I read that the human brain has not evolved in 100 000 years and that's why there are no genes for intelligence.
closed as unclear what you're asking by David, canadianer, Bryan Krause♦, kmm, another 'Homo sapien' Aug 3 '17 at 15:45
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Here are the two claims you make
human brain has not evolved in 100 000 years
there are no genes for intelligence.
there are no genes for intelligence. is unclear though (see below) but if rephrased in the most intuitive correct way, then the claim is wrong!
Are there genes for intelligence?
[..] there are no genes for intelligence.
The claim there are no genes for intelligence is unclear. Does that mean there is no genetic variance in the human population for intelligence? To understand why the claim "gene for something" makes no sense, please have a look at this post
Make sure to read this post..... Done? Now you understand why the concept of heritability is key. So let's rephrase the question so that it makes sense and can be answered
Is Intelligence heritable?
Well, the issue here is to define the term 'intelligence' in a way that is non-arbitrary and yet match our intuition of what we like to call intelligent. A number of studies have investigated the heritability of intelligence, often using different definitions / metrics for intelligence.
All these studies agree on one point. Yes, intelligence is heritable! How heritable it is varies a lot from one study to another (because those studies vary in the population studied and in the definition of intelligence). See the wikipedia article on Heritability of IQ for more layman information.
Has the human brain evolved in the past 100 000 years?
First you need to understand how evolution is defined. Here is a commonly used definition
Evolution is a change of allele frequency through time in a population
Have a look at the post What is meant by
individuals do not evolve, populations do? to understand what this definition mean.
Well... first. Everything evolve. You can't stop evolution from happening on any phenotypic trait or on any genomic region. So, of course it evolves. But let's not stop there.
There is still one issue with this question. The saying brain characteristics rather vague. But I'll deal with it as I can.
Is the brain still evolving - phenotypic evidence
Spoting changes in brain structure through time is not easy, as brains don't preserve well. Over such a short period of time (100,000 years) it will be even harder to detect much difference on gross metrics we can use such as cranial cavity.
We can compare the volumes of cranial cavity. Neanderthals interbred with humans (see this loosely related post) with Homo sapiens and Nanderthals had a cranial cavity that is bigger than Homo sapiens, so this gene flow would very likely affect H. sapiens cranial cavity.
Is the brain still evolving - genetic evidence
Consider for example Evans et al. 2005 showing that the allele coding for micro-encephaly at the gene MCPH1 is currently increasing in frequency in the human population.
Is the brain still evolving - current selection pressures
You should have a look at the post Is intelligence declining due to the lack of selection pressure? and eventually on the wikipedia article for the Flynn Effect.
Every part of the human genome is constantly evolving - but at a VERY slow rate. Therefore there are only a few changes from the last 100k years (This article describes this quite well).
Intelligence is a very complex characteristic, which is therefore influenced by many different genes. Most of these influences are only minor, so that scientists are arguing whether the influence is real or not (pro, uncertain, contra). Additionally there are a lot of genes that are just necessary for the brain to function the way it does - you could argue that all of these are 'genes for intelligence, since without them we would not be intelligent.
I'm curious to where you read that b/c its simply not true. Remember that evolution is driven by selection pressures. Also known as evolutionary pressures, they drive a reason to evolve. The stronger the pressure the faster evolution takes place. An easy way to spot this pressure is by looking at the range in ability, skill or adaptation of a trait. The larger the range the stronger the pressure.
With that in mind, can you think of any selection pressures that the human brain might had to face over half your given time, lets say the past 50,000 years?
The human brain has had to adapt to entirely new environments in that time frame.
Within that time-frame is all of recorded history. How about the adaptation to formal education? That might be one. Also during this time think of the explosion in languages. Consider how different we all are in our ability to be educated and to pick up languages. Or how some of us can cognitively operate effectively with wildly different amounts of sleep debt or calorie intake.
Also there are many genes that influence intelligence since intelligence is multifaceted and can be expressed in many ways. You also need to remember that these pressures can influence how genes are turned on or off. This is known as epigenetics. You might have a gene but your cells could simply not use it.
There have been theories of autism being a result of an evolutionary pressure.
With all of this in mind the last thing you need to remember is that the human brain is evolving in other ways than simply via its genes or their expression. The human brain exists in a space shared by other human brains and we have the ability of sharing our ideas with others. This allows for groups of people to share a selection pressure and thus evolve as a group.
Do you know what this is called? I know you know.
Culture. In many ways human evolution has moved on from the biological to the cultural space. And I find that quite fascinating.