They Don't Make Homo Sapiens Like They Used To | Human Evolution

Finally, it's being recognized. Thanks for posting this. I've been waiting for this for years.

Actually, this doesn't surprise me at all. My contention has long been that there has only ever been one species of hominin and that it is polymorphic. Polymorphism is the ability to evolve into many forms. In the evolutionary process, the presence of two or more variations of a genetic characteristic is due to the appearance of alternative forms of genes located in specific positions on specific chromosomes that are responsible for variations in DNA structure, like the different human blood groups. Polymorphic variations are distinct either in appearance, constitution or both and are the result of interaction between the species’ genetically determined characteristics and the environment. Phylogenetic polymorphism in a species is the presence of more than one type of appearance or constitution and is due to the transitional status of the genetic characteristic. In essence, these variations identify progressive stages of transformation and adaptation within the evolutionary history of the species.

Our most immediate ancestor, H. heidelbergensis, is itself not even recognized as a separate species. Katerina Harvati of the Max Planck Institute for Evolutionary Anthropology says, “Middle Pleistocene specimens commonly attributed to H. heidelbergensis show Homo erectus-like features, but also some modern human-like characteristics. Perhaps most importantly, they exhibit an increase in brain size and encephalisation, and concomitant changes in skull shape. Throughout the last century, H. heidelbergensis has been the subject of controversy, with some researchers placing it within H. erectus, and others recognizing it as an archaic form of our own species, H. sapiens. More recently, it has been accepted as either the last common ancestor to both Neanderthals and modern humans, spanning Africa, Europe and perhaps Asia, or as a chronospecies of the Neanderthal lineage restricted to Europe.”

From this it is obvious that H. heidelbergensis cannot be easily identified – nor easily dismissed – as any one of three different species. Specimens have been dated from about one million two hundred thousand years ago to the appearance of anatomically modern humans, a period in which all three of the other species – erectus, neanderthalensis and sapiens - are known to exist. So, while a chronospecies is one which evolves physically, morphologically, genetically and behaviorally in such a way that the original species and its subsequent descendants would not be classified as being of the same species had they existed at the same time, there is only one type of the chronospecies lineage alive at any time throughout this change. This alone makes H. heidelbergensis’ status as a chronospecies unlikely. There is even disagreement that the species was restricted to Europe, though the majority of the finds so far are from that region.

A recent genomic analysis of human X chromosomes identified at least one lineage that has survived for over one million years without any clear trace of ongoing recombination with other lineages. This study concluded that the human gene pool and genetic structure predates the anatomically modern human. This conclusion supports human evolution models that incorporate interbreeding between divergent branches of the genus Homo although the X chromosome data cannot establish when the interbreeding may have occurred. It may be that the modern human physical type arose first and interbreeding occurred as a consequence of the rapid expansion of the population. Alternatively, the modern human physical appearance may, itself, be the by-product of interbreeding. In either case, while the majority of the anatomically modern human genome may descend from a single population in Africa, the evolutionary lineage leading to modern humans did not develop in reproductive isolation from other archaic hominin subpopulations and, thus, cannot be considered a distinct biological species. In other words, H. sapiens has now attained the same debatable status as H. heidelbergensis.

Other recent studies confirm the extended genetic lifespan of modern humans. The coalescence time for a variation of the ms205 minisatellite gene system found among Basques, Japanese, British and Africans is estimated as about one million thirty-two thousand years. One million years ago, the only hominin on earth was Homo erectus (and, arguably, Homo heidelbergensis), which means modern humans are genetically descended from this archaic species. Additionally, human DNA sequence variation data from a noncoding autosomal region estimates the age of the most recent common human ancestor to be one million two hundred ninety thousand years ago among the African sequences and six hundred thirty-four thousand years ago among the non-African sequences. This data demonstrates the high likelihood of independent genetic lineages stretching back long before the first known migrations out of Africa by modern humans.

These new discoveries in the field of genetics suggest that Darwin’s replacement hypothesis does not apply to a polymorphic species such as ours, at least during the stages of its evolution when the frequency and extent of variation in its form and structure is greatest. Over the last ten years, evidence of interbreeding as late as forty thousand years ago between modern humans and archaic species that were long believed extinct raises more questions than answers about the origins of modern humans and the extent of speciation within the genus Homo. The question to be addressed now is whether all Hominins from erectus forward are actually different species or simply related branches of the same species that are capable of interbreeding.

these mutations seem to be piling up faster and ever faster, like an avalanche. Over the past 10,000 years, their data show, human evolution has occurred a hundred times more quickly than in any other period in our species’ history.

This stands to reason in my thinking ....... because the larger the total population becomes ... the greater the chances of passing on the mutations in one group ...... to members of another group.

Also, it stands to reason .... that the more complex a species becomes ..... the less likely a body modifying mutation will be passed on to any offsprings because the individual itself is not likely to survive pre-natal development if said mutation affects any critical organ or body system.

Just my thoughts.

Why would evolution, human or otherwise, ever be considered over? It seems as if evolution is a process and this process is not over and won't be until the end of time.

Nice post...Actually this ties in to a recent publication in PLOS discussing one of the mechanisms believe to be involved in this accelerated change...

"Hotspots of Biased Nucleotide Substitutions in Human Genes"

http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.1000026

Great article, crazy that blue eyes have only been around in the last 1/5 of human existance.

well, we are continuing to evolve. It may be that the process of evolving and the preponderance of observed mutations might be the "norm". We must bear in mind, that even as we find new variances in human evolution, there are a number of existing varieties of lifeforms that also show a long process of divergent variations in their evolution.

This article and the posts are amongst the better i've read through.