<p>Up until the 70s and 80s, there were decades of hot debate about whether some phenotype such as brain structure or some behavior were caused by genes or by environment. Wikipedia has a decent summary of the history and content of that debate, and I've linked to the section on estimating the relative contribution of genes vs. environment: <a href="https://en.wikipedia.org/wiki/Nature_versus_nurture#Heritability_estimates" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Nature_versus_nurture#Heritability_estimates</a></p>

<p>The current consensus is that the #1 question isn't very meaningful. Genes and environment are both 100% necessary conditions for a brain to develop. Yes, the similarity between brains (and between species) show that a lot of the structure is conserved, and much of that design depends on genes. But those genes wouldn't develop into a brain without very specific environmental conditions.</p>

<p>There are three quite distinct questions under #2. Cells and regions differentiate in the body; brain plasticity isn't 100%. Some structure is conserved. Consider that "modularity", one type of which is that different areas of the brain do distinct operations, is at least partially false. The brain is not at all like a computer with a motherboard with distinct components. It might help to consider how you would answer your question for why people's thumbs don't look like their other fingers. What prevents a thumb from developing into a finger? Are the functions of a thumb determined by genetics? This might help you to zero in on the specific processes of the brain that are the mechanisms that explain how genes and environments interact to produce phenotypes.</p>

CC BY-SA 4.0
2019-05-21T06:57:12.940Z
But how much of how the brain functions can be attributed to genetics? Are there a few papers that I can read perhaps?
Chandrahas
CC BY-SA 4.0
2019-05-21T07:04:25.113Z
As an example, I know that certain regions in the brain house predominantly excitatory neurons (VTA's dopamine neurons etc) while a few other nuclei house inhibitory ones. Is the excitatory or inhibitory character of neurons in brain regions determined by plasticity(similar to how Artificial Neural Networks "learn" to have negative or positive weights to match data sets) or is the said character determined during cell division itself.
Chandrahas
CC BY-SA 4.0
2019-05-21T08:08:32.470Z
I'm not an expert at that level of mechanism, but my guess is that it's not so simply as one or the other. The final cell morphology and activity are the function of all the inputs over time, not just the beginning or ending ones.
Cameron Brick
CC BY-SA 4.0
2019-05-20T10:14:15.880Z
2019-05-20T10:14:15.880Z
Cameron Brick
<p>As a result of my growing interest in neuroscience, I have begun to try and understand the functioning of the brain. However, I am always confronted by the  following questions: </p>

<ol>
<li><p>The brain is a highly specialized organ with innumerable nuclei and pathways, and yet the brain of one individual is surprisingly similar to that of another. Hence, it must be the case that the structure of the brain must, in part, be determined by our genes. If this assessment is correct, how much is our brain structure dependent on our genes?</p></li>
<li><p>Now consider the case of a newborn and suppose his/her brain structure has been established somehow. As he/she grows, the brain starts taking sensory input and learns to process it better through neuroplasticity. If so, then why does everyone's, say amygdala only process fear, anxiety, etc. What prevents it from maintaining autonomous functions? Are the functions of different parts also determined by our genetics? (Is neuroplasticity the only force dictating learning?)</p></li>
</ol>

<p>In other words, why are all human brains so similar in brain structure, specialization of their parts and functioning?</p>

<p>Thank you</p>

CC BY-SA 4.0
2019-05-17T15:29:15.857Z
You might want to take a look at one of my questions https://psychology.stackexchange.com/questions/10070/how-similar-are-the-brains-of-twins
StrongBad
CC BY-SA 4.0
2019-05-20T10:42:13.863Z
The brains of animals in every species, not only human, are similar in structure and specializations to the brains of other members of that species. This fact includes not only mammalians, but also reptiles, birds, and even insects, which have quite different brain structures and specializations from those of human brains. So, genes in each species must play an important role in controlling brain development of that species. Yet, environmental factors are important too. Please see this [ref](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/) for more discussion.
user287279
CC BY-SA 4.0
2019-06-19T13:44:20.863Z
Also closely related: https://psychology.stackexchange.com/q/10794/7001
Arnon Weinberg
CC BY-SA 4.0
2019-06-19T16:00:44.587Z
Possible duplicate of [How does it come about that specific areas of the brain are associated with specific functions?](https://psychology.stackexchange.com/questions/10794/how-does-it-come-about-that-specific-areas-of-the-brain-are-associated-with-spec)
Bryan Krause
<learning><brain-development>
why are all human brains so similar in brain structure, specialization of their parts and functioning?
Chandrahas
# why are all human brains so similar in brain structure, specialization of their parts and functioning?

