The term "sheep" is also a metaphor for people who follow en masse without question.

But sheep are not mundane mindless mammals — not in the slightest.

There's plenty going on behind their horizontal pupils.

They're clever creatures, deftly thwarting our defences to get to the greener grass (or flowers, as you'll discover) on the other side.

Sheep can recognise and remember dozens of sheep faces. They can also recognise human faces, and like us, they prefer them when they're smiling.

And they've contributed far more to human existence than lamb chops and cosy jumpers.

Their history stretches back millions of years, when …

Sheep ancestors popped up in central Asia

There are hundreds of domestic sheep breeds today, from the Turkish Acıpayam to Zulu sheep in South Africa, but they're pretty much all one species: Ovis aries.

Their earliest ancestors evolved between 10 and 20 million years ago in the mountains of central Asia, according to Sally Coulthard, historian and author of A Short History of the World according to Sheep.

"That really early predecessor split and went different ways and some trotted west, into Europe, some went east into China and Siberia … and some even crossed over what would have been the frozen Bering Strait and went into North America," she says.

As populations separated, and were domesticated and bred, they developed unusual features, such as the twirly spiral horns of the Racka ...

... and the North Ronaldsay, which lives on a remote Scottish island and eats only seaweed.

Flocks are dynamic:

It may not look like it as you drive past, but a flock of sheep in a paddock is a dynamic little system, splitting and rejoining as conditions change.

Sometimes they huddle together, and other times they spread apart — but rarely, if ever, do sheep hang out alone.

A team led by Stephan Leu, an animal behaviour researcher at the University of Adelaide, found a daily pattern to this ovine fission and fusion.

"The largest group sizes are early in the morning and late in the afternoon. And there's also another sort of peak in the middle of the day," Dr Leu says.

"They meet up with smaller subgroups and form these larger groups."

Those times coincide with lulls in sheep activity, when they forage less and rest more.

"The benefits of being in a larger group are, for instance, spotting predators," Dr Leu says.

"They form these larger groups to be protected because everyone is watching out for each other a little bit."

They're excellent problem-solvers:

Like many domesticated animals, sheep are clever creatures. They can solve complex mazes, and remember the solution weeks, even months, later.

This is something sheep farmer and YouTuber Tara Farms knows only too well.

If there's a hole in a fence, the sheep are on it.

"They know where to escape through the fence. You can take a sheep out of a paddock and put them back in there three months later and they'll still find the same hole, if you haven't patched it," Tara says.

"They know."

But the measure of sheep intelligence is perhaps best illustrated by a mystery that hit the English village of Marsden in 2004.

Something was eating the flowers in the village's flowerbeds, and residents simply could not work out who the culprit was.

There were sheep in the moors around Marsden, but the village was protected by sheep grids, and they were too wide for the sheep to leap over.

The residents finally decided to stay up overnight and watch — and what they saw amazed them.

"Apparently the sheep had learnt to do commando rolls over the sheep grids,"

The likeliest scenario was one or two sheep figured out they could lay on their side and roll across, then showed the rest of the flock, she adds.

"So not only is that showing amazing problem solving, but also the communication of knowledge, all of which are things that we associate with higher intelligence.

"Certainly after looking after sheep, I realise sheep are much cannier than people give them credit for."

They were used as contraception:

Before rubber, condoms could be made from animals, including sheep — their intestine, to be specific.

"Sheep gut is actually fabulously flexible and robust, and really useful," Coulthard says.

Some of the earliest evidence for condoms in Europe was found in the 1980s.

Archaeologists excavated a toilet at Dudley Castle near Birmingham in England, which was sealed in the middle of the 17th century.

Along with remains like coriander seeds and fish bones, the researchers found 10 animal membrane condoms.

Five were burnt and blackened, while the other five were nestled inside each other, like an intestine-condom-Matryoshka doll.

Making them took time and care, according to researchers who published the Dudley Castle condoms in Post-Medieval Archaeology.

The cut intestine was scraped, cleaned (possibly turned inside out), dried and cut to size, which was between 15 and 20 centimetres long.

"In many cases, the open end was trimmed with a ribbon tie," the researchers wrote.

They couldn't say whether the condoms were used primarily for contraception or to protect against sexually transmitted infections, but considering the laborious manufacturing process, a condom was a luxury at the time.

And there's a chance the Dudley Castle sheaths were not single-use.

"Whilst there is some dark staining on some of the Dudley Castle condom tips, some mottled dark patches also occur on … remains of the [condom] shafts; it is unclear whether or not these patches testify to repeated use," the researchers wrote.

Sheep have helped make babies too:

Advances in artificial insemination were largely thanks to sheep (and some scientists, of course).

Back in the 1950s, Australia was well and truly riding on the sheep's back.

The US needed wool to make uniforms for soldiers heading to the Korean war, and they bought much of it from Australia.

The price of wool skyrocketed.

Where before it sold for a few shillings per pound, woolgrowers suddenly got "a pound a pound".

Sheep needed to be bred to meet demand.

Artificial insemination, where sperm from a ram is inserted directly into a ewe's uterus, was a way to do it quickly.

A Hungarian agricultural scientist, who spent three years in a Siberian gulag then fled Europe during the 1956 Hungarian Revolution, would play a huge role in developing that technology.

That scientist — Steven Salamon — arrived in Australia, where he eventually made his way to the office of the University of Sydney's head of animal husbandry, Terry Robinson.

Professor Robinson recognised Dr Salamon's talent.

They led a team that developed ways to freeze sheep sperm, and modify the female reproductive cycle so a bunch of ewes could become pregnant at the same time.

Artificial insemination was born.

And it worked, says Gareth Evans, an animal reproduction researcher at the University of Sydney.

"If you get a particularly valuable ram, it might be able to cover 50 ewes or something in a season … whereas it could be many hundreds through artificial insemination," Professor Evans says.

These days, artificial insemination — sometimes known as intrauterine insemination — is a fertility treatment for human animals too.

As is in-vitro fertilisation or IVF … and this had its origins in sheep, too.

In the 1960s, a young agricultural scientist named Alan Trounson, working in a southern NSW woolshed, wondered why some sheep had more lambs than others.

He soon realised it came down to the number of eggs the ewes produced.

After studying embryology, he and collaborators worked on a solution for women who were struggling to conceive. It involved increasing egg production, which increased their likelihood of falling pregnant — just like he'd seen in sheep.

And these days, one in 18 babies in Australia is born via IVF.

Original Story By | Ann Jones, Petria Ladgrove & Belinda Smith