Darwin and Lamarck’s Evolutionary Theories Compared: What Each One’s Theory of Evolution Says and What Speciation Is
Theory of evolution
By evolution we mean the change in the genetic heritage of members of a population over time. When changes in the genetic heritage take shape in a short time we speak of microevolution , when longer times are required we speak of macroevolution .
As for species, the naturalist Carl Linnaeus placed animals, plants and minerals in a hierarchical system divided into kingdoms, classes, orders, genera and species. Each species, according to the naturalist, remained unchanged over time. But when many fossils were found in the eighteenth century, it was understood that there must have been an underlying complexity that grew over time. Scientists explained this process in different ways.
Lamarck’s theory
According to Lamarck, the complexity of fossils was due to the interaction of living species with the environments and with changes in diet; the well-known example is that of giraffes, which would have developed a long neck due to the continuous use of the organ.
Darwin’s theory
Darwin understood that species evolve over time from simple to composite forms. Artificial selection carried out by man serves to advance only those qualities favorable to a given purpose. According to Darwin , in the struggle for survival, the strongest individuals did not win, but those most suited to a particular place and period. The main agents of evolution depend on differential survival and different reproductive capacity.
The adaptation
Adaptation consists in the development of characteristics suitable for survival in an environment, whether it is physical, i.e. the habitat, or as a whole, such as food and a partner. But evolution does not always bring about new changes: for example, some penguins seem to go backwards instead of forwards.
The phenomenon of convergence says that some animals that derive from different and independent evolutionary lines seem to converge towards solutions that are very similar to each other.
The principles of Darwin’s theory of evolution
The principles of Darwin’s theory of evolution are:
- There are differences between individuals of the same species;
- These differences are related to the reproductive success of the individual and its reproductive rate and the average number of offspring;
- These differences are inevitable in order to be passed on to children;
- The struggle for existence is a device that allows us to foresee which individual will leave more descendants.
Evidence of Evolution
The evidence for evolution is:
- Fossils from the simplest to the most complex;
- The geographical distribution of living things;
- Studies in comparative anatomy;
- Comparative embryology studies show remarkable similarities between embryos of related organisms so much so that ontogeny summarizes phylogeny and many embryos start from the same form to differentiate over time;
- Common molecular biology tests.
The mechanisms of evolution
Evolution is the variation of allele frequencies in a population . Let’s take an example: if all individuals of the same species had the same genetic makeup, no evolution would be possible. In fact, if there were only individuals who were all the same, natural or artificial selection would have no possibility of choosing.
The term population refers to groups of organisms belonging to the same species and occupying a specific geographical area. The gene pool of a population is the set of all the alleles of all the genes of all the individuals that make up a population, the frequency of the alleles that make up the gene pool of a population is the basis on which evolution works.
Each individual in the population presents a diversity (this phenomenon is called polymorphism) whose source is genetic variability, and at the origin of variability there are mutations and rearrangements of characteristics. Genetic variability can be linked, in some cases, to the relationship with the environment in which the organism develops.
Evolution is not perfect
Evolution is not perfect :
- there are limits to what each organism can do;
- the selection does not create anything, but only chooses the most suitable variant;
- organisms “chosen” by evolution can be eliminated by catastrophes;
- adaptations often represent compromises;
- living beings have a history, they derive from remodeled ancestral structures;
- the genetic variation necessary to perfect a characteristic may never occur;
- some solutions adopted can condition, by limiting it, the subsequent evolution .
What is Speciation?
Speciation is the evolutionary process that allows the formation of new species. In most crosses no individual is formed, and if it is formed it is hybrid but not fertile. This contributes to reproductive isolation.
Reproductive isolation is ensured by:
- to a temporal isolation (mating period),
- to an ethological isolation (poor attraction),
- to mechanical isolation (incompatibility of genital organs),
- to genetic isolation (the gametes do not recognize each other),
- to gametic isolation (the gametes do not survive in each other’s pathways).
Speciation occurs when, in addition to mutations and natural selection, various other factors intervene that isolate the original population into distinct populations. The process occurs in two phases:
