Farming to blame for our shrinking size and brains

Ok this article contradicts itself several times

These scientists are plain stupid, they just cant get their head out of their asses....they know shit about biology!

"While the change to agriculture would have provided a plentiful crop of food, the limiting factor of farming may have created vitamin and mineral deficiencies and resulted in a stunted growth."
and then
"Agriculture however does not explain the reduction in brain size. Lahr believes that this may be a result of the energy required to maintain larger brains."

So they find it really hard to explain why body shrink and the head does the same:))))))
Go to school!
It is not lack of energy that have shrunk the body, actually agriculture give more energy than hunting.
Humans back then needed robust features to bring down the megafauna living back then, without the help of iron and stuff , just wood and stone, now a regular tribe of skinny massai can kill an elephant easily, but they have iron.
It is really stupid to explain something without accaunting all factors

Ok this article contradicts itself several times

And was obviously not proof-read...

"Within the last 10 years, the average human size has changed to a weight between 154 and 176 pounds and a brain size of 1,350 cubic centimeters."

Which would be very worrying if true! ;-)

These scientists are plain stupid, they just cant get their head out of their asses....they know shit about biology!

They never said it was a lack of energy that shrunk the body. Yes agriculture likely provided more energy, but only in limited form. Rather than a variety of foods, they were limited to what they could grow. There was no farmers market. This limited variety may have resulted in vitamin deficiencies. Also please understand that crops at that time were not the same form as today. It took thousands of years of selection and breeding to get where we are now. As for the reduction in brain size, I think they are saying that statistically agriculture has not shown a significant effect. Rather it was likely evolution acting as it always does. Variation in brain efficiency within a population, those with more efficient brains had more energy to work, collect food, and breed, thereby passing this efficiency on to the next generation. That is how I read it anyways.

Yeh my favorite rating someone and then go.
If you dont agree then argue with me, what kind or rats just rate and then go?

I was refering to the part where they "explain" the part where the body get smaller but then they say- it is unclear why the brain does, well havent they heard about human proportions, smaller people have smaller head, and smaller brain, why they separate the body and the head, how stupid is this, and then all the speculations we are getting more stupid!!!

Before agriculture, humans ate a high protein, high fat diet. And not just any protein or fat. Grass fed animal fat is of much higher quality than grain fed.

I was refering to the part where they "explain" the part where the body get smaller but then they say- it is unclear why the brain does, well havent they heard about human proportions, smaller people have smaller head, and smaller brain, why they separate the body and the head, how stupid is this, and then all the speculations we are getting more stupid!!!

Yes that is true in general. But there is no rule that one cannot have a small body and large head, correct? Or large body and small head. Humans are attracted to symmetry, and I would guess having even proportions as well, which would explain why today most people have heads and bodies that are proportionate. Basically I am saying that these "rules" are not set in stone. Obviously brain size is limited by skull size, but only to the extent of how large it can be, not how small. Brain size can be independent of skull size taking into account this limitation.

When they find skulls they drive conclusions about the brain size, based on these skulls, they dont find brains.
And body size is not accurate yes, if you are fat this wont give you bigger head, there are different proportion standarts for different races and different subraces, but the main rules are, that tallness is not linked with the head size , but how broad your bones are, not how long they are, also.
And what is more likely the whole human proportion pattern to be changed or just how big you are- like the dogs, big dogs have big head, small one smaller head smaller brain, so all this conlusions especially the last one:
"Agriculture however does not explain the reduction in brain size. Lahr believes that this may be a result of the energy required to maintain larger brains. The human brain accounts for one quarter of the energy the body uses.Human brains have evolved to work more efficiently and utilize less energy. "
Is pure shit, made by ignorant people!

Humans now are not that different from the people living 10 000 y. in the past, you may find unreduced people even now, big with big heads, and their brain is not less efficient or something.
Some pseudo scientists just have to go to plant potatoes instead of talking nonsense.

Even today, women malnourished as children can die in childbirth when the babies head is too large for their stunted frame. Evolutionary pressure for smaller head size probably continues in some third world countries.
It would be interesting to see how our brains evolved genetically over to last 10,000 years to compensate for the smaller cavity.

Deesky I dont give a f. about your ratings, but if you think I am wrong somewhere just post your view, otherwise you are just stupid rat, so ratings from people like you dont bother me really.

