Evolution Theory

Fossils, Lamarckism, Darwinism Explained in Q&As

Origin of life diversity

1. What is the problem that the theory of evolution and its rival theories try to solve?

The problem that the theory of evolution, or simply evolution, and its rival theories try to solve is to explain how the different living beings that live on earth have appeared.

Evolution Theory - Biology Questions and Answers


2. What is the main theory opposed to evolution?

The main theory that opposes the evolution theory on the explanation of how species emerged (phylogenesis) is fixism.

3. What is fixism?

Fixism is the theory about the diversity of life on earth that affirms that the current existent species were identical to species of the past and came out already adapted to the environment without undergoing changes.

Fixism opposes evolutionism since evolutionism is the idea that current species emerged from gradual transformations suffered by ancestral and extinct species.

The religious version of fixism is called creationism. Many different forms of creationism are found in the mythology of various religions. Modernized religious interpreters teach creationism as a metaphorical wisdom and not as opposed to evolutionism.

Furthermore it is possible to make evolution compatible with creationism by considering that God in His perfection would not create a world so full of imperfections and sufferings like our world. One can maintain the creationist belief thinking that the world God created is another much better world or at least not the one that we see while admitting the imperfection of life that we see has emerged by evolution.

4. In the scientific competition against fixism what are the main arguments that favor evolutionism?

The main arguments in favor of evolutionism are: paleontological, from the study of similarities among fossils of different periods; of compared anatomy, the existence of structures with same origin and function and of residual organs, like the human appendix, that reveal relationships among species; of compared embryology, similarities of structures and developmental processes among embryos of related species; of molecular biology, larger percentage of similar nucleotide sequences in the DNA of species having common ancestors.

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5. What are fossils?

Fossils are petrified vestiges of beings that lived in the past conserved by chemical and geological processes and found within rocks and sedimentary strata of the terrestrial crust. 

  • Evolution Theory Review - Image Diversity: fossils

6. How does the study of fossils strengthen the theory of evolution?

The study of fossils reveals ancient and extinct species having many similar structures to others of the present and of the past. Fossils still allow radioactive dating to estimate the periods during which species lived and to establish a chronological relationship between them. Those evidences strengthen the hypothesis of relationship and common origin among species and that their features have modified gradually until the formation of the current species.


7. Historically what were the two main evolutionary theories?

The two main evolutionary theories were lamarckism and darwinism. 

8. What is meant by the law of use and disuse and by the law of the transmission of acquired characteristics?

According to the law of use and disuse the characteristics of a body vary as it is more or less used. This rule is valid for example for features like the muscular mass and the size of the bones.

The law of the transmission of acquired characteristics in its turn established that parents could transmit to their offspring characteristics acquired by the law of use and disuse.

9. What is lamarckism?

Lamarckism is the theory that unites the law of use and disuse with the law of the transmission of acquired characteristics, i.e., that asserted that acquired characteristics, for example, the muscular mass, could be transmitted from a parent to its offspring.

The theory was proposed by the French naturalist Lamarck in the beginning of the 19th century. At that time the idea was not so absurd since nobody knew how the transmission of hereditary characteristics occurred. (Lamarck had great merit in introducing an evolutionary theory based in natural law at a time dominated by fixism.)


10. Who was Charles Darwin?

Charles Darwin was an English naturalist born in 1809 and considered the father of the theory of evolution. At the end of the year 1831, before turning 23 years of age, Darwin embarked as volunteer scientist on the ship the Beagle for a five year expedition to the South American coast and the Pacific. During the voyage, whose most famous passage was the stop in the Galapagos Islands, Darwin collected data that he used to write his masterpiece “The Origin of Species” (1859). In this book the principles of the common ancestry of all living beings and of natural selection as the force that drives the diversity of species were described. Darwin died in 1882.

(The original name of the most famous book written by Darwin was “On the Origin of Species by Means of Natural Selection”.)

11. What is the mechanism described by Darwin that eliminates species less adapted to environmental conditions?

The mentioned mechanism is the natural selection.

12. How did Darwin reach the principle of natural selection from the observation of differences among individuals of the same species?

Darwin recognized that in a same species there were individuals with different characteristics. He also realized that those differences could lead to different survival and reproduction chances for each individual. Therefore he discovered the importance of the environment acting upon organisms and preserving those having more advantageous characteristics for survival and more able to generate offspring and so he described the basis of the principle of natural selection.

13. How did the industrial revolution in England offer an example of natural selection?

One of the classic examples of natural selection is regarding the moths of industrial zones of England in the end of the 19th century and the beginning of the 20th century. As the industrial revolution advanced the bark of the trees that moths landed on became darker due to the soot released from factories. The population of light moths then decreased and was substituted by a population of dark moths since the mimicry of the dark moths in the new environment protected them from predators, i.e., they had an adaptive advantage in that new environment. Light moths in their turn suffered the negative effect of natural selection for becoming more visible to predators and were almost eliminated. In the open forest far from factories however it was experimentally verified that light moths maintained their adaptive advantage and the dark moths continued to be more easily found by predators.

  • Evolution Theory Review - Image Diversity: moths

14. What are the fundamental similarities and differences between lamarckism and darwinism?

Both lamarckism and darwinism are evolutionary theories as opposed to fixism, both admit the existence of processes that caused changes in the characteristics of the living beings in the past.

They have however different explanations for those changes. Lamarckism combines the law of use and disuse with the law of the transmission of acquired characteristics to explain the changes. Darwinism defends the action of the natural selection. 

