From Carpe Diem, a public policy blog at the American Enterprise Institute:
The chart above shows the significant, downward trend in the world’s Total Fertility Rate (births per woman) over the last half century, which has fallen in half, from almost 5 births per woman in 1960 to only 2.45 births per woman in 2010... The decline in fertility rates is also happening for reasons never predicted or advocated by Ehrlich, who proposed government solutions like population controls and sterilization. Rather, the decline has been facilitated by market-based forces like modernization, mass electrification, economic development, and television.More info (and a vociferous comment thread) at the link. Via The Dish.
But this can only be a temporary trend. While the current human gene pool may react to modernity by choosing to have only two children, natural selection ensures that the next generation will be made up mainly of those who decided to have three or four children per woman anyway. Whatever genes are responsible for that will eventually spread until the planet is pushing at Malthusian limits once again.
ReplyDeleteSorry I don't understand.
Delete"natural selection ensures that the next generation will be made up mainly of those who decided to have three or four children per woman"
-> care to explain?
"genes are responsible for that" -> for what?
OK maybe I understand the first part. You mean that countries with higher fertility end up making up a bigger part of the total population? But then what does it have to do with natural selection? But how about different fertility within the same country? Say my neighbour has 5 children and I only have 1 ; mine can still choose to get with one of those 5 and have any number of children...
DeleteNatural selection says that traits that reduce your reproduction become less common in the next generation. So imagine that you only have 1 child for purely genetic reasons -- you are susceptible to video game addiction, you are too independent to join a religion, or you are a crocodile and feed all your other children to the first one. And that it's simple Mendelian genetics -- your child with your one-child gene and the neighbor's child with the 5-child gene will have 3 children, the neighbor's other children will each have 5 children.
DeleteYour child's 3 children will each have 3, 2, or 1 child depending on if they marry someone with one of your one-child genes, meanwhile the neighbor has 20 other grandchildren who are having 5 grandchildren each. Your gene has gone from 50% of the population (you and your neighbor) to less than 8% via natural selection, because it makes you less likely to reproduce. Doesn't matter that it would have had no effect in a world without video games, or a positive effect in a world that required more parental investment to raise children to survive. In this world, it's unfit.
I hate this, but I've tried and tried to think of a way that a gene that makes you less likely to reproduce could spread. What if being childless makes you more successful economically? What if being an atheist makes you more likely to prepare for disasters? But I can't avoid the logic that any gene that makes you voluntarily lower your fertility below 2 is doomed to extinction.
OK so thanks for taking the time of an explanation. I think you're inherently wrong though on the gene thing. Not all we do in life is either foreseen by god or foreseen by our genes and I had never heard a theory of a fertility gene.
DeleteTo give you an example, my mother's parents had 8 children (7 survived into adulthood) although they were each from a 2-children family. My father's parents had 6 children (4 survived into adulthood) and would have had more if my grandmother didn't die at 33.
My parents have had "only" 4 children though, 2 of them will probably end up having none, 1 is currently expecting and might have one or two more, 1 might have up to 2.
I don't think there's a "fertility gene," obviously, nor a deterministic gene for having exactly 3 children. In the real world it would be more like a gene that makes you 10% better at delayed gratification which makes 10% of the people who have it have 10% fewer kids because they go to graduate school before starting families. I just made all the effects huge so the example would work in two generations.
DeleteAlso, genes have situational effects, like the ones that make deer more likely to have female fawns when food is scarce. You and your grandparents probably had basically identical genes, but very different environments meant that their impulses were to have many children with low investment in each while your impulse is to have few.
Noumenon, I generally agree with what you are saying, in that genes that decrease the number of children will decrease in frequency, and genes that increase the number of children will increase. Before humans knew about birth control, genes that increased the desire for sex and genes that increased the desire for children were roughly equivalent evolutionarily (once humans figured out how babies were made). However, now that we have birth control, desire for sex and desire for children are quite different evolutionarily, and desire for sex will be selected against and desire for children will be selected for. I would expect that several thousand years of evolution with birth control in the picture would make sex about as exciting as kissing. Other genes that would be selected for would be ones that make pregnancy easier (such as having smaller babies, less nasty morning sickness etc).