That is pretty worrying that the Human brain size has shrunk over that span of time. I don't know, necessarily, if that's such a good thing. Current science would have us believe that bigger brains (rather than brain structure) is associated with an increased "intelligence".

How much of that 150cc change was neuroglia?

This reduction in brain size however does not mean that modern humans are less intelligent. Human brains have evolved to work more efficiently and utilize less energy.

What I want to know, exactly is how they reached this conclusion in the first place. A shrinking brain couldn't possibly be a sign of decreased capacity, could it?

It is not worrying, bigger body needs bigger brain to empower it, our brain didnt get proportionally smaller, also there is no correlation between brain size and intelligence, actually there is minimal correlation which represent diminished intelligence of people with smaller heads but this smallness is due to abusive drinking or crack using during the pregnancy, or in some cases the umbilical cord get entangled and the fetus doesnt get enough nutrition and it ends up with smaller head, after that it cant compensate this period.
If person have naturally smaller head due to very fine bones and gracile structure this doesnt indicate reduced intelligence!
So at general we get smaller and more gracile, and the brain get smaller as part of the proportions humans have.
Stupid scientist have implied this kind of thinking our brain shrink so we get more stupid - Bull Shit!

"Stupid scientist have implied this kind of thinking our brain shrink so we get more stupid"

Try reading the article, in your case get an adult to read it with you, the big words (the ones you have to pronounce phonetically) seem to be stretching your comprehension skills.

"This reduction in brain size however does not mean that modern humans are less intelligent."

If you dont agree then argue with me, what kind or rats just rate and then go?
...
Deesky I dont give a f. about your ratings, but if you think I am wrong somewhere just post your view, otherwise you are just stupid rat, so ratings from people like you dont bother me really.

Get use to it, man. Like anywhere else on the internet, this place is over-run with trolls. The handful of worthwhile people usually make it, well, worthwhile though.

Interesting that this article doesn't seem to address brain-to-body ratio. Some quick math (average body weight divided by brain volume) tells us the brain is increasing in size in relation to our body.

"Stupid scientist have implied this kind of thinking our brain shrink so we get more stupid"

Try reading the article, in your case get an adult to read it with you, the big words (the ones you have to pronounce phonetically) seem to be stretching your comprehension skills.

"This reduction in brain size however does not mean that modern humans are less intelligent."

English is not my first language so chill out, and second I dont say that this article say we get more stupid, I am reading this about our shrinking brain over and over again, and in some cases they say that we get more stupid, in other they say something like this:
"This reduction in brain size however does not mean that modern humans are less intelligent. Human brains have evolved to work more efficiently and utilize less energy."
Which again is pure stupid!
In many cases they dont take to the account the body mass, in other like this one they mentioned it but they divide the two things.

They explain the reduction of the body and the brain as they are not connected!?
Pseudo scientist thats what they are, and when they talk stupid things people should see it and to tell them they are stupid, they get paid for this shits , is this right how do you think?
And I am not the troll, if you think what I say is so stupid or not correct well, ok I am listening to your more smart version, what exactly you think about the topic?

I may use some big words here but it is because stupidity drives me crazy, we rely on scientists to educate us, and to answer some questions here, did they manage to do it yes most of the times, but some scientists are stupid and some degrees they have dont get them the power to talk what they want just like that, it is their job to know and to think and in this case they failed a lot..... they show big ignorance here if you dont see it you are just too simple to see it.

It is not worrying, bigger body needs bigger brain to empower it,...

By that logic a brontosaurus would have a brain roughly the side of a Cadillac, not the size of walnut which fossil records show.

What is your problem dude, there is no controversy, no big discovery, just a few interesting quips about our evolution over the relatively short time span of ~100k years.

No need for wild rants and speculation.

Brontosaurus is really far from the humans man, we are mammals, take a look at the mammals, do you know how big is the brain of an elephant? It is 5 kg. Take a look at the dogs, their head size vary a lot, do the dogs with the most big heads are smarter?
Not at all, No 1 is the border collie, No 2 is the Poodle, these dogs dont have big heads.Their head size (and brain size) correlate with their body size just like the humans.
Actually the change is even more resent, more like 10k years, this just proves that not our proportions change but our size, as I said you may find easily people morphologically close to the people which were living back then. What I actually dont like is all this speculations, yes I may overreact, but this is again the next article which dont explain the things simple as they are but drives wild and false conclusions, I have read a lot worse ones about the topic and all the conclusions are made by scientists try to play smart and not saying the boring truth.

Why of why do Americans insist upon using such stupidities as "gotten" when got is not only correct but also totally adequate and then there is "anyways" instead of anyway which again is correct and totally adequate and even worse is got "off of" you never get off of, you simply get off. Once again the simple got off or any other combination is correct and totally adequate.
Why then do Americans feel this obsessive need to add to perfectly adequate words and end by sounding illiterate?

Why do they use Imperial for weight and Metric for volume? Is this a standard in scientific articles in the USA or are the authors just incapable of picking one system of measurement?

Just asking...

@Djincs Perhaps brain to body size has something to do with energy use. So far, I think that the only possibility they've excluded is the one, in which, we might be becoming less intelligent as a species. I think that's overly optimistic. But the brain has been shown to be highly plastic and capable of rapid growth. Perhaps, in the past, this rapid growth was due to hunter-gathering and living off the land? Maybe they should compare the brains of hunter-gatherers to farmers to test their conclusion.

I like Sinister1811's idea of comparing the brains of hunter-gatherers to others.

But I would certainly have appreciated the article more if it had hard nutritional science. For example, "Northern Europeans have lighter skin than native peoples who live even farther North because Northern Europeans had to evolve depigmentation to get sufficient vitamin D from scarce sunlight when they switched to agriculture and began eating less meat (meat is a source of vitamin D - grains are not)" tells us something we probably didn't know about what goes on in the body from our food. Okay, so it talks about niacin; and there is objective evidence (PET imaging) that smart people's brains tend to use energy more efficiently.

I was just reading about the Paleo/primal diet; its no good. It is based on eating lots and lots of meat and fat. Even though they traditionally ate a lot of calcium from soft-boned fish Inuits traditionally have a high rate of hip fractures because the intestines break down meat into individual amino acids before they are absorbed into the bloodstream. Absorbing too much amino acids at once acidifies the blood; the body responds to acidosis by releasing alkaline minerals from the bones to bring the venous pH closer to normal.

Some fats (especially the polyunsaturated fat DHA found in fish and algae) are good for the brain, but rats fed a diet high in the saturated animal fat lard consistently learn slower. The Paleo dieters do have one thing right though: grass-fed cows produce healthier meat.

the changes in the brain are much slower than changes like depigmentation(you can find white varieties of all sort of domesticated animals and flowers), also changes in how big you are can happen really fast(also given the fact all the different breeds of domesticated animals), all the thinking are we more stupid now or not is not correct, as I mentioned twice before you can find big unreduced humans even now with bigger heads and really big and broad bones, and they are not smarter, human intelligence have many aspects and is really hard to be estimated IMO, but a good game which represent it is the chess playing- it involve really unique human trait of the human intelligence, you can see there that the best players dont have bigger heads than the normal. All tests made in this direction shows no correlation, maybe subtle one but above somewhere I explained the reasons for that.

And I really dont think diet itself have anything to do with intelligence, nutrition yes but the diet itself no, hunters are more likely to starve so this is not good for the brain, also the brain works only with glucose(if there is no one it may work with fat derivatives but this is not beneficial), so having carbs in the diet is good for the body, human metabolism seems to adopted the new diet pretty fast and good.
Agriculture also includes milk and meet consumption so I really think people having agriculture were better fed, the fact our body shrunk is something that should be explained not by the diet, at that time lots of things changed, the way of living, the social structure also , the weapons, so all that should be accounted not only the diet.

Actually all this thinking about the diet is pure stupid, take a look at the hunters now days, which never had agriculture, they are the smallest people now but they live in hot areas, actually the climate determines much more how big you are(how big is your head/brain), northern you live bigger you are to keep the heat more efficient just like all the mammalian species, if they talk about Europe , this reduction represent not only some kind of evolution to smaller people, but even replacing of the old europeans- the big one paleolitic people with the agriculturists which came in Europe from south and were much smaller, so the reduction happened much faster

Neurotransmitters are made primarily from amino acids (from protein).

Anyway, bigger heads doesn't necessarily mean more neurons.

Lol so much people disagree but no one have the balls to say why? This site has become a rat sanctuary!