The synthetic theory of evolution

15. In the time of Darwin the results of Mendel’s research on biological inheritance had not been published, Genetics was not yet developed, neither DNA nor the concept of genetic mutation were known. What is the modern darwinist theory that incorporates these bodies of knowledge?

The modern darwinist theory that incorporates knowledge from Genetics and Molecular Biology is called neodarwinism, or synthetic theory of evolution.

16. How does the synthetic theory of evolution incorporate knowledge from Genetics and Molecular Biology into the darwinism?

Today it is known that variation of inherited characteristics is created by alterations in the genetic material of the individuals, more precisely by modifications or recombinations of DNA molecules. Small changes in the genetic material accumulate and new phenotypical characteristics emerge. The carriers of these characteristics then are submitted to natural selection. From modern Biology its recognized that natural selection generates in a given population an increase in the frequency of alleles and genes more favorable to survival and reproduction; less advantageous genes and alleles tend to be eliminated.

17. Using the concepts of variability, environmental pressure and natural selection how does the synthetic theory explain the darwinian natural selection?

Genetic variability occurs from recombination of chromosomes during sexual reproduction and from DNA mutations in germ cells and gametes. Such variability creates individuals who are carriers of some new phenotypical characteristics compared to their ancestors. These individuals are submitted to environmental pressure and can be more or less well-succeeded concerning survival or reproduction. Those better succeeded transmit their genetic patrimony to a larger number of descendants increasing the frequency of their genes in the population; those less well-succeeded tend to transmit their genes to a small number of descendants decreasing the frequency of their genes in the population or even becoming extinct. This process is called natural selection (preservation of organisms that present more adapted phenotypes for the environmental pressure they face).

18. In hospitals where many tuberculosis patients are treated the population of the tuberculosis mycobacteria may be constituted of multiresistant (to antibiotics) strains. How does the synthetic theory of evolution explain this fact?

The appearance of multiresistant strains of pathogenic parasites in hospitals, for example, of multiresistant tuberculosis bacteria, can be explained by the synthetic theory of evolution.

As in any environment, TB bacteria in hospitals undergo changes in their genetic material. In the hospital environment however they suffer continuous exposition to antibiotics. Many of them die by the antibiotic action but carriers of mutations that provide resistance to those antibiotics proliferate freely. These resistant microorganisms when submitted to other antibiotics again undergo natural selection and those which became resistant to these other drugs are preserved and proliferate. Thus strains of multiresistant (nontreatable) mutant bacteria emerge in hospitals.

The use of antibiotics is a factor that promotes natural selection and the emergence of multiresistant bacteria. This is the reason why hospitals often have committees that control the use of antibiotics.


19. What is reproductive isolation?

Living beings are considered under reproductive isolation when they cannot cross among themselves or if they can cross but cannot generate fertile offspring.

20. What is the relationship between the concept of reproductive isolation and the concept of species?

Reproductive isolation is an important concept because it defines the concept of species: only living beings that can cross among themselves and generate fertile offspring, i.e., that are not under reproductive isolation, belong to the same species. For example, humans and chimps are under reproductive isolation and are not of the same species.

21. What is speciation?

Speciation is the process by which different species emerge from a common ancestor species. Speciation generally begins when populations of the same species become geographically isolated, i.e., when they are separated by some physical barrier that disallows crossing between individuals from one population and individuals of another population.

Groups that for a long time are kept under geographical isolation tend to accumulate different phenotypical characteristics from each other by means of genetic variability (mutations and recombination) and natural selection. When those differences reach a point that makes the crossing of individuals of one group with individuals of the other group impossible or the generation of fertile offspring no longer happens it is said that speciation has occurred.

  • Evolution Theory Review - Image Diversity: speciation

22. Why does geographical isolation lead to speciation?

Geographical isolation between groups of the same species leads to formation of a new species since it disallows crossing among isolated individuals. Distinct characteristics from the other groups are incorporated by genetic variability and natural selection into the isolated groups until the emergence of a new species. So the geographical isolation creates the reproductive isolation.

Adaptive convergence and adaptive radiation

23. How can the fact that fishes and dolphins have similar organs and similar general shape be explained?

Fishes and dolphins have similar organs and shape because although they have phylogenetically distant ancestors they face similar environmental pressures since they share the same habitat (water). So by undergoing genetic variability and natural selection some similar features, for example, the hydrodynamic body and the presence of fins, were incorporated into these animals.

24. What is adaptive convergence?

Adaptive convergence is the phenomenon by which living beings facing the same environmental pressure (problems) and undergoing genetic variability and natural selection incorporate similar (analogous) organs and structures (solutions) into their bodies during evolution. For example, the fins and the hydrodynamic body of fishes and dolphins, phylogenetically distant animals. 

25. What is adaptive radiation?

Adaptive radiation is the appearance of several other species from one common ancestral species that have spread to various regions or environments. The different characteristics among the species correspond to the adaptive necessities of the ecological niches each one occupies, i.e., to different environmental pressures.

Analogous and homologous organs

26. What is the difference between analogous and homologous organs?

Characteristics of different species are said to be analogous when having the same biological function, for example, the wings of bats and the wings of insects.

Characteristics of different species are said to be homologous when having the same biological origin, i.e., when they are products of differentiation of a same characteristic from a common ancestor, like cat paws and human feet. (Characteristics of different species may be analogous and homologous.)

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