Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Airthumbs on 07/05/2012 00:03:52
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What factors would define a new species of human, and could just one trait such as intelligence be one of those factors.
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A 'species' is one of the most difficult things to define in Biology and based on conventions.
I believe, one of the conventions for mammals is that two species cannot produce fertile offspring, so to answer your question: If a group of humans evolve from the Homo sapiens sapiens that can make fertile offspring amongst each other, but no longer with Homo ss, then that would be a new species.
If you're talking about a new species of hominids evolving from primates, then indeed intelligence will matter probably, but I think they'd never be called hominid because we humans are too vain for that ;)
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I think you would need a significant isolation, separation, or bottleneck event.
Certainly if there was a chromosome split or fusion, so that "new humans" would be incapable of producing fertile offspring with "old humans", then one might name it a new species, especially if both exist concurrently.
Racial diversification from about 20,000+ years of previous separation was not considered sufficient to declare independent species existing on the different continents. There certainly are more similarities between all current existing races, than between humans and Neanderthals. However, there are also morphological including skeletal differences between races that go beyond skin tone, so to a large extent, races could be determined from merely looking at skeletal structure.
Intelligence has been increasing, and other factors may also be slowly drifting. However, many of these may be due more to education, nutrition, and medicine, than any species change. And, of course, there is a range of IQs, even within a single family.
Perhaps in year 200,000, future humans will look back and declare themselves members of a new species distinct from homo sapiens. However, it is likely the division between the two will not have occurred in a single moment, but rather a long transition period, perhaps even during the entire 200,000 year period. That is, unless, there is a traumatic event creating a bottleneck in the species.
Will future humans choose to tinker with our genes? Perhaps making genetically modified spacefaring hominids? Or better aquatic adapted humans? In which case, these new genetically modified humans might be considered a separate species.
Or, will future humans choose to seed other stellar systems with humans and earth life? Potentially in a manner where interstellar travel would be very rare, or possibly only happening once for each star system. In which case, one would naturally have the isolation, separation, and bottleneck events. Over hundreds of thousands, or millions of years, the earth, and distant star populations would naturally drift apart.
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I think I would have to agree with Nizzle. There would need to be two homonids which cannot interbreed.
BUT, we are evolving, so could we now interbreed with our early ancestors? In another ??? years will they be beyond the capability of breeding with us? In other words, when do we declare ourselves to be no longer Homo s. but evloved into Homo ??
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There are several theories that homo sapiens could in fact interbreed with Neanderthals... well, we could if we hadn't killed them all off.
Archaeologists use time, distance, and morphological features to determine separate species. With human ancestors, the Chromosome 2 fusion (http://www.evolutionpages.com/chromosome_2.htm) would make a major division in hominid species, and dividing into two major species, the pre-chromosome 2 fusion, and post chromosome 2 fusion groups (does anybody know when this occurred?)
It is quite likely that if there were multiple concurrent hominid species, they might have been able to interbreed, if both subspecies carried the same Chromosome 2 fusion (or lack thereof).
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Whats chromosome 2 fusion?
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Whats chromosome 2 fusion?
Humans have 23 pairs of chromosomes. Chimpanzees and great apes have 24 pairs of chromosomes.
Comparing Human Chromosomes to Chimp Chromosomes, the two are very similar, except Chromosome 2.
http://www.thetech.org/genetics/ask.php?id=264
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thetech.org%2Fgenetics%2Fimages%2Fask%2FhumanChimpChromosomes.gif&hash=e6a76f6320e3cda8ca7f4c6786ab74db)
Chromosome 2 appears to be in two parts in Chimps, but one part in Humans.
So, the question is whether the chromosome originally was intact and split in half in the apes, or if it was two chromosomes and merged in humans. The answer lies in telomeres.
DNA transcription is unable to transcribe chromosomes all the way to the end. To get around this problem, telomeres (http://en.wikipedia.org/wiki/Telomere) are added to the ends of DNA strands. It is essentially a repeating sequence, TTAGGG, so it is the marker for the end of the gene sequences.
And, in fact, in the middle of Chromosome 2, part of a telomere exists. So, one must conclude that this telomere was in fact once at the end of the chromosomes, and that two independent chromosomes must have fused.
I don't think anybody knows for sure when this fusion occurred. However, it is not in any primates, so it had to have occurred after the last common ancestor for the hominids and primates.
Consider the Equines, Horses, Donkeys, Zebras.
A horse has 64 chromosomes. A donkey has 62 chromosomes; the zebra has between 32 and 46 (depending on species).
A cross between a horse and donkey would have 63 chromosomes, and different equine crosses produce different numbers. The mule receives a half a set of horse genes, and a half a set of donkey genes, but generally a full compliment of genes from both species. Mitosis can reproduce the cells with an odd number of mismatched chromosomes (63).
Meiosis, however, is unable to match and divide the genes for reproduction due to the odd number of mismatched genes.
Thus, the mules inevitably are sterile.
This fusion would then be one of the greatest obstacles for interspecies breeding.