(Asked by: username_0 on 2019-05-17)

As a result of my growing interest in neuroscience, I have begun to try and understand the functioning of the brain. However, I am always confronted by the following questions:

1. The brain is a highly specialized organ with innumerable nuclei and pathways, and yet the brain of one individual is surprisingly similar to that of another. Hence, it must be the case that the structure of the brain must, in part, be determined by our genes. If this assessment is correct, how much is our brain structure dependent on our genes?
2. Now consider the case of a newborn and suppose his/her brain structure has been established somehow. As he/she grows, the brain starts taking sensory input and learns to process it better through neuroplasticity. If so, then why does everyone's, say amygdala only process fear, anxiety, etc. What prevents it from maintaining autonomous functions? Are the functions of different parts also determined by our genetics? (Is neuroplasticity the only force dictating learning?)

In other words, why are all human brains so similar in brain structure, specialization of their parts and functioning?

Thank you

**Tags:** learning, brain-development

> **Comments:**
> **username_1**: You might want to take a look at one of my questions https://psychology.stackexchange.com/questions/10070/how-similar-are-the-brains-of-twins  
> **username_2**: The brains of animals in every species, not only human, are similar in structure and specializations to the brains of other members of that species. This fact includes not only mammalians, but also reptiles, birds, and even insects, which have quite different brain structures and specializations from those of human brains. So, genes in each species must play an important role in controlling brain development of that species. Yet, environmental factors are important too. Please see this [ref](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/) for more discussion.  
> **username_3**: Also closely related: https://psychology.stackexchange.com/q/10794/7001  
> **username_4**: Possible duplicate of [How does it come about that specific areas of the brain are associated with specific functions?](https://psychology.stackexchange.com/questions/10794/how-does-it-come-about-that-specific-areas-of-the-brain-are-associated-with-spec)  

---

## 1 answers

### Answer by username_5 on 2019-05-20. Score: 1

Up until the 70s and 80s, there were decades of hot debate about whether some phenotype such as brain structure or some behavior were caused by genes or by environment. Wikipedia has a decent summary of the history and content of that debate, and I've linked to the section on estimating the relative contribution of genes vs. environment: <https://en.wikipedia.org/wiki/Nature_versus_nurture#Heritability_estimates>

The current consensus is that the #1 question isn't very meaningful. Genes and environment are both 100% necessary conditions for a brain to develop. Yes, the similarity between brains (and between species) show that a lot of the structure is conserved, and much of that design depends on genes. But those genes wouldn't develop into a brain without very specific environmental conditions.

There are three quite distinct questions under #2. Cells and regions differentiate in the body; brain plasticity isn't 100%. Some structure is conserved. Consider that "modularity", one type of which is that different areas of the brain do distinct operations, is at least partially false. The brain is not at all like a computer with a motherboard with distinct components. It might help to consider how you would answer your question for why people's thumbs don't look like their other fingers. What prevents a thumb from developing into a finger? Are the functions of a thumb determined by genetics? This might help you to zero in on the specific processes of the brain that are the mechanisms that explain how genes and environments interact to produce phenotypes.

> **Comments:**
> **username_0**: But how much of how the brain functions can be attributed to genetics? Are there a few papers that I can read perhaps?  
> **username_0**: As an example, I know that certain regions in the brain house predominantly excitatory neurons (VTA's dopamine neurons etc) while a few other nuclei house inhibitory ones. Is the excitatory or inhibitory character of neurons in brain regions determined by plasticity(similar to how Artificial Neural Networks "learn" to have negative or positive weights to match data sets) or is the said character determined during cell division itself.  
> **username_5**: I'm not an expert at that level of mechanism, but my guess is that it's not so simply as one or the other. The final cell morphology and activity are the function of all the inputs over time, not just the beginning or ending ones.  

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