Tag: origin of life and organic evolution

• Reproductive isolation refers to a set of mechanisms that prevent animals of the same group from breeding. These are reproductive barriers that do not allow the species to mate and produce offspring.
  
• Mule is an example of low hybrid viability type of reproductive isolation.
  
• Even though horses and donkeys can mate and produce healthy offspring, the offsprings thus produced termed mules cannot pass their genetic information down to future generations, so they are a genetic dead-end. There is no gene flow through infertile hybrids.
  

• Ecological isolation is a type of reproductive isolation in which mating is prevented because of the separation of species resulting from the difference in their habitat. 
  
• This usually occurs when the species are used to different habitat types, or different parts of the same habitat. Even if the geographic range of two species overlaps, the difference in their ecological needs and breeding requirements is enough to isolate them from each other.

• Reductions in population size and absence of gene flow can lead to reductions in genetic variability, reproductive fitness, and a limited ability to adapt to environmental change increasing the risk of extinction. 
  
• Island populations are typically small and isolated, and as a result, inbreeding and reduced genetic diversity elevate their extinction risk.
  

• The principle of Malthusian theory of human population states that human populations grow exponentially (i.e., doubling with each cycle) while food production grows at an arithmetic rate (i.e. by the repeated addition of a uniform increment in each uniform interval of time). 
  
• This scenario of arithmetic food growth with simultaneous geometric human population growth predicted a future when humans would have no resources to survive on. To avoid such a catastrophe, Malthus urged controls on population growth.
  

Miller circulated four gases - methane, ammonia, hydrogen and water vapour in an air tight apparatus and passed electrical discharges from electrodes. He found a large number of simple organic compounds including some aminoacids such as alanine, glycine and aspartic acid.