The Possibility of Species Merger Through Natural Selection and Evolution: Insights and Examples
Understanding the process of natural selection and evolution within the framework of species formation is a fascinating topic in the field of biology. While the concept of two different species merging to form a new one is often discussed, the reality is more nuanced. Let us explore this intricate process through the lens of scientific evidence and examples, focusing on the concept of allopolyploidy and the formation of new species in the plant kingdom.
Interfertility by Definition
Species are defined as groups of organisms capable of interbreeding and producing fertile offspring. However, this does not apply to the formation of entirely new species from distinct parental species. In general, different species are not interfertile due to reproductive barriers like distinct chromosomal structures, which create offspring that are often sterile. This definition is strict, and mechanisms that allow for the creation of new species, such as allopolyploidy, fall outside the conventional boundaries.
Neandertal and Modern Human Merger
A notable example of interspecies genetic mingling is through the admixture of Neandertals and modern humans. This occurred as early humans migrated out of Africa and encountered Neandertals in Eurasia. Genetic studies have confirmed this through the presence of Neandertal DNA in the genomes of non-African people. According to K Lohse and LAF Frantz (2014), Neandertal admixture has been confirmed by maximum-likelihood analysis of three genomes, published in the journal Genetics (volume 196, pages 1241-51, doi: 10.1534/genetics.114.162396).
The significance of this merger is evident in the physiological differences between Neandertals and modern humans. Neandertals exhibited features such as pachyosteosclerosis (thickened bones), huge brain size, ear exostoses, large nose, platycephaly (low, broad skull), and large lungs, which are not present in modern humans. These differences underscore the genetic and evolutionary distinctiveness of the two groups.
Merger Through Allopolyploidy
While genetic merging between distinct species is rare, the concept of species merger through natural selection and evolution can occur through allopolyploidy, a process where two different species merge to form a new one. A classic example of this is the cotton plant, Gossypium hirsutum, which is an allotetraploid derived from the hybridization of two different Gossypium species. The closest living relatives of the parent species are most likely the diploid species G. arboreum and G. raimondii.
The process of allopolyploidy allows for the creation of a new, fertile species. This occurs because the hybrid plant's cells now carry two sets of chromosomes from both ancestral species, with each chromosome pair having a homologous partner. When these gametes (sperm and egg cells) are produced, the resulting offspring can be fertile. This restoration of fertility leads to the establishment of a new, robust species.
Triploid Offspring
While most triploid offspring are sterile due to the mismatched number of chromosomes (received from one tetraploid and one diploid parent), some evolutionary advantages can arise from this condition. Triploid varieties of bananas, watermelons, and grapes are examples of such evolution. These seedless varieties are triploids, which have three sets of chromosomes, and their sterility leads to asexual reproduction.
However, polyploidy can also have evolutionary consequences. For example, Arachis hypogea (peanut) is thought to be the product of hybridization between A. duranensis and A. ipanensis. This process creates a tetraploid plant species, which is typically more robust than its diploid ancestors.
Conclusion
The process of creating new species through natural selection and evolution can be complex and multifaceted. While traditional definitions of species prevent the immediate merging of distinct species, mechanisms like allopolyploidy demonstrate the potential for new species to arise through the integration of genetic material from different parent species. This phenomenon, while rare, provides valuable insights into the dynamic nature of evolutionary processes.
Key Takeaways:
Interfertility is a strict definition of species distinction. Neandertal and modern human genetic mixing is a notable example of species genetic merging. Allopolyploidy allows for the creation of new, fertile species through the merging of different parental species. Triploid offspring can have evolutionary advantages, such as seedlessness in bananas, watermelons, and grapes.