The teaching of creationism could "creep in" to schools under Wales' new curriculum, scientists have said.
A letter signed by 46 individuals and organisations, including Sir David Attenborough, asks the Welsh Government to explicitly ban the teaching of creationism as science.
Organised by campaign group Humanists UK, it also calls for primary school pupils to be taught about evolution.
The Welsh Government said it expects "all pupils will be taught evolution".
The new curriculum, due to be rolled out from September 2022, sets out six broad "areas of learning and experience" including science and technology.
A draft version published in April sets out "what matters" in each area and is meant to give teachers flexibility to decide on the details of how they cover them.
But scientists - including Richard Dawkins, Steve Jones and Alice Roberts - warned the changes could increase the possibility of teaching creationism as science.
"The new science and technology area of learning and experience doesn't explicitly prohibit presenting creationism and other pseudoscientific theories as evidence-based and evolution is only mentioned once (and only at secondary level at that)," the letter said.
"Pupils should be introduced to it early - certainly at primary level - as it underpins so much else.
"What's more, without an explicit ban on teaching creationism, intelligent design and other pseudoscientific theories as evidence-based, such teaching may begin to creep into the school curriculum, when it is vital children in Wales are not exposed to pseudoscientific doctrines masquerading as science".
Wales Humanists coordinator Kathy Riddick said she was not aware of "blatant teaching of creationism" within Welsh schools.
But she said the approach in the draft curriculum "could make it much easier for a school, such as a religious school, to openly teach creationism as science".
A Welsh Government spokesman said: "It is wholly incorrect to claim that evolution will only be introduced at 14 -16.
"We believe that providing children with an understanding of evolution at an early age will help lay foundations for a better understanding of wider scientific concepts later on."