The Out of Africa theory is the dominant model of the geographic origin and early migration of anatomically modern humans (Homo sapiens)(a). It arose from discoveries in East Africa less than a century ago. Previously, a more popular idea prevailed which claimed that modern humans arose from different populations of earlier hominids in various regions of the world. This regional development still has some advocates(h)(c).
A 2007 report deviated somewhat from the OoA concept, and suggested that the first Europeans had arrived from Asia, rather than directly from Africa!(f)
While details of the OoA theory are continually being modified in the light of new discoveries, genetic studies have only strengthened support for the theory. The most recent genetic studies suggest that “a vast inland oasis in present-day northern Botswana was once home to the founder population of all modern humans.” (b)
New studies suggest that the early development of homo sapiens may have been more complex than previously thought(e). Chris Stringer, of the Natural History Museum, London, is quoted by The Guardian as saying that “the immediate predecessors of modern humans probably arose in Africa about 500,000 years ago and evolved into separate populations”.
It is still uncertain whether humans left Africa in two or more waves and when did they do so. Stephen Oppenheimer, who has written extensively on the subject, maintains that a single group of migrants were involved, around 80,000 years ago. He offers several papers on the Bradshaw Foundation website(d).>Current opinion favours Bab-el-Mandeb at the south of the Red Sea and the Sinai Peninsula at the northern end, as the most likely exit routes.<
In the September 2021 issue of Nature, evidence was presented that hominins had migrated out of Africa to what was a much greener Arabia, in a series of movements starting approximately 400,000 years ago and later around 300,000, 200,000, 100,000 and 55,000 years ago, coinciding with successive periods of more benign climate on the peninsula(i). Later in the year, another report endorsed the importance of Arabia, describing it as the “cornerstone in early human migrations out of Africa.” This was the conclusion arrived at following the largest-ever study of Arab genomes(j).
As I see it, dating the spread of humans remains unclear to a layman such as myself. Of particular interest is determining more accurately when man first crossed the Bering Strait from Asia into America.
Not directly related to this subject but nevertheless interesting is a recent research report published in the Journal of Mediterranean Archaeology(g) (2021 DOI: 10.1558/jma.18784), which deals with Mediterranean migration trends over 8,000 years. It found that, within the region from about 7,500 BC to AD 500, migration rates ranged from about 6% to 9% of the population within the dataset. These rates seem to have decreased over time and “that despite evidence of cultural connections, there’s little evidence of massive migration across the region.”
A 2021 article in the Smithsonian Magazine reviews recent theories regarding much earlier migrations of hominins, particularly Homo erectus(k).
Seafaring and Atlantis are inextricably linked. In Critias 117d Plato anachronistically refers to the shipyards of Atlantis being full of triremes, which were not developed until the 7th century BC, long after the demise of Atlantis. However, the term ‘trireme’ was probably employed by Plato in order to make his narrative more relevant to his audience. He credits the Atlantean navy of 1200 ships, which for me seems like borrowing and rounding of either the Achaean fleet (1186) in Homer’s Iliad or that of the Persian invaders (1207).
Seldom referred to, but perhaps even more interesting is to be found earlier in Critias 113e which reads “for at that time neither ships nor sailing were as yet in existence” in reference to the origins of Atlantis. However, we are given little information to bridge the time up to its development as a major trading entity. It is reasonable to assume a gap of several thousand years.
Recent studies(a) have suggested that primitive seafaring took place in the Mediterranean thousands of years earlier than originally thought and may even have been engaged in by Homo Erectus and Neanderthals in the form of island hopping and coastal-hugging, the latter continuing into historical times.
Plato’s describes an advanced maritime trading nation with a powerful naval capacity. How much was part of the original story brought from Egypt by Solon or if it was in any way embellished by Plato is unclear? The earliest known trading empire is that of the Minoans which began in the 3rd millennium BC and has led to many identifying them with the Atlanteans. However, there are very many other details in Plato’s narrative that seriously conflict with this hypothesis.
>The limitations of ancient seafaring raise many questions regarding the navigation supports available to these early sailors(b). Initially, sailing, probably for fishing, would have been confined to daytime travel and keeping within the sight of land. With the development of maritime trade, the demand for improved navigation methods also grew.
In time sailors acquired a familiarity with the night sky that enabled them to used the stars as navigational aids, given clear skies. Gradually, as nighttime travel became more common, the use of beacons and later lighthouses also expanded. The lighthouse at Pharos near Alexandria came to be counted as one of the wonders of the Old World. Similarly, it is thought that the Colossus at Rhodes performed a similar function.
Different navigation skills have been identified in different parts of the world. In the Pacific, the navigational capabilities of the Polynesians are legendary(c). The ancient Chinese employed magnetism(e) and in the cloudy North Atlantic, the Vikings used their ‘sunstones’(d).
In their book, Atlantis in America  Ivar Zapp & George Erikson claimed that the stone spheres of Costa Rica had a navigational function[p34] as Zapp discovered that the sightlines of all the stones remaining in their original positions, did point to important ancient sites such as Giza, Stonehenge and Easter Island!
A most imaginative proposal has come from Crichton E.M. Miller who has proposed  that the ubiquitous Celtic Cross is an image of an ancient navigational device. He further claims that “This instrument can tell the time, find latitude and longitude, measure the angles of the stars, predict the solstices and equinoxes and measure the precession of the equinoxes. It can also find the
ecliptic pole as well as the north and south poles; it can make maps and charts, design pyramids and henges and—used in combination with these sites—can record and predict the cycles of nature and time(f)“. Then for good measure, he proceeded to patent the device.<
(f) Atlantis Rising magazine #35 http://pdfarchive.info/index.php?pages/At