Biological Evolution Simple Definition and Examples
The biological evolution corresponds to the processes of modification and adaptation of the species over time .
The current diversity of living beings is the result of processes of transformation and adaptation of species to various environments, constituting biological evolution.
The main idea of biological evolution is that all living beings share the same ancestor. From there, the enormous variety of species that we found today arose. It can be said that evolution is the process by which modern organisms developed from ancient ancestors.
Until the mid-nineteenth century, the idea of creationism predominated. According to creationism, the species were created by a divine act, remaining immutable until today.
From the middle of the 19th century, the evolutionist theory began to gain strength. In this context, the ideas of Charles Darwin and Alfred Russel Wallace are the most consistent in explaining the evolution of living beings. Darwin affirmed that living beings, including man, descend from common ancestors, which were modified over time.
Currently, the theory of neo-Darwinism explains the evolution of living beings. It emerged in the twentieth century and represents the union of Darwin’s studies, mainly natural selection, with discoveries in the area of genetics, such as Mendel’s laws and mutations.
Evidence of biological evolution
Among the main evidences of evolution are the fossil record, the adaptation of living beings to their environments and the similarities between species.
A fossil is any vestige of a very old organism that was preserved over the years by natural means.
The study of fossils allows us to reconstruct the image of an already disappeared species and contributes to the study of the evolution of living beings. From the analysis of the similarities and differences between species, we can deduce the moment of their appearance and extinction.
Adaptation corresponds to the adjustment that all organisms experience in relation to the environment in which they live.
The adaptations are characteristics maintained in populations or species by natural selection ; they have a relative importance in the survival and reproduction of organisms. Adaptation examples are camouflage and mimicry.
Similarities between species
The similarities between different groups of living beings reinforces the idea that they may have a common ancestor during their evolutionary history. Some evidences are:
They are those with the same embryonic origin and anatomical similarities, but with different functions. The process that originated the homologous organs is called evolutionary divergence. An example is the upper limbs of a large part of vertebrates.
They are those of embryonic origin and different anatomical structures but that have the same function. Analogous organs arise by evolutionary convergence. An example is the wings of birds and insects.
They are atrophied organs and without apparent function. An example is the human appendix, which represents a vestige of a compartment of the intestine that harbored microbes for the digestion of cellulose in our herbivorous ancestors.
When the embryonic development of some species is observed, it is noted that they are very similar in some aspects. This shows evidence of common ancestry. For example, fish, amphibians, reptiles, birds and mammals are very different when adults, but their embryos are very similar
Advances in molecular biology have allowed us to compare the genetic structure of different species. These studies are complemented by anatomical and embryonic similarities and confirm the kinship relationship between the species.
Mechanisms of biological evolution
The theory of neo-Darwinism considers the following mechanisms as factors that contribute to the evolutionary changes:
A mutation corresponds to any alteration in the genetic material of an organism that can originate a new characteristic. If this new feature offers some advantage to the individual, the allele (the mutation) tends to be preserved by natural selection.
For example, sickle cell disease is a disease caused by a mutation in hemoglobin, the protein that carries oxygen in the red blood cells of humans. This mutation prevailed in Africa because abnormal red blood cells resist infection by the malaria parasite, with higher prevalence in these countries.
The genetic drift corresponds to a process of random alteration of the allelic frequencies of a population. For example, in a population of ten ducks, eight are brown and two are white. When they flew, hunters targeted and killed the two white ducks, leaving only the brown ducks to reproduce each other.
Genetic drift has no predilection for a particular characteristic or adaptation, that is, it does not depend on the beneficial or harmful effects of an allele. The effect of genetic drift is more pronounced in small populations.
Natural selection is one of the fundamental mechanisms of evolution. Through it, the individuals most adapted to a certain condition are selected . Thus, they are more likely to survive, reproduce and transmit their characteristics to their descendants.
Natural selection can only take place if there are differences in a population. These differences must have a genetic basis, otherwise, the selection is not transferred to the next generation.
This aspect is fundamental, since there are differences between individuals that can be caused by non-genetic reasons. For example, for an individual to be taller due to better nutrition instead of having a different gene.
Although the theory of evolution generated controversy when it was first proposed, it is now widely accepted in the scientific community. However, the theory of evolution is a difficult concept and misconceptions have been generated around it.
“Evolution is only a theory”
Critics to the theory of evolution discredit its importance by saying that it is a theory, in the vulgar sense of the word. In science, a theory is a body of widely tested and verified explanations for a set of observations of nature.
Evolution is the change in the genetic composition of a population over time, not the individual change during its life cycle.
“Evolution explains the origin of life”
The theory of evolution explains how populations change over time, does not explain how life originated in the universe.
“The organisms evolve with a purpose”
The fact that “organisms evolve in response to a change in their environment” can lead to the misconception that evolution is somehow intentional.
“Evolution is equal to natural selection”
The terms “evolution” and “natural selection” are sometimes used as synonyms, but they are not. Natural selection refers to the process by which organisms better adapted to their environment are more likely to survive and produce offspring, favoring a certain genetic trait in the population. Evolution is a broader term and refers to any change in the genetics of a population over time.