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| Evolution at Work |
Evolution at Work
There are four active mechanisms that lead to the evolution of species.
Mechanism #1: Competition
The mechanism of competition corresponds to Darwin’s ‘survival of the fittest’.
Plants compete for water, sunlight, and the attention of insects to pollinate them.
Animals compete for food, territory, and mates. Individuals have to compete with members of their own species, as well as other species for the limited life-giving resources they can find. In stable conditions, the growth potential of every species ensures that there are always more offspring produced than can possibly survive. Only the toughest, luckiest, and most adaptable individuals make it to adulthood. The average characteristics of a species become precisely the characteristics that maximize an individual’s chances of survival under the prevailing conditions.
In many species, it has been observed that individuals sometimes sacrifice themselves to protect others in their family, or social group. How can such altruistic behaviour exist if evolution is based on competition for survival among individuals? In the latter part of the 20th century the competition mechanism was modified to read ‘survival of the fittest genes’. In most cases, survival of the fittest genes still corresponds to survival of the fittest individual. But in a familial group, all the individuals share common genes. So if the survival of the whole group is threatened, it is an effective strategy for a few individuals to sacrifice themselves in an effort to protect the whole group. A mother may give her last morsel of food to save her children. A soldier may face an invading army to protect his city. Individuals can give their lives to help to ensure the survival of their own genes.
Mechanism #2: Environmental changes
According to geological evidence, the climate on Earth changes over time. Most of the changes are cyclic and occur gradually over thousands of years. At any location on Earth there have been periods of drought, periods of heavy precipitation, periods of relative cold, and periods of relative warmth. Occasionally, major events such as volcanic eruptions or asteroid impacts produce rapid changes in climate.
Every change in climate provides plants and animals living in those regions with fundamental challenges. Will they still be able to compete successfully for food and water? Will they still be able to reproduce? Will they still be able to survive? As the environment changes, the old average characteristics are no longer the optimal values. Individuals with some extreme characteristics are now more suited for survival. The giraffe with a longer neck will be able to reach the higher leaves on a tree. It will tend to survive and produce offspring with longer necks. The camel that can walk farther after drinking less water will have a greater chance of surviving when the water supply is dwindling. The offspring of such a camel will tend to inherit this same characteristic. The average value of inherited characteristics in a population will gradually shift as climate change continues.
Note that the characteristics of individuals do not change, but individuals that already have advantageous characteristics in the new climate are more likely to survive and produce offspring. Even individuals with extreme characteristics may not be able to survive if climatic conditions change too quickly. The species may become extinct. Mechanism #3: Mutations
Occasionally during the division of a cell, an error occurs in the duplication of DNA and a mutated gene is created. If the mutation is not fatal, it is passed on in the altered DNA to all future generations of that cell. Mutations can be caused by radiation passing through a cell, by the cell absorbing novel chemicals, or by a random error in the complex process of cell division. When a mutation occurs in an egg or sperm cell, the mutation is passed onto future generations of that individual.
An organism can cope with some minor genetic errors. There are two copies of each DNA strand; when one DNA strand is altered there is a backup DNA strand from the other parent that can sometimes be used to correct faulty coding. The impact of dominant versus recessive genes and the specific location of a genetic mutation can also affect a cell’s ability to survive.
The process of life is extremely complicated and one would expect most major genetic errors to produce fatal results. However, the growth potential of every species ensures that there are always more offspring produced than can possibly survive. On a rare occasion (perhaps one in a million, or one in a billion), a mutation leads to a modified characteristic that enhances an individual’s chance of survival.
Just a small change – such as slightly improved night vision – could lead to the difference between surviving, or being eaten by a predator. Individuals with improved night vision would then have a greater probability of producing offspring, and those offspring would also inherit that improved night vision. Over several generations, that modified characteristic could become the new normal characteristic for the whole species population.
Note that mutations lead to modifications of existing characteristics, or the addition of new features. No single mutation can replace a complicated organic structure with a different complicated structure. Evolutionary changes due to mutations occur a bit at a time, and tend to be add-ons rather than replacements.
Mechanism #4: Co-evolution and punctuated stability
Every species is part of a larger ecosystem. The lives of many species are linked together in an environmental niche. When the climate is stable, the characteristics of all the species tend to evolve towards stable values that maximize each species opportunities for survival in that niche. As long as the conditions remain stable, the characteristics of these linked species tend to remain relatively stable as well. Such a period of stability may last for several million years. However, if the stability of the environmental niche is altered then a rapid spurt in evolution tends to occur in all the related species at the same time.
The stability of an environmental niche can be altered by changes in the climate, by a mutation that alters an important characteristic of just one of the species, or by the introduction of a new species from outside the system. All the species in the niche will then evolve until a new equilibrium is reached.
In summary, there are at least six preconditions necessary for evolution to occur: the role of DNA in the reproduction of cells, the capacity for rapid population growth, genetic variations within a family, genetic variations across a population, a period of time spanning at least hundreds of generations, and the input of energy from an external source. There are four main mechanisms that actually drive the process of evolution: competition for resources, changes in the environment, mutations, and the co-evolution of species.
