Does "race" exist, and if so, how do you define it?

Excellent question for discussion, and a very loaded one too. Race is a political word and a social construct.

Humans in general need to classify things in order to try to understand the world around them. Race, in its most innocent use of the word, is simply a way to categorize people who look different from oneself or have very different cultures.

The flip side is the political use, which is generally only called upon to draw attention to those differences. It immediately creates an "us against them" situation.

Let´s ask a raceless being from another dimension, because no one here on this earth is qualified to define it properly.

As an EP friend of mine says, I´d say we are all multinese.

Are you kidding me? Of course race exists or it wouldn't be a word in the english language! here's my definition:
n.

1. A local geographic or global human population distinguished as a more or less distinct group by genetically transmitted physical characteristics.
2. A group of people united or classified together on the basis of common history, nationality, or geographic distribution: the German race.
3. A genealogical line; a lineage.
4. Humans considered as a group.
5. Biology.
1. An interbreeding, usually geographically isolated population of organisms differing from other populations of the same species in the frequency of hereditary traits. A race that has been given formal taxonomic recognition is known as a subspecies.
2. A breed or strain, as of domestic animals.
6. A distinguishing or characteristic quality, such as the flavor of a wine.

[French, from Old French, from Old Italian razza, race, lineage.]

USAGE NOTE The notion of race is nearly as problematic from a scientific point of view as it is from a social one. European physical anthropologists of the 17th and 18th centuries proposed various systems of racial classifications based on such observable characteristics as skin color, hair type, body proportions, and skull measurements, essentially codifying the perceived differences among broad geographic populations of humans. The traditional terms for these populations—Caucasoid (or Caucasian), Mongoloid, Negroid, and in some systems Australoid—are now controversial in both technical and nontechnical usage, and in some cases they may well be considered offensive. (Caucasian does retain a certain currency in American English, but it is used almost exclusively to mean “white” or “European” rather than “belonging to the Caucasian race,” a group that includes a variety of peoples generally categorized as nonwhite.) The biological aspect of race is described today not in observable physical features but rather in such genetic characteristics as blood groups and metabolic processes, and the groupings indicated by these factors seldom coincide very neatly with those put forward by earlier physical anthropologists. Citing this and other points—such as the fact that a person who is considered black in one society might be nonblack in another—many cultural anthropologists now consider race to be more a social or mental construct than an objective biological fact.

Race is the human race. Ethnic groups is what separate the different cultures.

All traits are noticable in the various human race

were u are born....

Actually the scientific term is genetic variation.