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and Turkey) and the Gravettian, dated to ∼21–30 kya. These AMHs with their new style of Aurignacian- type tools transitioned along the Danube River through the regions of modern- day Hungary westward, to Austria, and to the upper Danube at Geissenkösterle, Germany. Another branch had also migrated earlier, in a southerly direction from Austria to the present- day Riviera and to the Pyrenees and northern Spain by 38 kya [31].
Genetic and Linguistic Evidence
Among our 30 000 genes, recombination and mixing of small amounts of duplications and crossovers between maternal and paternal DNA genes occurs with each generation.
However, two distinct parts of our DNA (mtDNA and the Y chromosome) do not recom- bine and hence these can be traced more easily through the generations. Mitochondrial DNA inheritance occurs along the female lineage, with males that receive it from their mother not being able to transmit to their children. All humans alive today have there- fore inherited their mtDNA from one female alive around 200 kya. The mtDNA repre- sents relative stability in comparison to changing DNA molecules, mediating inheritance characteristics. MtDNA point mutations do occur, but are rare – on average one muta- tion occurring per 1000 generations. Over a period of about 200 ky, we have each had 7–15 mutations on our own personal Eve record. We can see where certain mutations occurred, whether in Europe, Africa, or Asia. Because the mutations occur at a statis- tically consistent, though random, rate, we can approximate the time when they hap- pened. We can now trace migrations of modern humans around the planet. The oldest changes in our mtDNA took place in Africa around 150–190 kya. Then new mutations appear in Asia about 60–80 kya. This tells us that modern humans evolved in Africa and that some migrated to Asia 80 kya. In an analogous fashion, the Y chromosome is only passed along the male lineage, with the unpaired Y chromosome having no role in the exchange of DNA and playing no part in the more indiscriminate exchange of DNA by the other somatic chromosomes. The Y chromosome can therefore also be tracked relatively untampered through each generation and traced back to our original paternal ancestor [32,33].
Further support comes from the molecular clock concept tied to the natural evo- lution of DNA sequences. The postulated “mitochondrial Eve” originating in Africa approximately 180 kya was associated with a population bottleneck and very low popula- tion density, a likely consequence of Marine Isotope stage 6 climatic effects. Thereafter, two modern surviving human populations groups are recognized, genetically dating to
∼130 kya: the ancestral Khoe and San located in southern Africa, the other in eastern and central Africa. The oldest mtDNA haplogroups, L0d and L0k, are found in especially high frequencies in the Khoe–San groups of southern Africa around ∼100 kya (Figure 6.3).
These are also representative of the most penetrating mtDNA clades so far recorded among modern humans [34]. It has therefore been deduced that the L0 has a southern Africa origin, emerging from ancestral modern San and Khoe people. The evidence sup- ports the L1 originating in central Africa and L2′6 in eastern Africa within the time frame of ∼130 kya. The latter period also coincided with the extreme climate changes of cold and aridity that precipitated one of the African “megadroughts” related to both Marine Isotope stage 6 and Marine Isotope stage 5. Remarkably, during this period extensive archeological evidence of Middle Stone Age tools (termed mode 3), represented by flake tools originating from prepared cores, first appeared [35].
Linguistics provides corroborating support on the basis of click language analysis.
Tishkoff et al. have surmised that the southern African San people are “the oldest popu- lation on Earth.” Of the ∼30 different click languages recognized within the southern African region, only the present- day hunter- gatherer Sandawe and eastern African Hadzabe people have click language [36]. On this basis, it has been assumed a migration occurred originally from the south-western African region into eastern Africa [37]. This premise is supported by genetic analysis, with modern human expansion from the east- ern African region to all other parts of the world [34,38,39].
The Impact of Diet
Neurochemical Factors, DHA, Micronutrients, and Synaptic Bandwidth
Our association with DHA extends back ∼600 million years, during which time no molec- ular changes took place. In contradistinction, profound genetic changes among animals were evident during this period of hundreds of millions of years. This prompted Crawford to expound that DHA was more important than DNA and it was DHA that dictated to DNA [40]. DHA availability has an important effect on brain size and connectivity, and has many synaptic regulatory effects. In addition, AMHs have high- bandwidth synapses in comparison to rodents, and dietary omega- 3 fatty acids also have significant neural gene expression effects. When moving away from coastal and aquatic to terrestrial envir- onments, the very low availability of DHA of the land- based food chain underscores the actuality of much smaller terrestrial mammalian brains while body sizes increased. This is in part due to mammals lacking specific enzymes essential for synthesis of omega- 3 fatty acid precursors. DHA alone is not the only critical ingredient for optimal brain growth, however. Within marine and lacustrine environments, food, in addition to ample DHA,
Figure 6.3 Human evolution and mitochondrial DNA analysis:
diagrammatic depiction of the predominant, presumed mtDNA haplogroup LO migrations (ka, thousands of years ago).
Source: figure with permission from Rito T, Richards MB, Fernandes V, et al. The first modern human dispersals across Africa. PLOS One 2013;8:e80031. https://
doi.org/10.1371/journal.pone.0080031 Reproduced under the CC BY 3.0 https://creativecommons.org/licenses/
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