Gaps or Borders between Species
There is obviously a big gap between all ape like so called humanoid fossil skulls with brain sizes of about a pint and those human skulls with brain sizes of two or even three pints.
The human brain itself grows very quickly in the first three years after birth, reaches its maximum by adolescence and then keeps slightly shrinking until death.
Variaton of Species
All species can diversify into many different races by natural or human selection and combination of their parents.
Mutations often bring unwanted abnormal variations of size or ?
Many of these mutations if not all of them make its beings sick, weak or lessabled instead of improving the living of their being.
Cross Breeds or Hybrids
are possible but only by losing their fertility, so that they cannot have own children. Every generation has to be breeded again!
can only be brought by other living beings. Many scholars are trying to design their own viruses, bacterias and cells and they are able to change many genes but i hope that they never will be too successfull playing divine creators.