Species and speciation

• Linnaeus et al. grouped organisms based on morphology (clearly distinguishable shapes and forms)
• "Biological species concept" by Ernst Mayr in 1942 is the predominant definition now
• A species is a group of an interbreeding population which is reproductively isolated from other such groups
• To be reproductively isolated is to be unable to interbreed with other species
• If two parents create an offspring that is infertile, the parents were not of the same species
• If two parents create an offspring that is fertile, the parents are of the same species
• A hybrid is an offspring that results from sexual reproduction between 2 closely related but separate species- they often don't have scientific names
• An example of a hybrid is a mule that was artificially created to be more compact than horses but stronger and smarter than donkeys
• Species aren't clearly defined as they can differ gradually across a geographical region and they are not discrete but merely an approximation
• Determining independent/divergent species can be difficult due to logistics and technological limitations or ethical considerations for interfering with nature
• Typical manners of determining distinct species cannot be applied to extinct ones as they cannot be made to reproduce
• Due to difficulties in determining distinct species in other ways, the most common way of identifying species is by comparing morphological characteristics such as size, shape, colour etc.
• Chronospecies are different stages in the same evolving lineage that existed at different points in time without splitting or branching. Here, splitting species based on the Biological species concept is stupid as its unclear where one species begins and where the other ends
• The biological species concept is only applicable to sexually reproducing organisms
• Asexually reproducing organisms are often sorted by appearances or biochemical similarities
• Apomixis is the process of asexual reproduction in which seedlings are germinated as genetically identical clones of the parent plant but since no interbreeding occurs, they would be considered isolated under BSC
• Genome sequencing has revealed that separation between species in not always complete and genes are sometimes transferred from one species to another using horizontal gene transfer
• Horizontal gene transfer means populations are not always genetically isolated from each other and cannot be defined using BSC
• Cladograms depict hypothesized evolutionary relationships between organisms
• Speciation is the process by which a population of species diverges into two distinct species
• Divergent evolution results in immense diversity of life on Earth but due to shared ancestors, life forms continue to share some structures and processes
• The alternations of a single species over time eventually produces a population physically, morphologically, and/or genetically distinct from their ancestors
• Throughout change, however, there is still only a single evolutionary species which is the result of directional selection
• The rate of extinction is never constant but it is estimated to have happened at least 5 times in the last 500 million years and wiped out 75-90% of existing species, making way for new life forms
• Genetically diverging populations may be hard to distinguish as unique species as the speciation process is occurring because there is a continuum from merely somewhat restricted gene flow within the ancestral species and the complete reproductive isolation of resulting species
• Speciation's first step is reproductive isolation where populations stop interbreeding due to barriers that prevent gene flow between the gene pools of two populations of the same species.
• The Apes lived in the rainforests of Congo where sedimentary analysis revealed that the water level dipped for a while, allowing the ancestor of Chimpanzees to cross over to the north side of the river. As a flood increased the water level again and prevented their crossing back over, the first step of speciation (productive isolation) was accomplished
• The second step of speciation is differential selection that results from post-separation selection pressures like more or less competition for food, different climates or predators, and different food sources. Natural selection responding to these changes cause populations to grow more and more distinct, not able to interbreed with the other variation of the ancestors. This causes them to be separate species according to BSC
• Differential selection in the specification of Apes occurred when the two populations were separated and the Chimpanzees had to compete with gorillas for food and territory while the Bonobos did not. Chimpanzees now have large heads and muscular bodies and are very aggressive while Bonobos are thinner with smaller heads and an inclination to teamwork and resolutions.
• A population is a group of the same species in the same place at the same time
• If a population doesn't interbreed, their distinct physical and behavioral differences will accumulate and separate them into distinct species
• "Grolar bears" are hybrids resulting from Grizzly bears' climate-change-induced move northwards. Due to Grizz and Polar bears coming from close ancestors, their reproductive isolation might be incomplete, creating hybrids upon regaining contact with the other population.
• A directional selection causes populations to evolve towards one end of a trait spectrum. Traits can be discrete and have specific variations (think eye color), other traits are continuous, and exists as a wide range of nearly infinite values (think height). If a discrete trait is directionally selected, only one variety will be selected for (only blue eyes). If a continuous trait is directionally selected, the highest or lowest value will be selected for (only tall people).
• Transduction: Bacterial DNA moves from one bacterium to another via a virus
• Conjugation: Transfer of DNA via plasmid from one to another during cell-to-cell contact
• Transformation: DNA is "up-took" from the environment. This is common in bacteria by not so much in eukaryotes
• Individuals with shorter lifespans reproduce more and see more evolution
• 2.5 billion years ago, atmospheric oxygen rises significantly because of oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere