Other events (if in the next decades) that might kill billions of humans:
- meteorites.
- super volcanoes.
- any combination of them.
There is nothing else that could happen for real that would harm humanity to a catastrophic degree.
No asteroid large enough to kill billions of humans is likely to impact Earth in this century. After that, it's likely that humanity will be so advanced that it'll be able to either mitigate or deter an impact of any magnitude.
An overlooked possibility imho would be a catastrophic population decline[1]. Basically women not having children anymore. Japanese style, only worse.
It's difficult to imagine it leading to extinction, since there will always be groups, at the very least religious groups, who will keep having babies. But still, it wouldn't take much of a cultural change for it to expand to all women.
Not saying it's plausible, but to me in terms of population dynamics it's at least as much of a concern as climate change (by this I mean that I believe reproductive behavior will have more impact on demography than climate change).
I can not imagine that lack of babies could ever become a problem for humanity until humans decide to build humans so that the "natural human species" dies out.
The solution for the aging population:
- Automation.
- Biochemical solutions and genetic engineering to remain/become capable. Replacement of natural body parts by machine body parts.
Worrying about overpopulation is short-sighted. Also, no matter what kind of problems overpopulation brings, it's hard to imagine how that could lead to extinction, which is what we were discussing.
I hope that poverty and the culture to have as many children as possible will not exist anymore after 2030 CE.
Pollution and resource scarcity are the obvious limits that can send population numbers off a cliff.
That the desire to "not want to have children" (especially among women) exists at all is caused by the sexual revolution (contraceptives), which changed who had children from "people who desired sex" to "people who desired to have children."
Maternal instinct exists : it pushes a woman to keep her offspring alive at all cost. I suppose it also makes women yearn for having a baby to take care of. But apparently, having just one is enough for them. Maybe two, but they seem to be content with no more than that.
What makes a woman pregnant in the first place is the sexual impulse of the male. That sexual impulse is the primary way nature gets animal organisms to reproduce. With contraceptives, males can satisfy that sexual impulse without creating new offspring. How will nature induce highly-intelligent animals to make an offspring if the sexual intercourse is no more sufficient? It's hard to imagine how genes could intervene high enough on cognitive functions to induce a thought such as "I must have intercourse with this women without contraception because I want children".
It could be an evolutionary dead-end.
My point remains anyway : even if there was a perfect symmetry in gender roles, parenting instinct would be what makes parents desire to have at least one offspring and keep it alive at all cost, but what would drive them to have more than two would be sexual impulse.
"As of 2010, about 48% (3.3 billion people) of the world population lives in nations with sub-replacement fertility."[1]
It's culture and education
https://www.ted.com/talks/hans_rosling_on_global_population_...
I can tell you that my wife and I both knew long before we were anywhere near adults that we wanted families. You know how some people know that they want to be a fire fighter or a police officer when they grow up? I knew I wanted to have a bunch of kids. The story is more or less the same for her. And my wife and I both grew up on the left, where the attitude toward having children varies from something you do after you have your career sorted to outright anti-natalism.
We're not zebra and lions
> knew long before we were anywhere near adults that we wanted families
peer pressure is strong in our society
family is a motivation to stay alive for many
> I knew I wanted to have a bunch of kids.
Yeah I though I knew as well, much like I thought I was going to be an astronaut
Now I'm a grown up man, in charge of his life, and I know I don't care about a family
And it's not the gene's telling me, I still think about having a legacy, a mini me persisting my DNA but I know that it's just a legacy from the past where a man without a family to support wasn't a real man.
That's it, education and culture
If reproducing was such a strong genetic trait, men on heart would have been billions centuries ago
The truth is kids are family support, the more societies get rich, the less people make children
It's scientifically proven, poor need kids not for reproduction but for elderly support
Poor also make a lot of children because in poor societies kids die more easily
The idea that complex behavior can be caused by genes in animals, but somehow not in humans is incorrect. People point to culture as if it is some magical force that makes people do things, but the human ability to create and interact with culture is itself the result of genes. After all, zebras and lions don’t have culture.
And you missed my point: I grew up in a culture that did not value having children. Having children was considered an after thought, something to be done after you had attended to your career. Growing up, I only knew one family with 4 children. They were considered the weird religious family. Yet I have known since I was 12 or 13 that I wanted to have a large family, even though I grew up in a culture that would look down their noses at a family of 4 or more children.
And the argument that poor people have lots of children for financial reasons doesn’t hold up any more. It did when most people were farmers, but the poor in the developed world are no longer farmers and I don’t think there’s any way to argue that children are a net financial benefit to them.
that's not true!
It's not even the main drive for many apes and monkeys…
> The idea that complex behavior can be caused by genes in animals, but somehow not in humans is incorrect
But I didn't say that
I said we are not those animals and don't live by the same rules
The complex behaviour of catching a mouse in a cat is genetic
Should humans behave the same when they see a mouse?
> I grew up in a culture that did not value having children.
Oh that's even more powerful
Youth rebellion
Do exactly the opposite that your parents and people around you are doing
> And the argument that poor people have lots of children for financial reasons doesn’t hold up any more
It does now more than ever
Now that globalization is taking a lot of poor countries out of poverty
Just watch Hans Rosling's talks
Easy: being on top of the food chain allowed us to evolve our relations beyond having an offspring
Those having more satisfactory relations formed groups that we now call families up to the point where sex today is mostly recreational
basically pleasurable sex gave us mate choice just like a bird chose the best dancer or a lioness the stronger male
pleasure instead of strength in the long run made happiness a goal in our modern societies instead of simply domination
we don't have sex just in some period of the year
we enjoy sex just like we enjoy eating or having fun
For a cat or a dog sex is not pleasurable, it's just a relief from heat, but we call it rape.
This is only the case if the selection pressures which humans in the developed world are facing stay the same. Since they seem to be tied to our technological development, I think there is a good argument to be made that these selection pressures will intensify as we breed resistance to them. My personal theory is that the increasing addictiveness (see the PG essay on this[0]) of modern life is why people are having less children. I don't see that trend changing.
I do think there's a good chance that technological renunciation and voluntary cultural isolation of some sort are the best solution to this problem for people who are naturally susceptible to the addictiveness of modern life.
At space there are some pan-galatic killers, nearby supernovas (no idea where is the closest candidate), and a black hole could always cross our path without any warning.
The effect of a black hole's gravity on distant objects is exactly the same as the effect of any other object with the same mass. It would disturb Kuiper belt objects that everyone's watching very carefully these days, affect the orbits of the outer planets as it moves closer, and bend light around its event horizon in a very obvious way.
Whether we can do anything about it, of course, is a different problem.
With regard to climate change: We know the danger is real and thus humanity adapts to prevent the worst.
That basically leaves the US or Russia (the only countries with the capacity to do so) arbitrarily deciding to nuke most cities in south Asia.
That said, I don't see any objective (rational or otherwise) of either country that would be advanced by such an attack. And again, we're talking about an attack that will kill 1B+ people, not just any nuclear attack -- that's a different story. Still low probability, but at least there are semi-rational objectives that could motivate it.
https://en.wikipedia.org/wiki/China_and_weapons_of_mass_dest...