I was just reading about the Paleo/primal diet; its no good.

There's more to a Paleo-diet than meat and fat, in fact it's mainly supposed to be uncooked veggies and fruits/nuts, eggs and fish. I think most people who subscribe to it also (or are supposed to, at least) subscribe to the Paleo-exercise routine too, barefoot running, body-weight resistance workouts, climbing, jumping, etc. as well as mid-day napping. But just like any fad diet, it's not right for everyone (or even most?). However, some people legitimately benefit from it. Different metabolisms and even ethnicities have diets that are ideal for their body chemistry and ethno-biology. To say that it's no good across the board isn't really fair.

Emsguared, what is a good source of information about the Paleo diet?

This research is fine, but isn't the conclusion contraindicated by the Australian Aborigines and Kalahari Bushmen? Neither developed agriculture (well Victorian Aborigines might have, but none on the rest of the Australian continent) and neither are larger physically or in cranium size.
You might excuse the Kalahari Bushmen for being pygmies because the Kalahari desert is not exactly rich in food sources, but the Australian Aborigine lived in a variety of environments and ecosystems, some of which were very rich indeed, as hunter gatherers.

As they have been isolated for more than 10,000 years, some estimates put them as 70,000 years, then they should still have the characteristics reported reported and so they should be huge and with larger craniums

Human size as the size of all living creature is determined by two factors, first is the limitation of the resources which tend to make the creatures smaller, the second factor is the requirement how big you should be in order to survive, so do you eat meat or plants doesnt matter, what matter is how big you should be in order to get food, or just to survive another factor in the environment which pushes your growth in to some extend.
So people here and the scientists just show lots of "knowledge", but they lack thinking capability and logic!
So if you hunt small pray, or you have good weapons to kill big one you dont need big size, if you are agriculturist you dont need big size.
If you hunt big game and you are in the stone age you need big size(living in the north contribute too because of the cold), thats why people back then were bigger, with bigger heads and more brain, but not smarter.
It is as simple as that.

lol...

To smell stuff ...ect all affects the size of the brain; which has nothing to do with intel. And as mentioned by other/s farming gave humas more reliable calories to support the energy consuption of the brain.

One sided articals like this... u just gotta chuckle.

@ILIAD
You are right man, I think the same, but the majority of the people here are too stupid to see the epic fails of some "scientists"....
If agriculture required big size, then the people would have been bigger, but it doesnt, so we got smaller. Nature wont keep something you dont need.
And all this mistery why our brain get smaller....pure stupidity!

Emsguared, what is a good source of information about the Paleo diet?

I'm not too versed in the community, I just looked into it at one point when I was unemployed awhile ago.

However, I've seen http://cavemanforum.com/ reputed as being pretty decent for community, I'm sure people there could help you alot more.

There's all kinds of blogs from people who practice the whole thing or just various aspects of it. Just google things like "caveman diet", "paleo lifestyle", "paleo diet", and if just a particular sub-sect interests you, there's specialist communities for that too, barefoot running, especially.

Have fun exploring it, it's actually pretty interesting!

Ok this article contradicts itself several times

And was obviously not proof-read...

"Within the last 10 years, the average human size has changed to a weight between 154 and 176 pounds and a brain size of 1,350 cubic centimeters."

Which would be very worrying if true! ;-)

Maybe is true! Just look at the people we elect to govern us... not to mention our failed economic fiat system... LOL

Are we supposed to take this article seriously? You must be kidding. Right?

Predators need a larger brain to track prey and remember thier area but a grazing animal only has to find the next clump of grass. In a farming village a person who might get lost in the forest and who cannot run very fast has an equal chance of passing on his genes as someone of higher ability. Africa is a good example ,they have the watutsi (excuse my spelling) that are over 6 feet tall to suvive the hot climate and then the pigmes around 3 feet tall so they can travel in the thick undergrowth and they both have a common ancester. I would think the method of gathering food is a bigger factor than diet in determining evolutionary changes (natural selection)in a species.

The selection pressure is likely to be more along the lines of humans having improved technology, including the Australian aborigines, who had fish traps, etc, leading to social and cultural structures that made a form of internal domestication possible. The powerful in this scenario would tend to eliminate the more independent (smarter and stronger) and keep the less difficult (dumber and weaker). Much as we have done with domesticated animals. We have domesticated ourselves, and made our species physically less robust and intellectually poorer. Idiocracy on its way.

