They walked. A landbridge was exposed due to low sea levels. The same way UK/North America was populated.

They wandered over from somewhere in India a fair while ago (but not as long as they think). Perhaps 50kya they wandered across the exposed (due to low sea levels caused by ice age) land bridge from India to Northern Australia. Once there they started acting like abos, setting fire to shit and killing off all of the large animals. By about 45kya there were effectively no animals bigger than an adult human in the South West of the continent. The abos ate the eggs of giant flightless birds, and hunted the megafauna (likely targeting the more easily overpowered juveniles), leading to a demographic collapse in populations. This is evidenced by fungal spores that are found in sediment layers, these fungi were adapted to growing in the droppings of megafauna, and abruptly disappeared around 45kya, a time when no significant climate change was effecting the area. The only likely explanation is predation by aboriginals. You certainly won't find this information at any museum, where they worship the ground that abos walk on and fucking hate White men. The museums will usually blame "climate change", ironically providing an argument against the supposed "bad White man climate change".

There were probably earlier migrations of even more primative hominids but these were either gone by the time abos arrived or displaced/interbred with them. The abos first migrated out of Africa, without interbreeding with either Neandertal or Denisovan species. Whether they interbred with the as yet unknown hominid that Africans did is not really clear, but their lack of either Neandertal or Denisovan interbreeding likely explains their remarkably low average IQs (62).

They flew there in the dreamtime.

They may have been smarter in the past but rampant inbreeding has fucked them up. I don't know, just a theory.

My guess is that they've always been there, like niggers in Africa.

Modern day Filipinos are most closely related to the first known inhabitants (Denisovans) of Australia that arrived approx 40,000 years ago. They spread widely, but then declined, then the modern day Aborigines came in more recently (who were also in decline in most of Australia and wouldnt have lasted much longer. Probably because of their habit of burning everything in sight, and destroying the local habitat until it couldnt sustain them, and then moving on to the next patch to do the same. I havent seen much information on the Denisovans, because apparently it's racists to think about the truth, as modern day Aboriginees have declared themseves the first nation, first people, and all that arrogant nonsense. It keeps the lawyers fed.

Evolution happens very quickly. people think it happens slowly but it depends on what kind of change. A fundamental change like growing an extra set of arms would take forever since it is creating something entirely new. But changes in size and intelligence can happen after a single generation.

Something catastrophic like WW2 can wipe out certain genes within a population and leave the remainders as entirely inferior to the population only a single generation prior.

Aboriginals Likely "dumbed down" after reaching australia due to the continent being so dangerous. Anyone with adventurers spirit and the will to cross the oceans would quickly die to poisions from strange sources like platapus stings. Curiosity would have died off fast and anyone who simple survived living a lazy life style would have been left over.

Thirteen thousand years ago the earth passed through the tail of a comet and earth was bombarded my meteors. That caused the sea levels to rise 300 to 500 feet in the matter of months.