There are four active mechanisms that lead to the evolution of species.
Mechanism #1: Competition
The mechanism of competition corresponds to Darwin’s ‘survival of the fittest’.
Plants compete for water, sunlight, and the attention of insects to pollinate them.
Animals compete for food, territory, and mates. Individuals have to compete with members of their own species, as well as other species for the limited life-giving resources they can find. In stable conditions, the growth potential of every species ensures that there are always more offspring produced than can possibly survive. Only the toughest, luckiest, and most adaptable individuals make it to adulthood. The average characteristics of a species become precisely the characteristics that maximize an individual’s chances of survival under the prevailing conditions.
In many species, it has been observed that individuals sometimes sacrifice themselves to protect others in their family, or social group. How can such altruistic behaviour exist if evolution is based on competition for survival among individuals? In the latter part of the 20th century the competition mechanism was modified to read ‘survival of the fittest genes’. In most cases, survival of the fittest genes still corresponds to survival of the fittest individual. But in a familial group, all the individuals share common genes. So if the survival of the whole group is threatened, it is an effective strategy for a few individuals to sacrifice themselves in an effort to protect the whole group. A mother may give her last morsel of food to save her children. A soldier may face an invading army to protect his city. Individuals can give their lives to help to ensure the survival of their own genes.
Mechanism #2: Environmental changes
According to geological evidence, the climate on Earth changes over time. Most of the changes are cyclic and occur gradually over thousands of years. At any location on Earth there have been periods of drought, periods of heavy precipitation, periods of relative cold, and periods of relative warmth. Occasionally, major events such as volcanic eruptions or asteroid impacts produce rapid changes in climate.
Every change in climate provides plants and animals living in those regions with fundamental challenges. Will they still be able to compete successfully for food and water? Will they still be able to reproduce? Will they still be able to survive? As the environment changes, the old average characteristics are no longer the optimal values. Individuals with some extreme characteristics are now more suited for survival. The giraffe with a longer neck will be able to reach the higher leaves on a tree. It will tend to survive and produce offspring with longer necks. The camel that can walk farther after drinking less water will have a greater chance of surviving when the water supply is dwindling. The offspring of such a camel will tend to inherit this same characteristic. The average value of inherited characteristics in a population will gradually shift as climate change continues.
Note that the characteristics of individuals do not change, but individuals that already have advantageous characteristics in the new climate are more likely to survive and produce offspring. Even individuals with extreme characteristics may not be able to survive if climatic conditions change too quickly. The species may become extinct. Mechanism #3: Mutations
Occasionally during the division of a cell, an error occurs in the duplication of DNA and a mutated gene is created. If the mutation is not fatal, it is passed on in the altered DNA to all future generations of that cell. Mutations can be caused by radiation passing through a cell, by the cell absorbing novel chemicals, or by a random error in the complex process of cell division. When a mutation occurs in an egg or sperm cell, the mutation is passed onto future generations of that individual.
An organism can cope with some minor genetic errors. There are two copies of each DNA strand; when one DNA strand is altered there is a backup DNA strand from the other parent that can sometimes be used to correct faulty coding. The impact of dominant versus recessive genes and the specific location of a genetic mutation can also affect a cell’s ability to survive.
The process of life is extremely complicated and one would expect most major genetic errors to produce fatal results. However, the growth potential of every species ensures that there are always more offspring produced than can possibly survive. On a rare occasion (perhaps one in a million, or one in a billion), a mutation leads to a modified characteristic that enhances an individual’s chance of survival.
Just a small change – such as slightly improved night vision – could lead to the difference between surviving, or being eaten by a predator. Individuals with improved night vision would then have a greater probability of producing offspring, and those offspring would also inherit that improved night vision. Over several generations, that modified characteristic could become the new normal characteristic for the whole species population.
Note that mutations lead to modifications of existing characteristics, or the addition of new features. No single mutation can replace a complicated organic structure with a different complicated structure. Evolutionary changes due to mutations occur a bit at a time, and tend to be add-ons rather than replacements.
Mechanism #4: Co-evolution and punctuated stability
Every species is part of a larger ecosystem. The lives of many species are linked together in an environmental niche. When the climate is stable, the characteristics of all the species tend to evolve towards stable values that maximize each species opportunities for survival in that niche. As long as the conditions remain stable, the characteristics of these linked species tend to remain relatively stable as well. Such a period of stability may last for several million years. However, if the stability of the environmental niche is altered then a rapid spurt in evolution tends to occur in all the related species at the same time.
The stability of an environmental niche can be altered by changes in the climate, by a mutation that alters an important characteristic of just one of the species, or by the introduction of a new species from outside the system. All the species in the niche will then evolve until a new equilibrium is reached.
In summary, there are at least six preconditions necessary for evolution to occur: the role of DNA in the reproduction of cells, the capacity for rapid population growth, genetic variations within a family, genetic variations across a population, a period of time spanning at least hundreds of generations, and the input of energy from an external source. There are four main mechanisms that actually drive the process of evolution: competition for resources, changes in the environment, mutations, and the co-evolution of species.