@ unknownorgin

I see your point and it is true to some extend, but farming even taken the fact that doesnt include orientation, dont suggest you need less brain power, quite the opposite, it is not like the animals to go and to eat it, but you should plant it, protect it, also farming brings more people together and things get more complicated in a big society, you should be much more aware about the games people play, this is true for all mammalian species, that the bigger the social structure is, bigger brain you need(not always of course), about the tallness of some Africans I think it is due more to sexual selection(tallness is considered sexy for lots of african tribes), or just long legs are better at walking great distances, it has nothing to do with surviving hot climate really.
But yes what I am also try to explain is that indeed the way you get food is much more important than the type of food you get.

@ brainlennon
I dont think that in farming society or in our society stupid people have bigger chance to survive really.
But there is a grain of truth in this, farming society have changed the thing significantly, people started to own much more things, so who you are in the society depends much more to what you have and not who you are, in hunting societies people have more equal start, and your "DNA" matters much more, and not how much cows you have or how much land you have.

"Idiocracy on its way."

The Marching Morons
Galaxy Science Fiction April 1951
John Barlow, a man from the past put into suspended animation by a freak accident involving a dental drill and anesthesia. He is revived in a dystopic future where the dysgenic breeding of humans has, in combination with intelligent people not having many children, overwhelmingly populated the world with morons. An elite few non-idiots must work slavishly to keep the world productive.

The audiobook available at
http://www.sffaud...p?s=C.M. Kornbluth

Rgds
James

"Idiocracy on its way."

The Marching Morons
Galaxy Science Fiction April 1951
John Barlow, a man from the past put into suspended animation by a freak accident involving a dental drill and anesthesia. He is revived in a dystopic future where the dysgenic breeding of humans has, in combination with intelligent people not having many children, overwhelmingly populated the world with morons. An elite few non-idiots must work slavishly to keep the world productive.

The audiobook available at
http://www.sffaud...ornbluth

Rgds
James

We are DEVO.

Smaller is good. Small people use less resources. Large people use more resources. You don't have to be big to be smart or do things. In other words, farming has done us a favor.

Who has been studying human fossil evidence for 200,000 years? The article claims humans have been around much longer than what is true. Hopefully my tax dollars are not going to Britain to fund this nonsense. Wow, reading the comments would lead me to think we really did evolve from apes!
I didn't know that cameras were invented that far back to have taken that picture. So if our brains are getting smaller, how does that jive with evolution? So random chance is making our brain more efficient, thus smaller. Can I get
random chance to make my cell phone smaller and more intelligent?

Give me a break.

Ok this article contradicts itself several times

And was obviously not proof-read...

"Within the last 10 years, the average human size has changed to a weight between 154 and 176 pounds and a brain size of 1,350 cubic centimeters."

Which would be very worrying if true! ;-)

the weight definitely makes sense. majority of the world population are starved and are weighing less than this.

Thanks for a great article. It seems that choice of words and the way that evolutionary biologists explain changes, can be confusing for us lay folks. The mechanisms of cause and effect are not as clear when looking back so far and with so many variables, and so we should read articles and language in the context of general trends and tendencies, rather than mechanistic processes. Like Rhetorical reasoning as apposed to logical reasoning.

This approach keeps the conversation going, and the information flowing, as apposed to no-one ever publishing an article since we are never in a position to have all the facts.

Thanks to the contributors of information.

This is misleading. Brain size is only a useful indicator of a species intelligence in relation to body size. Using the figures from this article, the median paleolithic body mass was 182 lbs, and modern median body mass is 165 lbs. The ratio of these two numbers is 1.103

1,350 cc x 1.103 = 1,489 cc, which is well within the margin of error for the 1,500 cc cranial capacity figure for paleolithic humans.

In other words, the decrease in body mass can easily explain the decrease in cranial capacity, and does not imply a decrease in intelligence.

Actually estimating is good idea.
The mean of 176 and 188 is 182 in kg this is 82,7/1,5 = 55
the mean of 154 and 176 is 165 in kg this is 75/1,35 = 55
so the ratio body mass/brain size doesnt change at all.

Silly scientists, go to plant potatoes.

If you compare the achievements of hunter gatherers vs the achievements of agriculturists , the latter outshine the former in all fields.

