At one point it was "universally accepted" that the Earthy and its position from the Sun was unique. A one off. Chances of another planet -IF they existed- being in the same position were "zero". Now we have a whole chunky list of solar systems with planets and also planets that seem to be in the "right" position from its sun.
At one point it was also accepted -it was scientific dogma- that water could not be found elsewhere...then we found out more about comets and Mars and Pluto and other planets/moons......water is no unique or confined to Earth.
At one point scientists stated that if -if- "intelligent life" existed anywhere else the problem of travelling huge inter-stellar distances was "insurmountable". People suggested various types of nuclear, solar or even magnetically powered craft that might make the journey -but huge ships with crews that would need to breed the next generation of crew. Or, cryogenically suspended "take over" crews. Then came the idea of worm-holes and other ways of traversing huge areas of space.
At one point scientists totally lampooned the idea that life on other planets would be humanoid. Now a great many think that human 'uniqueness' might not be so unique but might be the norm...even if not mammalian humanoid (ie. two arms, two legs and a body and head -mammalian, insectoid or reptilian it doesn't matter). It is why some of us have hunter down the alleged UFO landings involving non humanoid entities.
When you read this article remember one thing. one very important thing: we, on this planet, have never encountered extra-terrestrials that we can scientifically get data on. We have never sat any extra-terrestrial down and asked a list of questions giving us more insight into its life cycle, mental processes or its ultimate needs/goals. I am talking here about a full contact not UFO reports and certainly not what we read about "Greys".
To this you can add that we have never landed on a planet nor been beyond our solar system. As we have found on Mars, Pluto, Venus -and various moons- when we land on those in our solar system scientists have to start re-writing the text books. Pluto is NOT a huge snow-ball in space. And there is more we could learn about our own Moon (or even our own oceans).
So scientists do what scientists do: they can claim "this" or "that" because no one knows. It is mere speculation. Theory. Hot air. No more.
I recall Stephen Hawking writing that time travel was impossible even theoretically. The flaw in his argument was obvious. Yes, I did write him about this. No I never got a reply -if he even saw the letter. But two years later he had changed his chance. This is important because the average person thinks that Prof. Hawking is some totally infallible computer brained genius. He is human like the rest of us. As are these scientists with their theories.
It's all "guessology".
Is Stephen Hawking Right About Hostile Aliens?By Stephanie Pappas | LiveScience.com
"The general presumption is that this is just sort of a natural outcome of the evolutionary process, but that's really giving short shrift to the very special circumstances of human evolution," Flinn said.
Huge brains are expensive. They take an enormous number of calories to grow and function (up to 50 percent of intake in infancy and childhood, Flinn said) and make humans basically helpless for years after birth.
"Our babies are born as larvae, basically," said David Carrier, an evolutionary biologist at the University of Utah.
Many anthropologists and evolutionary biologists have tried to pinpoint the special circumstances that make these huge brains worth the expense. Charles Darwin suggested that perhaps males developed cleverness to attract females, much as a male peacock developed showy tail feathers to prove to potential mates that he could strut his stuff. But if brains were just for sexual display, scientists would expect to see big differences between male and female intelligence — females, not having to attract mates, shouldn't waste so much effort on their brains, much as peahens don't waste effort on growing shiny feathers (theirs are dull and brown). And female humans are just as smart as males.
So perhaps intelligent aliens might be subject to alien parasites. Flinn and his colleagues favor another theory, though. They argue that humanity underwent a runaway cycle of brain evolution because of hominins' social nature.
The ecological dominance-social competition hypothesis works like this: Human ancestors reached a point in which their interactions with one another were the most important factor in whether they'd survive and pass on their genes. Finding food and shelter was still important, Flinn said, but it wasn't the main factor determining evolutionary success. The difference between clever humans and, say, caribou, is that intraspecies relationships drove evolution the fastest in humans, Flinn said. A herd of caribou has social interactions, to be sure: Males have to fight for mates, for example. But a more pressing concern would be avoiding predators and finding food. For hominins, these external issues became relatively less important, the theory goes, while their ability to form coalitions, to have empathy and to behave in such a way as to win friendships from others became key to their survival.
In this heavily social context, it became very important to be smarter than the competition. Each generation got a little smarter and a little better at building complex social relationships, which created a feedback loop in which even smarter brains were beneficial.
"The thing about social competition is it's a dynamic challenge and it's also creative," Flinn said. "You need to have the better mousetrap every time. The competition adjusts to the current winning model, so you need to be one better than the current winning strategy."
The model seems to work with other clever animals, too, he added. Dolphins, orcas and chimps all form social coalitions with each other and depend on their social groups to survive. It's possible that this social factor would hold for species on other planets, too.
The evolution of aggression
A key part of this theory is competition. Chimps form coalitions that battle against other chimps. And humans are far from peaceful. So if an alien species were to evolve intelligence, would aggression be an inevitable part of the package?
Environmental factors may determine whether a mate-or-die system emerges. For example, chimpanzees are a particularly homicidal (chimpacidal?) species, Carrier said. Work by primatologist Richard Wrangham at Harvard University and colleagues finds that chimp "wars" arise from a chimpanzee's territorialism. Small groups of foraging chimps may come into contact with other chimpanzees; killing these competitors (particularly when the foragers have numbers on their side) can be beneficial by opening up access to more resources.
Deadly male-male competition is less of a way of life for bonobos, humankind's other closest primate ancestor. Male bonobos stick by their mothers and the species is less territorial than chimpanzees. Bonobo foraging groups are also larger, perhaps because their food sources are more abundant, studies have found. Would aliens act more like bonobos or chimps? Hard to say. Researchers are even split on whether humans are more inherently aggressive or inherently peaceful.
If intelligence evolves in the context of social competition, and aggression is the natural outcome of competition, it's hard to imagine that clever aliens could also be kind. Is this the end for hopes of sweet little E.T.?
Maybe not. The social competition model doesn't work without cooperation, after all. Humans fight, wage war and sometimes murder each other. But humans also form coalitions, care for each other and even build coalitions of coalitions, such as nation-states.
"There are two sides to our nature," Carrier said. "It's not that one is any more real than the other. It's just who we are."
Humans are unique among Earth life in forming long-lasting alliances between groups, not just individuals, Flinn said. Chimpanzees can't pull that off, he said, so it's not clear that aliens could, either.
"On Planet X, it may not be inevitable that social competition results in a morality and a creativity of the sort that allows these intelligent life-forms to negotiate with us for a mutually beneficial outcome," Flinn said.
On the other hand, chimpanzees don't explore space. Perhaps a civilization that can band together to reach for the stars has to be cooperative by definition. If that's the case, humanity might be a greater threat to aliens than aliens are to humanity. Luckily, evolution has given humans the tools for peace.