not only by the number of species and the wide distribution, since in the north conifers "dominate" in large areas that also slide into temperate areas, it is possible that in these areas the soil is too poor for the flowers to be able to take advantage of their advantage. The question arises, how is it that out of 350 species, no ones have developed that are able to overcome the problem of poor soil and compete with conifers in the north?
And the mystery returns again.

Now, after all this, the question remains, can the flowers "tell" how and why they became so diverse?

Today, researchers and botanists have much better information and tools than Darwin had in his time, yet they still struggle to explain the enormous diversity and why, despite the diversity, the flowers were unable to take over large cold and northern regions of the world. It is possible that the fact that the mystery charms researchers will eventually lead to a solution, perhaps also because of Darwin's attitude to the problem in his writing "the abominable mystery...

12 תגובות

  1. Saying theories is the easiest, no one wants to deny: 'I've been alive for a billion years and I say it was one way or the other', so they say and people believe, like they believe in all the sects in the world! Be real and honestly search for the truth!!! You will find in the end!

  2. Sagi
    If there aren't many flowers, then there probably won't be many pollinators. In cold areas there are many flowers - alpine bloom is low but dense, and there are also many small flying insects.

  3. Is there the same activity of insects and other pollinators in the cold areas, which were not taken over by the flowering plants?
    In addition, coniferous plants shed their needles and cause soil acidity that does not allow the growth of other plants. Thus any forest may eventually become a coniferous forest.

  4. Snupkin
    Nice thought... In my opinion, the same limit you mentioned is reached much faster than you think. Throw some mustard seeds in the field and you will see that in a few years the whole field will be covered with mustard. The natural reproduction rate of most creatures is alarmingly high.

  5. In fact, in any system the entropy will increase until it encounters an obstacle, that is, the genetic diversity will increase until it encounters a factor that will perform selection on it (and eliminate the least suitable over time).
    Without a clear advantage for the shape, color, size or other variable of the flowers, the variety will increase more and more.
    For example, it is possible that the amount of insects was never really a limiting factor for the flowers (if there are more flowers then there will very quickly be more insects drinking nectar and all...), so a weak competitive pressure resulted in the continued increase in diversity.
    If anything, the pressure is in the opposite direction, the amount of flowers will limit the amount of insects that will survive.
    Just a thought…

  6. We know that, apart from natural selection, there are other types of selection. A good example is human choice. Every year there are new varieties of roses, dahlias and other flowers. And think about broccoli, cabbage, cauliflower, Brussels sprouts and kale - these are all artificial varieties of the same species.
    Therefore, I think it is logical that the selection of the insects will have a very strong effect on the competition between the flowers. Another thing that can accelerate the change is that a seed can move very far from its natural environment, and thus a new species can develop more easily (allopatric evolution).

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