BeyondET
Well-Known Member
That just isn't accurate. Almond shaped eyes aren't limited to Asians. One of my favorite actors, Keanu Reeves, has almond shaped eyes. He may have some Asian ancestors, but that's the point. Our physical traits aren't determined by a single gene, though a single gene can have a profound effect on any given recognizable trait.
A "breeding population" (some geographic area that is isolated from other areas by barriers to easy population mixing) has a broad mix of genetic material for any given trait (called a gene pool), but some environmental conditions may favor certain traits over others. That is, some traits may be more attractive to the opposite sex, some traits may help survive diseases, or favor an individual in hunting, gathering, warfare, etc.
These favorable traits will become , over generations, more dominant in that population, but since human beings have two genes for each function, with either one dominant over the other, or one partially dominant, the processes of miosis to produce gametes (reproductive cells with only 1 set of genes, half the normal genome) causes 4 possible genetic combinations in any fertilized egg for any given genetic traits.
A dominant gene can be expressed in 3 out of 4 combinations, but the subdominant (recessive) gene can be carried in 3 out of 4 combinations and will persist in a population, even if it leads to early morbidity and death in 1 of the 4 combinations. The gene pool retains the recessive trait, even if it isn't expressed.
There are about 20,500 genes in the human genome, each gene representing 4 possible gene combinations, and each trait expressed by 4 "genotypes" times the number of genes responsible for any given trait. That's a lot of potential variation in the gene pool of any given population.
Now the expression of the dominant and partially dominant genes is called phenotypic expression. Phenotypic expression is responsible for "breeds" or "races", the appearance of isolated groups in any given species, but the recessive genes persist in the population in healthy quantities (as much as three quarters of the population).
There are also environmental factors that effect the phenotypic or morphological expression of genes. Some genes (if not all) are "turned" on or off by environmental factors. Neither growth or maturation would be possible if this weren't true.
This gives us much greater variation in the morphological expression of any genotype. Eg. A baby looks different from an adolescent or adult, not just a smaller version of the same. Nutrition and exposure to biologically active substances in the environment alter phenotypic expression.
All this is to say that you never see all the genetic traits in a population, yet they persist. For example, a Caucasian may have (and does have) some of the genes that produce black skin coloration, but not the full set required to produce that phenotypic expression. In other words, Caucasian parents are capable of producing children with traits common in other races, but as a rare occasion when multiple genes are required to produce a given trait.
When "intermarriages" occur between "races", the children express phenotypes closer to the original model. The genetic combinations between the parents restore the genetic diversity suppressed by geographic isolation in a given breeding population.
This has been going on since the creation of man. We are all direct descendants of Adam as well as of Noah, and of their respective wives.
Stem cell programming have alot to do with things turning off and on as well. A caterpillar to butterfly is a good example of stem cells turning off and on at a predetermined interval.