DeleteI would think that enjoying sex would lead to somewhat more babies even with birth control, unless birth control became mandatory and reproductive rights were issued via sperm bank. I'm not sure natural selection could catch up with that amount of change. Or cloning... basically if we became a species that reproduced asexually, we'd probably lose the desire for sex. Kind of a dystopia to me...
DeleteI agree, sex would still be enjoyable, but the genetically driven portion would put desire for it at around the level of say french kissing. With sufficiently effective birth control both french kissing and sex have a possibility of causing babies, but only at a low probability. The world's oldest profession would go out of business. Of course technology will change other aspects, as Dogbert said: When virtual reality gets cheaper than dating, society is doomed.
DeleteI'd think availability of contraceptives has had a signifigant impact on the global fertility rate. Women (and men) have a greater opportunity to decide when sex will result in procreation.
ReplyDeleteOf course this can only be temporary as well. Whether we evolve immunity to contraceptive pills, a conscious desire for children, or condom-breaking penises, from evolution's perspective contraceptives are the equivalent of cockroach poison and will not be tolerated.
DeleteOK so this confirms: I believe you don't have your science right. That's not how genes and evolution work, I'm sorry. Were you joking maybe, sorry if I missed it.
DeleteAre you just reacting to the boldness of the effects I imagined? In the real world it will probably be something quite plausible. For example, a gene that leads to 10% more risk-taking behavior will spread because people who have it don't wear condoms as often. One that leads to 10% less risk-taking behavior will shrink (until the number of additional STDs you get balances it out).
DeleteJust a short answer to both threads we are involved in: even if you downgraded those genes effects to milder effects, I still don't think you have that whole evolution & genes thing right. I agree it's a complicated and often misguiding topic though, I would simply recommend to read more about it, and since I don't claim to know everything: so will I of course.
DeleteThe sources I'm getting evolutionary theory from are
DeleteSteven Pinker's How the Mind Works
Ed Yong's Not Exactly Rocket Science
Carl Zimmer's The Loom
and TalkOrigins' Index to Creationist Claims.
It's only pop science, but I've read a lot of it.
These folks must be happy.
ReplyDelete"American Enterprise Institute"
ReplyDeleteA ridiculous propaganda mill. Wouldn't pay them much heed....
The data come from the World Bank. Are they also on your shit list?
DeleteThanks for pointing out
Delete@Minnesotastan,
DeleteYes. Emphatically yes.
http://en.wikipedia.org/wiki/World_Bank#Leadership
http://en.wikipedia.org/wiki/World_Bank#Criticisms
DeleteInteresting. I wonder why they would publish false data on global fertility.
DeleteI don't think it's false data, but The World Bank IS on my shit list and this may give you some idea why:
Deletehttp://www.guardian.co.uk/commentisfree/2009/feb/19/world-bank-reform-recession
AEI's motives are openly stated right there on their blog: Neoliberalism is great, everybody's getting richer because of neoliberalism. There are no problems. Everything's great...
Actually, I would agree with you re the scumminess of the World Bank. I just don't know whether their disastrous interventions in sovereign economies is relevant to this particular topic.
DeleteThis is hype.
ReplyDelete5 billion women having 2.5 children is still far more than 1.5 billion women having 5 each(I am guessing these numbers / did not get formal #'s from 1950 to now).
I still see the growing human population as a problem, I take some comfort in the fact that there are (at least for now) far more women with control of their bodies in determining the time of pregnancy than they did 60 years ago. So I assume a larger number of these children are living better.
Talk about unintended consequences - just wait until we cure cancer. We'll live until 130, dump carcinogens fearlessly into the ground, and... oy. I need to take a walk.
It's described as a decline in FERTILITY, not a decline in POPULATION. It will result in a slowing of the rate of increase of population.
DeleteThere are many factors affecting fertility. Counting only genetic factors or the choice of women (in traditionally high birth rate countries like Brazil) or economics driving the trend have smaller families also doesn't take into account the crap we're spewing into the environment that lowers fertility. Of course, humans may evolve resistance to Dioxin, PCBs, false estrogen pesticides, BPAs lowering male fertility, etc. Only time will tell.
ReplyDelete