The biological traits of living organisms are controlled by genes. The more complex an organism is, the more the number of genes that would be present in its genome, and the simpler an organism is, the fewer the number of genes in its genome would be. The genes in the body of living organisms are controlled and selectively expressed depending on a host of intrinsic factors. This is one of the reasons humans have the capacity to adapt to a wide range of environmental conditions and even pass the adaptive gene to their offspring. Thus, the offspring grow to become auto-adapted to the environment exemplifying a simple concept of evolution.
What is evolution
To a layman, evolution means the gradual development of something. But to a biologist, evolution is the gradual development of living organisms from simple types to more complex types. The simplest types of organisms are, therefore, known as the ancestors or the ancestral types. The environment of living organisms keeps change either naturally or due to the modification by the organisms themselves. The biological system of these organisms keeps trying to adjust accordingly in order to adapt to the changes in the environment. Those whose system has the program to adjust will eventually do so and keep thriving in the changing environment while others that do not have the natural means either physically migrate or gradually die off the population.
Organisms that are able to survive in a changing environment do not just develop the attribute. Such attributes either have been lying dormant within their systems and are only activated by the changes in the environment or a mutation to an already existing gene becomes advantageous in a way as to enable organisms to adapt to the environment.
There are two theories that support the concept of evolution:
Natural selection theory
The main proponent of this theory is Charles Darwin. He was able to come about the theory after series of observations during his expedition as a naturalist with HMS Beagle ship in 1831. Darwin eventually published the findings from his trip in a book titled 'Origin of Species' in 1859. In this book, the theory of natural selection was propounded.
According to the theory, organisms either naturally evolve to cope with changes in their environment or risk being gradually eased off from the population by the ones that are able to cope. The strong ones reproduce maximally and are able to pass on the survival gene to their offspring while the weak ones hardly contribute to the future generations and eventually die off from the population.
The surivival gene do not just develop all of a sudden. They have always been in the genome of the organisms, perhaps in a turned-off form. The change to the environment and the strive to adapt to it only make the gene to be turned-on. on the other hand, the quest to adapt might cause a beneficial, survival-confering-mutation of an already existing gene. Hence, the organisms without the survival gene are considered weak while the ones that survive are said to have evolved.
Natural selection at play
Mr Edward is visiting the hospital for the third time within a month based on the same health related issue. The drugs that have been prescribed by the Physician do not seem to be working, unlike before when any of these drugs would have effectively dealth with the pathogen. It may seems that the pathogen responsible for his health issue have developed multiple resistance to drugs.
Resistance to drugs by microbes happens by either of two ways:
- Natural selection: Natural selection works by selecting for survival genes in a population. When a drug is taken against a particular pathogen, the drug kills off the susceptible ones while the ones with resistance gene to the drug survives. Natural selection, thus, selects for this gene and makes it to multiply in the population. Consequently, the drug becomes ineffective against the population of the pathogen going forward.
- Mutation: Microbes generally multiply by dividing. During division, the genetic materials of the cell is replicated and shared into daughter cells. Errors sometimes occur during this replication and this can either be deleterious to the new cells or confer advantages on them. The sudden change to the genetic materials is referred to as mutation. Many issues of multidrug resistance have been linked to the mutation of the pathogen.
Jack has been dealing with the weed around his house by killing them off using a particular brand of herbicide at regular intervals. Within a few years, he noticed that the herbicide no longer deal effectively with the weed. He had no option but to do away with the herbicide he has been using for another brand of herbicide with different constituents entirely.
What it means is that the weeds have naturally evolved and become resistant to that particular herbicide. Natural selection selects for the few resistant genes within the population and the weeds carrying this gene thrives and multiply while those without the genes were killed by the herbicide.
Theory of use and disuse of organs
This theory, proposed by Jean Larmarck but now considered obsolete, was used to back the evolution theory for a long time. Lamarck believes that acquired characters can be passed on from parents to offspring. He opined that a more frequent and continuous use of an organ will go a long way in strengthening the organ while limited use of any organ will reduce its fitness. With time and in subsequent generations, used organs become more fit and effective in carrying out their specific functions while organs that are hardly used degenerate and become significantly reduced in structures. Such organs are referred to as vestigeal organs.
Evolution is a branch of biology that believes that organisms gradually develop from simple to more complex ones as future generations emerge. This belief is backed by theories that have been propounded by different scientists - the natural selection theory by Darwin and law of use and disuse of organs by Lamarck. In essence, every organism as they currently are have ancestors that were simpler in structure.
There are several evidence to support the theory of evolution. These will be discussed in my future posts.
Thank you for reading.