Humans and many other organism

It has to be understood that whether haploid or diploideukaryotes exist in an ever-changing environment. Also, there ismicroevolution taking place in their genome, largely driven by themutations. We do understand that mutations are the reason for thevariance.

These mutations are also related directly to the ploidy of anorganism. Henceforth a diploid organism has more targets availablefor the mutations. Also, mutations are either beneficial or harmfuland thus determine the fitness of an organism. For a diploidorganism since there are two copies of the chromosomes present inthem, there are more than one targets available for the mutation toacquire and thus they can better mask a harmful mutation (as theywill be a mutation free copy of the gene available tocompensate)Now imagine if a harmful mutation takes place due to theenvironment that complex organism is, if it is diploid it hasbetter chances of survival, and thus it is more fit. Henceforth,these complex eukaryotes are diploid. Since evolution always drivessurvival of the fittest, imagine a haploid organism with a harmfulmutation (with no compensatory copy of the gene that will harborthe mutation) and a diploid organism with the same harmful mutationbut with a compensatory copy of the gene. Which one will have moresurvival chances or I must say which one will be more fit tosurvive. Undoubtedly, it will be a diploid organism. So from anevolutionary perspective too, the diploid state favors theorganism. So in the nutshell the diploid state has followingadvantages a) Fitness advantages over haploids in terms of theexposure to the mutations b) Better adaptability for masking themutation as they have a compensatory copy of the gene and c) theycan better adapt to the toxic environments as compared to theirhaploid counterparts.

Now this does not mean that being in a haploid state hasdisadvantages, that state has its own perks and they are asfollows: a) a larger surface to volume ratio b) a minimalmutational load and c) certain adaptability advantages in a lownutrient environment setup. Since the haploid organisms are smallerin the size as compared to the diploid counterparts they are betterat absorbing nutrients from their microenvironment as their surfaceto volume ratio is higher and that explains point a) and c). Sincethey have a haploid genome they bear less load off the mutationswin to the less availability of the targets, remember the mutationsalways happen in the base pairs of the DNA that constitute agene.