To what extent is intelligence genetically inherited?
A look at how the brain, our genes and the environment affect our cognitive abilities.
1
, Table of Contents
INTRODUCTION 3
A BACKGROUND TO INHERITANCE AND GENETICS 4
WHAT IS INTELLIGENCE? 4
THE BRAIN AND INTELLIGENCE 5
ARE LARGER BRAINS MORE INTELLIGENT? 5
WHICH PARTS OF THE BRAIN ARE IMPORTANT FOR INTELLIGENCE? 6
GREY MATTER AND INTELLIGENCE 6
WHITE MATTER AND INTELLIGENCE 6
CONCLUSIONS ON THE BRAIN 6
GENETICS 7
HOW COULD GENES DETERMINE INTELLIGENCE? 7
WHAT GENES? 7
GENES ON THE CELLS OF INTELLIGENCE 7
GENETICS AND TIME 8
CONCLUSIONS OF GENETIC STUDIES 8
USING TWIN AND ADOPTION TESTS TO EXPLORE GENE-ENVIRONMENT INTERACTIONS 8
IMPORTANCE OF TWIN TESTS 9
RESULTS OF TWIN TESTS 9
CRITICISMS OF TWIN TESTS 10
CONCLUSION 10
GLOSSARY 10
APPENDIX 11
REFERENCES: 12
BIBLIOGRAPHY 13
2
, “It takes something more than intelligence to act intelligently”
(Dostoyevsky, 1866)
Introduction
The argument of whether intelligence is inherited or affected by environmental factors has been the
subject of debate for many years. Historically, scientists believed that people were born with a
predetermined amount of intelligence because of their family. This is now known as genetics. As a result,
it was thought that there was nothing that could be done to raise a child's IQ or general intelligence. Yet,
more modern approaches view cognition as something that can be improved through environmental
intervention which can enhance an individual’s IQ. Using different perspectives, intelligence can be seen
as the sum of genetics and environmental factors due to each factor’s inability to be completely removed
from the other. If a child is born and lives with the same family with which they were born this means that
share both an environment and genetic traits – intertwining the two factors. Due to this, it can only be
questioned what proportion of the values established for genetics and the environment truly can be
segregated into separate factors, creating the question – of ‘to what extent is intelligence inherited’.
To this day the argument of whether we are products of our genes or environment sparks controversy
amongst scientists. Research done into cognitive abilities linked with intelligence in humans has been
ground-breaking in helping establish treatments and understanding of mental disabilities and diseases
which affect intellectual skills such as the gene linkage of the APOE-e4 gene with Alzheimer’s, where 40-
60% of Alzheimer’s patients have the gene (Liu CC, 2013). Linking genes to intelligence is also important
concerning education and helping decide which children required individualised attention when it comes
to special education needs such as Down’s Syndrome, Williams Syndrome and Fragile X Syndrome (C,
2012).
This essay explores the effects of genetics on intelligence. This will be done through an examination of
their effects on the brain and cells and how they play roles in determining intelligence, alongside how
genes change in impact over time. Other factors which affect intelligence will also be explored, using
research from twin tests, adoption, and genetic studies to answer the essay question.
Brief Summary of The Essay Structure
There is much to learn and explore about what intelligence is and how it is determined therefore my
essay will mainly focus on the two factors of genetics and the environment with any additional valuable
information also being outlined. The essay will begin with an introduction to the topic with a background
on inheritance and genetics, followed by an explanation of what intelligence is, its history and what the
definition will be in this essay. I will then explore the effects of the brain and its many features as I believe
that it is a key component in understanding the biological basis for intelligence due to its size and
elements. Both my genetics and environmental sections are split into many subsections each with
evidence to build up the argument. I will also use secondary evidence from twin tests and adoption
studies as well as key scientific theories which contribute to the essay.
3
A look at how the brain, our genes and the environment affect our cognitive abilities.
1
, Table of Contents
INTRODUCTION 3
A BACKGROUND TO INHERITANCE AND GENETICS 4
WHAT IS INTELLIGENCE? 4
THE BRAIN AND INTELLIGENCE 5
ARE LARGER BRAINS MORE INTELLIGENT? 5
WHICH PARTS OF THE BRAIN ARE IMPORTANT FOR INTELLIGENCE? 6
GREY MATTER AND INTELLIGENCE 6
WHITE MATTER AND INTELLIGENCE 6
CONCLUSIONS ON THE BRAIN 6
GENETICS 7
HOW COULD GENES DETERMINE INTELLIGENCE? 7
WHAT GENES? 7
GENES ON THE CELLS OF INTELLIGENCE 7
GENETICS AND TIME 8
CONCLUSIONS OF GENETIC STUDIES 8
USING TWIN AND ADOPTION TESTS TO EXPLORE GENE-ENVIRONMENT INTERACTIONS 8
IMPORTANCE OF TWIN TESTS 9
RESULTS OF TWIN TESTS 9
CRITICISMS OF TWIN TESTS 10
CONCLUSION 10
GLOSSARY 10
APPENDIX 11
REFERENCES: 12
BIBLIOGRAPHY 13
2
, “It takes something more than intelligence to act intelligently”
(Dostoyevsky, 1866)
Introduction
The argument of whether intelligence is inherited or affected by environmental factors has been the
subject of debate for many years. Historically, scientists believed that people were born with a
predetermined amount of intelligence because of their family. This is now known as genetics. As a result,
it was thought that there was nothing that could be done to raise a child's IQ or general intelligence. Yet,
more modern approaches view cognition as something that can be improved through environmental
intervention which can enhance an individual’s IQ. Using different perspectives, intelligence can be seen
as the sum of genetics and environmental factors due to each factor’s inability to be completely removed
from the other. If a child is born and lives with the same family with which they were born this means that
share both an environment and genetic traits – intertwining the two factors. Due to this, it can only be
questioned what proportion of the values established for genetics and the environment truly can be
segregated into separate factors, creating the question – of ‘to what extent is intelligence inherited’.
To this day the argument of whether we are products of our genes or environment sparks controversy
amongst scientists. Research done into cognitive abilities linked with intelligence in humans has been
ground-breaking in helping establish treatments and understanding of mental disabilities and diseases
which affect intellectual skills such as the gene linkage of the APOE-e4 gene with Alzheimer’s, where 40-
60% of Alzheimer’s patients have the gene (Liu CC, 2013). Linking genes to intelligence is also important
concerning education and helping decide which children required individualised attention when it comes
to special education needs such as Down’s Syndrome, Williams Syndrome and Fragile X Syndrome (C,
2012).
This essay explores the effects of genetics on intelligence. This will be done through an examination of
their effects on the brain and cells and how they play roles in determining intelligence, alongside how
genes change in impact over time. Other factors which affect intelligence will also be explored, using
research from twin tests, adoption, and genetic studies to answer the essay question.
Brief Summary of The Essay Structure
There is much to learn and explore about what intelligence is and how it is determined therefore my
essay will mainly focus on the two factors of genetics and the environment with any additional valuable
information also being outlined. The essay will begin with an introduction to the topic with a background
on inheritance and genetics, followed by an explanation of what intelligence is, its history and what the
definition will be in this essay. I will then explore the effects of the brain and its many features as I believe
that it is a key component in understanding the biological basis for intelligence due to its size and
elements. Both my genetics and environmental sections are split into many subsections each with
evidence to build up the argument. I will also use secondary evidence from twin tests and adoption
studies as well as key scientific theories which contribute to the essay.
3
