If different species have different number of Chromosomes......?

Question

When a new species evolve, it would be different from its parent.

In the case of higher class of animals with sexual distinction of male and female, can a newly evolved individual mate with its ancestral individual to reproduce a healthy (non-hybrid) species of the new kind?

Then how can it be said that evolution is gradual? Once a new species with a different number of chromosome character come into existence, it has to find a mate with its own type to sustain that particular species.

How can it be like a community speaking Greek gradually changing to Latin speaking community?

Some experts please explain the scenario how the new species of man came into existence?

Answer 1

The number of chromosomes can change in two ways ... by splitting of a chromosome, or fusion of two chromosomes into one.

In either case, what is important is not the number of chromosomes, but whether the genes are contained on them.

For example, wild horses have 66 chromosomes, while domestic horses have 64.   But the wild horses can not only mate with domestic horses, but the resulting offspring are themselves fertile and can continue mating.  So individuals with different numbers of chromosomes clearly CAN mate and continue the species.

So it is NOT true that a new individual with a different number of chromosomes must find a mate with the same number of chromosomes.  Again, it is not the number of chromosomes that matters, but the genes on those chromosomes.

>"How can it be like a community speaking Greek gradually changing to Latin speaking community? "

Well ... Greek is not ancestral to Latin so that's not a good analogy.   However, Latin is ancestral to Italian.  So in the same way that the language spoken in downtown Rome can change slowly from Latin to Italian over the centuries, without any child ever speaking a "different language" from his parents ... a population of mating individuals can go slowly from one set of characteristics to another without any offspring ever being a "different species" than its parents.  

This can include a change in the number of chromosomes ... this doesn't occur in a single generation ... but once a new chromosome count does appear, if it has any advantage, then the old chromosome count will get displaced in a small number of generations (a few hundred) especially if it is a small population.   This is why we don't find many species (like horses) that are in the middle of the transition.

The reason humans have 23 pairs of chromosomes, while other ape species have 24 pairs, can be traced to the fusion of two chromosomes.  Human chromosome #2 has letter-for-letter sequences of DNA found on two separate chromosomes on the other apes ... right down to what's called the telomeres ... DNA that terminate the tips of chromosomes, but found fused in the middle of our Chromosome #2.