Talk:Lineage (evolution)

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Pitty this misses out the aboriginal australians etc.

[edit] problem with single ancestor account

Everyone has two immediate lineages—from one’s mother and from one’s father. And one’s lineage multiplies with each receding generation.

http://www.anthrosource.net/doi/abs/10.1525/an.2006.47.2.7?journalCode=an But the text of this article says:

An evolutionary lineage (also called a clade) is composed of species, taxa, or individuals that are related by descent from a common ancestor.

The reader is going to miss the fact that for creatures that reproduce sexually the "common ancestor" of some clade or lineage has to be either a male or a female. That picture is a great abstraction. The chart in the section called 'The "lineage" definition of human races' makes it seem that there was a single "first ancestor" of all the American Indians, for instance.

Moreover, the picture that the first quoted passage suggests is an individual as a point at the bottom of an inverted triangle composed of all the contributors to the genetics of the individual. The picture the article conjures up is a single (mutant) ancestor at the top and all of the lines of descent that fan out from that progenitor. The second picture leaves out all of the mates of the ancestor and the ancestor's descendants (unless there is some inbreeding going on). It is an impoverished picture. (The first picture could be impoverished if it does not trace both the maternal and paternal lines of descent culminating in the individual at the bottom.)P0M 04:14, 8 June 2007 (UTC)

[edit] Removal of human lineages

I have removed the claim that human "races" are representative of evoutionary lineages for these reasons:

Many contemporary biological definitions of race conceptualize races as evolutionary lineages within the human species.

• This is unsupported, and as far as I can see is an incorrect assessment of current academic opinion. It is correct to state that species are considered evolutionary lineages due to the fact that species are reproductively isolated, they therefore derive from distinct founding events by distinct sub-populations from a "parental" population. The concept of lineage is dependent upon reproductive isolation, species should be, by definition, reproductively isolated (though this may or may not be the de facto case), therefore the founding population of a new species is that generation of organisms that ceases to interbreed with members of the former "parental" population. After this event the respective populations may, over time, become distinct species, given certain other considerations. It should be noted that the founding population, or "common ancestors" of the new species, are likely more to resemble the parental population than the subsequent differentiated population. Isolation is almost certainly not the only driver of speciation events, there probably needs to be some sort of selective environmental pressure that promotes the isolated population to become significantly different from its parental population, leading to greater specialisation in the derivative population and, coupled with the reproductive isolation, a greater divergence of biology. Other contributing factors may involve the "founder effect" and "genetic drift", both due to the founder population representing a small unrepresentative sampling of the parental population. It is also correct to claim that in biology race is synonymous with subspecies, but this should not be conflated with the social construction of "race", which is an entirely different beast. In biology it is more accurate to discuss subspecies and not use the culturally and socially loaded term "race", and most biologists avoid the term "race" due to these considerations. The point of this extended introduction is that some definitions of subspecies maintain that a subspecies is a differentiated form of a species that is somewhat reproductively isolated, and displays some environmental differentiation, but not sufficient of either to represent a fully differentiated speciation event nor a fully reproductively isolated population, though some reproductive isolation may be apparent. The upshot is that whereas it may be correct to claim, as the article did that "Many contemporary biological definitions of race conceptualize races as evolutionary lineages" (it would be more accurate to replace the word "Many" with "Some", see Wikipedia:Avoid weasel words, and the word "race" with "subspecies"), it is less accurate to suffix this sentence with "within the human species" without providing a specific source to support this contentious and unsupported claim. Alun 21:56, 10 August 2007 (UTC)

Genetic data can be used to infer population structure and assign individuals to groups that often correspond with their self-identified geographical ancestry.

• Maybe this is true, but how is it relevant to the concept of subspecific classification with regards to lineage? This refers to self identification, a social concept, ad not any defined concept of evolutionary lineage. Alun 21:56, 10 August 2007 (UTC)

A primary motivation for categorizing human genetic variation in this way comes from biomedical research.

• Sure, fair enough. But what is the evidence that this categorisation is relevant to the concept of evolutionary lineage? Drawing nice lines between so called human "races" ignores the fact that there has always been genetic exchange between geographically proximate human populations, it tends to imply a genetic isolation between human populations which are geographically proximate. Can the editor show, for example, that any study displays genetic isolation between "Ethiopians" and "Arabian Arabs" or between "Siberians" and "Alaskans"? Which studies ever claim such geographically proximate populations of humans have ever been reproductively isolated? Alun 21:56, 10 August 2007 (UTC)

In this context, human races represent different genetic backgrounds that may influence the association of diseases with their causes (genetic or environmental).

• Even if this is true (which I doubt), how is it relevant to the concept of lineage? Showing that geographically proximate populations of humans are more genetically similar to each other than they are to populations that are more geographically distant populations is not even de facto evidence of discrete evolutionary lineages. This observation is irrelevant to the article, see above reasoning.Alun 21:56, 10 August 2007 (UTC)

• The concept of racial lineage is very similar to the concept of familial lineages in genealogy. This has led some commentators to describe races as extended families.

The concept of familial lineage is patrilineal, we tend to take our father's family name in Europe and the USA, our familial lineage is patrilineal. When we take an extended view of family we often include people who are not biologically related to ourselves as part of our family. Our auntie may be a blood relative (our mother's or father's sister), but they may equally be unrelated to us, like the wife of father or mother's brother, this equally applies to uncles but obviously in converse. These people are not by necessity related to us by genetics, they are related to us by convention. Family connections, like those of "race" are socially constructed and do not necessarily pertain to biological relatedness. Alun 21:56, 10 August 2007 (UTC)

• And those relationship accords with geographical placement of a current human group

Someone explain this sentence to me. I don't know what i's supposed to mean? Alun 21:56, 10 August 2007 (UTC)

• A major objection to the view that contemporary humans can be categorized into lineages is the existence of individuals with ancestry from multiple lineages. To accommodate admixture, the definition of races is expanded beyond straightforward lineages to include the possibility of fractional lineage membership. This is often represented graphically as a triangle plot (see Figure 4). The fuzziness of racial lineages has led to the description of races as fuzzy sets (Sarich & Miele 2004).

This is dependent upon the previous removed contributions. The main fallacy is that there is any concept of "admixture", as if there is any concept of "purity" and "admixture", this makes little sense in terms of evolutionary lineage. All human populations are "admixed", but none are "evolutionary lineages" due to the fact that no anatomically modern human population has ever been described as discrete evolutionary linages, and if it had, it would almost certainly represent a discrete species. Alun 21:56, 10 August 2007 (UTC)

Statement: In the context of the above observation it appears that it is the arbitrary classification that humans wish to impart which is at fault regarding the concept of subspecies, rather than nature itself. The human drive to compartmentlise and classify tends to arbitrary boundaries that may not necessarily occur in nature. Templeton and some others provide a framework for defining subspecies, the conclusion of which is that for subspecies to be recognised they must achieve certain levels of differentiation that can be identified on a genetic level. Templeton concludes that the species Homo sapiens level of genetic differentiation is far too small for any level of taxonomy to be legitimate. In other words the human species is too genetically homogeneous for any subspecies to be identified, or as Jackson states

Our species collective origins are too recent, the extent of gene flow between us is too great, and our current diversity is too evolutionarily superficial to warrant the racial or subspecies level of differentiation among contemporary humans.[1]

Alun 21:56, 10 August 2007 (UTC)