How dose natural selection produce adaptations in a species?

For natural selection to occur, several premises must be satisfied. Firstly, there must be variation in a population. If all individuals are the same, there is no variation on which selection can occur. Secondly, these traits must be heritable, meaning they are passed from parent to offspring. Natural selection cannot operate on traits that have no genetic basis. There must also be differential reproduction, which means that some individuals must reproduce more than others. When all of these factors occur, natural selection results in evolution as advantageous traits propagate throughout the population.

Natural selection is quite variable, as changes in the environment impact what traits are advantageous in a particular time and place. A good of example of this comes from Galapagos finches. These birds have varying beak sizes. Wide beaks are best for eating hard seeds, while long narrow beaks are more adept at exploiting the fleshy fruit from trees. Typically narrow beaks are more prevalent, but during drought conditions when trees cannot produce fruit, seeds become a more abundant food item. This results in those finches with wide beaks having more food available and reproducing more than those with narrow beaks. When droughts persist over many years, wide beaks replace narrow beaks as the most common, but this trend reverses when droughts end and fruits once again become available.

When there is a natural selection upon any species this means that that specific species has an adaptation / a increase in survival skills .

There a Giraffes for EXAMPLE : one group of giraffes have medium length necks and the 2nd group has longer necks , so they can reach the 85 foot tall trees.

That was an example of natural selection , i hoped that my answer helped yo out a lot , have a nice day. 

 

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.