Asked about the statement:
navneet9431 said:
Variation during reproduction is beneficial to the species but not necessarily for the individual?
This is a statement about genetic inheritance of factors affecting reproductive success in a breeding (evolutionarially successful) population. These would be the genetic factors, in a breeding population, selected for (at some time when genetic variation is needed), due to their position in some gradient of the genetic variation.
What you just described:
navneet9431 said:
I think it is beneficial for species because it helps the species of various organisms to survive and flourish even in adverse environment. For example if there is a population of certain bacteria living in temperate water (which is neither very hot no very cold) and the temperature of water increases too much due to global warming then most of these bacteria will not be able to tolerate excessive heat and hence die but some bacteria which had variations to resist heat would survive and grow further.
is a good example of the beneficial side of the statement:
navneet9431 said:
Variation during reproduction is beneficial to the species
The
navneet9431 said:
not necessarily for the individual
part is just saying that, at some some times when variation in reproductive success, at a population level can be good for survival (and being positively selected for) will not work out for all sections of a reproductive population.
At some point, there will be winners and losers, perhaps resulting from a change in environment, as you suggested.
Some of those organisms, will not reproduce or may out right die (equivalent from an evolutionary point of view, not adding genetically, to the next generation).
From the point of view of an individual (in the genetically based losing part of the population), the effects of the changes (which population level genetic variation can overcome) will not be beneficial to all individuals with in the population. Some will be in the reproductively losing part of the population. They are the "not necessarily (beneficial) for the individual" part.