High rates of autism and other neurodevelopmental disorders may be due to how humans evolved in the past, new research has suggested.
Increases in diagnoses have been increasing for decades, with one in 36 children in the UK believed to have Autism Spectrum Disorder.
Globally, the World Health Organisation[1] (WHO) estimates that around one in 100 children have autism.
Whilst there have been a number of factors theorised to be behind the increase in cases, with President Trump this week blaming Tylenol use during pregnancy[2], experts remain undecided as to whether the increase is also due to overdiagnosis or whether more children have the condition.
But now US researchers say that natural selection could have given rise to autism-associated genes, with behaviours associated with the disorder generally involving cognitive traits that are unique to humans.
Writing in the journal Molecular Biology and Evolution[3], experts at Stanford University discovered that the most abundant type of outer-layer brain neurons—called L2/3 IT neurons—evolved exceptionally quickly in humans compared to other mammals.
This rapid evolution involved a marked downregulation in genes linked with autism and schizophrenia, supporting the hypothesis that lower expression of autism-linked genes in humans increases the risk of autism.
According to the researchers, this accelerated evolution saw dramatic changes in autism-associated genes, which was likely driven by natural selection—a mechanism of evolution by which a species changes over time in response to changes in the environment, or competition between organisms.
Whilst the exact cause of autism remains unclear, US researchers believe that its prevalence may be linked to human brain evolution (stock image)
However, they added that the reason as to why this change benefited humans remains unclear.
One possible reason for this is that the rapid evolution of these specific genes could have slowed down postnatal brain development, increasing the capacity for language and more complex thinking patterns.
Alexander Starr, an expert in neurodevelopmental disorders and human evolution and study lead author said: ‘Our results suggest that some of the same genetic changes that make the human brain so unique also made humans more neurodiverse.’
The landmark research comes as Trump caused shockwaves last week as he claimed that taking paracetamol during pregnancy was fuelling a spiraling autism ‘crisis’. [4]
International scientists immediately dismissed his comments as ‘fear-mongering’, with ‘no robust evidence’ to support the claim.
However, others say while it remains unclear whether paracetamol causes autism—a condition which makes it difficult for people to understand social cues and express themselves—something is clearly driving the surge in cases with one in 100 now affected.
In an announcement on 22 September, Mr Trump told reporters that taking paracetamol was simply ‘not good’, declaring: ‘All pregnant women should talk to their doctors about limiting the use of this medication while pregnant.’
He later doubled down: ‘Fight like hell not to take it.’
Trump’s remarks which were later echoed by Nigel Farage sparked cross-party criticism with Conservative Party leader Kemi Badenoch branding them ‘irresponsible conspiracy-theory nonsense’, while Health Secretary Wes Streeting labelled Mr Farage a ‘snake oil salesman’
A handful of well-publicised studies have suggested a possible link between maternal use of paracetamol and higher rates of autism or ADHD.
But the findings are inconsistent, and experts stress that any association remains based on very limited and conflicting evidence.
The most recent, published last month by researchers at Mount Sinai in New York and Harvard’s School of Public Health, urged women to take paracetamol in pregnancy only on the advice of a doctor—though the authors acknowledged the evidence was not conclusive.
They urged mothers-to-be to use paracetamol sparingly, taking only the lowest effective dose for the shortest possible time.
But they stressed their results did not prove the drug directly causes autism or other neurodevelopmental disorders.
Instead, they said the association was consistent enough to warrant further investigation.
Health Secretary Wes Streeting also dismissed[5] the remarks.
‘Don’t pay any attention whatsoever to what Donald Trump says about medicine,’ he said.
‘In fact, don’t even take my word for it as a politician—listen to British doctors, British scientists, the NHS. It’s really important, at a time when there is scepticism, to follow medical science.’
In England, the number of children seeking help for suspected autism has spiralled to an all-time high in Covid’s wake.
According to latest NHS figures, almost 130,000 under 18s in England were still awaiting an assessment in December 2024—a six-fold increase on the 20,000 logged in December 2019.
Experts have long warned that young people are facing an ‘invisible crisis’, with a system that has repeatedly failed to keep pace with rising demand.
Autism is not a disease and people have it from the moment they are born, although it may not be spotted until childhood and sometimes much later.
It exists on a spectrum. Some people will be able to lead fully functioning lives with no additional help. Others may need full-time assistance.
References
- ^ World Health Organisation (www.dailymail.co.uk)
- ^ blaming Tylenol use during pregnancy (www.dailymail.co.uk)
- ^ Molecular Biology and Evolution (dx.doi.org)
- ^ fuelling a spiraling autism ‘crisis’. (www.dailymail.co.uk)
- ^ Wes Streeting also dismissed (www.dailymail.co.uk)
- ^ THE SIGNS AND SYMPTOMS OF AUTISM (www.dailymail.co.uk)