The Aztecs, Sumerians, Indus Valley, and countless other "agricultural" civilizations prove that settling down tends to exponentially increase intelligence.

Agriculture may accelerate culture(especially in places like near big rivers where there are great gathering of people, the food is abundant and some people can start to develop and do other things like pottery and stuff, and the need for writing when you have lots of people who have to pay taxes and to have some records is inevitable), but genetically there is not difference in the biological capacity of the agriculturists and hunters, after all, agriculture is not that old evolutionary speaking and the agriculturists were hunters before that.

Silly scientists, go to plant potatoes.

I think you're taking my argument out of context. I meant it as a caveat, not a refutation of science.

Agriculture may accelerate culture... but genetically there is not difference in the biological capacity of the agriculturists and hunters, after all, agriculture is not that old evolutionary speaking and the agriculturists were hunters before that.

Djincss is right here. 10,000 years of agriculture and 5,000 years (give or take) of urbanism is a drop in the bucket on evolutionary timescales. The changes in civilization that occurred over these time periods are cultural, not biological. Aside from body mass reduction due to decreased micronutrients, we're no biologically different than the homo sapiens that came out of Africa in the pleistocene. Now, there are environmental factors that influence IQ, but other than that, "intelligence" might not be the right word.

I am talking only about the scientists in the article, I wont offend anyone here despite how wrong some opinion may look, we are ordinary people which job is far from science in most cases.
What annoys me is when people which job is science talk shits and make silly statement(based on pseudo logic) showing their enormous ignorance.

I am talking only about the scientists in the article, I wont offend anyone here despite how wrong some opinion may look, we are ordinary people which job is far from science in most cases.
What annoys me is when people which job is science talk shits and make silly statement(based on pseudo logic) showing their enormous ignorance.

-Djincss

The words you're looking for are "whose job" not "which job". Also, you need a period after "job is science". You need to capitalize "Talk". The plural in the following "sentance" should be after talk and not "sh*t". Also, "statement" should be made plural. If one is going to be high and mighty, one should, in the least, attempt to sound as educated as the group one is trying to critique. Otherwise, no person in their sane mind will read what you post. Instead, they will see the first post, skip to your last post, and rate your grammar skills, accordingly, on all posts(as I have done).

Honestly I dont care what the rates are, my English is not perfect and if you think I am stupid just because of that...well think what you want.
Also I think the purpose of comments here are for sharing opinions, if you can get what I am talking about, this is enough for me.
But again thanks for sharing your opinion I dont judge the criteria for the rate or the rate itself , I just dont think that the right thing is to rate 1, and not to share your view as the majority of people do here, I will be actually glad if the low rate just represent my grammar.
And I dont want to be mighty, I am human and I have my emotions, also this is normal way of talking where I am from, so it may be just cultural difference if you find it so outrageous.

@OutermostSoup

So you have joined yesterday and have made only this post....
what kind of troll rat you are, it is clear this is muppet account. Not only you are rat but stupid rat as everyone here can clearly see. GTFO and dont waste my time.
I just want a clear and meaningful discussion here and to exchange some thoughts but clearly this site is full of rats and stupid people.

No one in his right mind believes this utter nonsense. Evolutionary science has become so completely blind and is devoid of the most basic ability to self-reflect. Science really is in a fundamental crisis of credibility.

Lower aggregate demand on breeding.
The genes of the hunter/gatherers that were passed on were the brightest, fastest, strongest, virulent etc. With farming and division of labor that came from larger sustainable communities, came excessive qualities at the expense of the aggregate whole. Now we even have fertility treatments so you don't even have to have an intact ability to breed. Legally enforced monogamy has also pushed for nearly everyone's genes to get passed on with little evolutionary pressure on merit.
The weakest herds of any wild animal are those that are subject to the least predation and competition for food. That is why invasive species are mostly a problem of animals from larger bio areas being introduced to smaller ones. Little competition in small island ecosystems left them only having to have minimal defenses against predation and minimal ability to compete for food.
Mega-fauna resulted from predation pressure but no food pressure and died off when that came about.

Not enough facts , needs a global selection of subjects ,all things need to be considered equally then let the math begin! What else happened at that time frame ? Younger dryas for one, end or the ice age, the begging of the 6th ELE. Why did people need to farm ? what was the cause and effect?