Evolution of mammals , theories etc

I’ve been reading a short description of the debate between multiregional and single point camps concerning homo sapiens evolution. This could be a great debate, but it’s not my question.
The question is, have there been any cases of an animal of similar type developing in a multiregional manner?In other words, developing in different parts of the world from a lower animal (mammal, or other). It does not seem to make a lot of sense.
The multiregional theory seems to be the older one, when race in man, for instance, was thought to imply great differences.

The short answer is no. There are very few mammals that have as large a range as Homo sap (in fact, aside from our hanger-on like dogs and rats, I cannot think of any). Now, the legitimate question is whether the change from H. erectus to H. sapiens was an example of phyletic evolution throughout our range (Africa through Asia at the time). Given our propensity to travel and interbreed, I don’t think there is any great objection to this scenario. Personally, I think the change from H. erectus to H. sap was an allopatric event, probably in the Rift Valley, and the saps moved out and displaced the erectus throughout their range, and extended the range to Australia and the Americas.

It has always struck me as a trivial question, and it seems to only be of interest to those who wish to place as much distance as they can between themselves and other regional variations of our species. But these folks miss the point; if different populations of H. erectus developed into H. sap independently then interbreeding would be impossible. Either legitimate scenario shows that all humans are very closely related, and “racial differences” are superficial variations of each other.

Are you saying an H. sapiens individual couldn’t breed with an H. erectus individual? I kind of always thought they could but I don’t have any evidence for it. Is it common knowledge that they couldn’t?

I know different species aren’t supposed to be able to interbreed, but some species can … housecats and a large feline form fertile Bengal cats, after all.

The reason I ask is, if H. sapiens was just an H. erectus with really competitive genes, maybe they could have developed in several places roughly contemporarily, and then outcompeted their H. erectus cousins. That notion might be completely bogus though.

Typically species are thought of as being reproductively isolated, but there are some anomalies. Also, from what I understand “reproductively isolated” doesn’t necessarily mean “can’t interbreed”; two species could be genetically compatible, but isolated because of geography or behavior.

However, in the case of extinct animals it’s sort of a moot point: there aren’t any around anymore, so we can’t find out if they’re cross-fertile with their nearest surviving relatives or not. We have to guess based on other criteria, such as cranial capacity.

As far as the isolation part goes, are there animals on Australia that do interbreed with cousins on another continent? Aside from birds.

The population of homonids which became what we recognize as H. sap began as a variant of the H. erectus. The question is merely whether the change to sap took place in a relatively small sub-population which then displaced the erectus throughout its range or if it was the entire population which shifted. I support the allopatric scenario for two reasons. First, because that is how we observe speciation and population turnover in every other type of animal. And secondly, although this is based upon negative evidence, if the change took place over the entire population we would have the reamins of at least some individuals “half-way” there. A small initial population is far less likely to be caught in the act of a morphological change in the fossil record.

At some point the population which would become sap could interbreed with the dominant population. But its peculiar adaptations would have been swamped out by the volume of the gene pool. If this happened several times then we would have a multi-regional type of emergence, but I think the number of dilutions needed to affect a wholesale change in a world-wide population are unreasonable given the time frame observed for the turnover.

The timeframe argument is what I’ve usually heard.

But back to the critters. I vaguely remember reading in Biology 101 about some species of birds, fairly far North. There was a circle of related species around the globe, and each “species” was able to mate with their two neighbors, but with none of the others in the group. Does this phenomenon have a name?

“Ring species”

You are probably thinking about the Larus group, seagulls which live around the Arctic ocean. The British lesser black-backed gull can breed with the Scandinavian lesser black-backed gull, which in turn can breed with the Siberian vega gull, which breeds with the American herring gull, which is interfertile with the British herring gull. But, the British herring gull is unable to breed with the British lesser black-backed gull. By one crtierion, the two British species must be considered subspecies of the Larus gull species, but since they are reproductively isolated (although sharing the same environment) they must be considered seperate species.

This happens often in nature. Usually a chain of sub-species, each showing slight regional variation but able to interbreed with their neighbors, will form along a mountain range or some similar obstacle. If the sub-species at the ends of the chain are not interfertile the arrangement is called a cline. This is the sort of thing that makes taxonomy interesting.

I could go on for hours…

Oh, and the animals which are native to Australia have no close relatives anywhere. None of them can interbreed with anything from anywhere else.

I’ve never attended a formal course in biology in my life, so maybe that’s why I have trouble putting your posts here together reasonably, or maybe it’s not.

It appears overall that you believe sapiens evolved from erectus in comparatively short order, only once, in one geographical location, and you suggest the Rift Valley in East Africa for this. It appears, then, that you further believe that sapiens soon thereafter was able to overtake and replace erectus at all other locations on the globe where the latter existed. That all sounds to me like the most probable scenario of those presented here.

But when I look at the specific wording of your first two posts here, I don’t understand it. ‘Allopatric’ refers to simultaneous ecological change over a wide range of geography, doesn’t it? But at the same time you say you hold for the allopatric view, you describe the species change as localized and spreading only thereafter universally.

BTW, noting the discussion here of what you term “ring species”, what’s your view of changing biological taxonomy to such a new system as this?


Sorry for jargon, nano. “Allopatric” literally means “in another place” and refers to the concept that physical separation was needed before reproductive isolation could occur.

Maybe the BioCode provisions will bring those radical botanists in line so everyone will know what they are talking about. Plant people are weird.

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
Cave ab homine unius libri

Do I misremember entirely, or has the same “multi-regional vs. single point evolution” question come up concerning the H. sap. to H. sap. sap. (that is, “Neandertal” to “Cro Magnon”) replacement? Perhaps you could comment.

That was the point that I didn’t want to become a Great Debate. But if you read Fidelius above, there is discussion of that question.

I checked out a small Barnes and Noble science section. It’s about half the size of the Ne Age and Self Help sections.

There were a few books about human and other evolution. Quite a few books by an author named, I think, Gould.

I found a good revie of Stringer, which I’ll post if I find it again. A book by Tattersall , the Fossil Trail, seems to be available for about $13.I don’t know if Dr. Fidelius rates it highly or not.

(The Eve Hypothesis) http://archaeology.miningco.com/education/socialsci/archaeology/blpaleoraceweb.htm
(a bunch of links) http://www.icr.org/pubs/imp/imp-141.htm

This I thought was a pretty good review: http://www.newscientist.com/sciencebooks/reviews/africanexodus.html
Although the multiregionalists tear this book apart under Amazon reviews.

If someone wants to debate this further, you may wish to leave a note here and start a topic under Great Debates.

I’m still interested in the critters. Take some simple animal such as a deer, which are found on many continents. How many species are there, and how long did it take for them to become species (that can’t interbreed)?

My only recommendation for reading is to read everything. Then, after fifteen or twenty years you should be well enough informed to make your own interpretations…

Oh, I have no opinion whatsoever on the replacement of the Neandertals by Cro-Mags in Europe and the Mediterranean. There are too many factors involved in any faunal succession, and just because the species involved in this case are our relatives doesn’t make it any more interesting to me. You want something interesting? Check out the Wallace Line…