There are many biologists, zoologists, botanists and other life-scientists who study every aspect of our living environment, including all known microorganisms, fungi, animals, and plants, and their surroundings. Scientists also observe human behavior; what causes us to be the way we are, and to do the things we do.
Since the beginning of life on earth 3.5 billion years ago, the struggle for survival has created an evolutionary process of growth and change.
Every living thing, from bacteria to plants to humans, grows and changes in a unique way. This happens because of two things. One, there is a set of genetic instructions contained in each cell of an organism that describes, chemically, what the animal or plant will generally look like, and how it will function over time. The other way a creature grows and changes is through learning and experience in the tough world of its environment.
Surprisingly, all living things have evolved from a single common ancestor, the first living organism on earth. We are all related to the microbes, plants, fungi, and animals from which we are descended.
Remarkably, this first organism was able to make copies of itself, thus passing on to its offspring the same ability. After a time, there were millions of similar organisms all struggling to adapt to their surroundings, and those that succeeded were able to survive and make copies of themselves just as their parents had.
But there is a twist. During the copying process, genetic irregularities can occur that slightly change what an off-spring looks like or how it functions. These anomalies, known as mutations, are usually detrimental to an organism. But sometimes the change is beneficial, providing a slight adaptive advantage, especially when the environment in which a creature lives undergoes a dramatic change. The new off-spring may have just the right mutation to adapt to the changing environment. Over time, successful mutations tend to result in the creation of new organisms.
This genetic process of continual growth (replication, reproduction) and change (mutation) has resulted in the huge variation of life on earth, from single-celled creatures, to insects, birds, plants, and animals, including humans.
Charles Darwin, famous 19th century biologist, was the first to correctly identify the process of EVOLUTION in living things. He called it NATURAL SELECTION because some creatures are selected over others for their ability to successfully adapt to their environment; and also to distinguish between the breeding of domestic animals by farmers and others, known as artificial selection.
The discovery of evolution, by means of natural selection, is one of humanity’s greatest achievements. It competes with religion and philosophy as a way of verifying the origins, or creation, of humankind. For this reason, the contemporary philosopher Daniel Dennett and others have referred to Darwin’s discovery as a ‘dangerous’ idea.
Remarkably, Darwin was able to describe natural selection without the benefit of knowing about genes. Famously, an account of Gregor Mendel’s genetic experiments lay unopened on Darwin’s desk at the time of his death. Since then, in little more than a century and a half, we have not only modeled the DNA molecule (Crick and Watson), but mapped the entire human genome (Craig Vintner, et al.).
Darwinian evolution is also an idea that is counter-intuitive. The ‘workings’ of natural selection are not always obvious, largely because there is no single ‘director’ in charge. Evolution is a process without a set of plans. And it has no specific motivation or intention.
As biologist and environmentalist Edward O. Wilson points out in his Pulitzer Prize-winning book On Human Nature, one of the challenges of human evolution is that there isn’t a programmed or prescribed set of rules to tell us what to do, or how to do it. There is no original or intrinsically shared purpose among humans. Each of us, as individuals, must develop his or her own sense of purpose in life.
Henry David Thoreau, the transcendentalist philosopher, author, and naturalist was the first American to champion Darwin’s ideas. Others around the world felt its impact, but it took almost 150 years before the general public began to fully appreciate the enormity of Darwin’s discovery.
An English biologist (whose name I can’t recall) contends that the answer to any question about life is: natural selection. When I first came upon this quote, like others, I was skeptical. Over the years, I have found it to be surprisingly test-worthy.
Since the discoveries of Darwin, Mendel, and the rest, it has been assumed that changes in the human genome are caused by genetic inheritance alone. But it has slowly become evident that genes are able to respond directly to the environment as well. Remarkably, recent studies in the field of epigenetics have shown that stress, diet, behavior, toxins, and other external factors act as triggers that chemically switch genes off and on at strategic times and locations within the body. On average, about one percent of epigenetic changes reach the chromosomes containing the ‘sex’ genes, which is enough to significantly alter the genome of the next generation.
While Darwinian evolution tends to occur over many generations, with mutations acting as the agents of change, epigenetic changes, caused by environmental factors, are inherited within a single generation. In general, it is easy to hypothesize that we are witnessing an increase in the rate of genetic evolution due to an increased population entwined with an environment that is changing more and more rapidly every day.
Another form of evolutionary CHANGE, that Darwin wasn’t aware of, is SYMBIOSIS. A special symbiotic relationship occurs in nature when two very different kinds of creatures form a lasting partnership. This partnership sometimes results in a new species.
For example, when a small single-celled organism tries unsuccessfully to invade and kill-off another single-celled creature, and neither is able to destroy the other, they may decide to ‘work together’, resulting in the creation of a new organism that combines qualities of both.
Our human body cells (soma cells) have evolved over millions of years in exactly this way. Each of our body cells is a ‘factory’ of living ‘machines’. At different stages in our biological history, an organism has invaded our body, and when failing to destroy a cell, stayed on as an ‘uninvited guest’, forming a partnership with the host cell. These invading organisms brought with them new attributes that made the human cell more powerful.
Over time, an increasing number of these ‘uninvited guests’ became permanent residents, resulting in a human body cell that is very efficient in doing the different jobs that are required to maintain our health and well-being. These inter-cellular residents, known, collectively, as organelles, include the nucleus, mitochondria, ribosomes, and several others.
Indeed, the human body itself is a classic example of symbiosis. A variety of microscopic organisms form bacterial gardens that take up residency in our mouths, guts, and colons. These millions, trillions, and even quadrillions of friendly bacteria help us to digest our food and to destroy bacterial enemies. Without them we could not function. Our entire bodies are living habitats.
(I highly recommend any of a variety of books by microbiologist Lynn Margulis, who is responsible for the pioneering and widespread popularity of symbiosis as an agent of evolutionary change.)
In addition, there are other kinds of long-lasting partnerships that don’t result in a new organism or species. These are common among plants and animals, including bees and flowers, insects and birds, trees and fungi, and many others.
Bees drink nectar produced by flowers, while flowers, which are stuck in one place, rely on bees to visit them in order to carry their pollen from one flower to the next. This relationship nourishes the bees, and produces the next generation of flowers. Both appear to be content with the arrangement. Another kind of partnership involves birds and insects. Birds like to eat insects. But a bird will not eat an insect that lives in its nest and helps keep it clean. Both the bird and the insect find the arrangement friendly and profitable. A tiny fish may inhabit the mouth of a large fish for its entire lifetime, both of which benefit from the partnership. Nature is filled with many such examples.
In general, symbiosis creates new, complex, species rather quickly, sometimes within days, while natural selection creates many diverse kinds of creatures over a period of hundreds or thousands of years; although microorganisms and small insects may evolve much quicker.
When a species of bacteria, fungi, animals, or plants successfully adapts to its surroundings, the species, in turn, modifies its environment. Every species coevolves with its environment, shaping and changing itself and the Earth.
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