Which came first: the chicken or the egg? Scientists think they’ve finally cracked it!
- A new study has found that the hen’s ancestor may not have laid eggs
- Scientists have long believed that this practice was crucial in evolution
- But a team of fallopian academics now believes amniotes gave birth to live young
It’s a question on everyone’s mind, from scientists to schoolchildren – and now scientists may just have an answer to this most baffling of evolutionary conundrums.
A study has now given free rein to a new theory about the chicken-and-egg issue after discovering that early ancestors of modern birds and reptiles may have given birth to live young instead of laying hard eggs.
In evolutionary terms, eggs were laid by the chicken’s distant dinosaur ancestors millions of years before the first chickens evolved.
This was thought to have solved the age-old question of whether the chicken or the egg came first.
But did it come before the chicken? A new study suggests it may not be so simple after all
But a new research project has now found that the chicken’s earliest reptilian ancestors, dating back millions of years before even the dinosaurs evolved, may not have laid eggs as previously thought.
Scientists have long believed that more than 300 million years ago, hard-shell egg-laying played a critical role in the early evolutionary success of the amniotes, a group of vertebrates that undergo embryonic or fetal development in an amnion, a protective membrane in the egg.
A new study of 51 fossil species and 29 living species that can be categorized as oviparous — laying hard or soft-shelled eggs — or viviparous — giving birth to live young — suggests otherwise.
Experts say that while the hard-shelled egg is often seen as one of evolution’s greatest innovations, this research implies that the embryo is retained longer – when the young are held by the mother for varying amounts of time – this particular group has of animals the ultimate protection.
Professor Michael Benton from the University of Bristol’s School of Earth Sciences said: ‘Before amniotes, the first tetrapods to develop limbs from fish fins were generally amphibious in habits.
‘They had to live in or near water to feed and reproduce, like modern amphibians such as frogs and salamanders.
‘When the amniotes appeared on the scene 320 million years ago, they were able to detach themselves from the water by developing waterproof skin and other ways of controlling water loss.
New research may have consigned the classic egg model from the textbooks to the trash
“But the amniotic fluid was key.
“It was said to be a ‘private pond’ in which the developing reptile was protected from drying out in the warm climates and allowed the Amniota to move away from the water’s edge and dominate terrestrial ecosystems.”
He added: “Our work, and that of many others over the years, has relegated the classic ‘reptilian egg’ model from textbooks to the trash.”
Project leader Professor Baoyu Jiang added, “This default view has been challenged.
“Biologists had noticed that many lizards and snakes show a flexible reproductive strategy about oviparity and liveliness.
“Sometimes closely related species exhibit both behaviors, and it turns out that viviparous lizards can return to egg-laying much more easily than had been assumed.”
The research, conducted by researchers from Nanjing University and the University of Bristol, is published in Nature Ecology & Evolution.