Human evolution, fire and smoke


This video says about itself:

Smoking Causes Cancer, Heart Disease, Emphysema

20 jul. 2012

This 3D medical animation created by Nucleus Medical Media shows the health risks of smoking tobacco.

ID#: ANH12071

Transcript:

Every time you smoke a cigarette, toxic gases pass into your lungs, then into your bloodstream, where they spread to every organ in your body. A cigarette is made using the tobacco leaf, which contains nicotine and a variety of other compounds. As the tobacco and compounds burn, they release thousands of dangerous chemicals, including over forty known to cause cancer. Cigarette smoke contains the poisonous gases carbon monoxide and nitrogen oxide, as well as trace amounts of cancer-causing radioactive particles. All forms of tobacco are dangerous, including cigars, pipes, and smokeless tobacco, such as chewing tobacco and snuff.

Nicotine is an addictive chemical in tobacco. Smoking causes death. People who smoke typically die at an earlier age than non-smokers. In fact, 1 of every 5 deaths in the United States is linked to cigarette smoking.

If you smoke, your risk for major health problems increases dramatically, including: heart disease, heart attack, stroke, lung cancer, and death from chronic obstructive pulmonary disease.

Smoking causes cardiovascular disease.

When nicotine flows through your adrenal glands, it stimulates the release of epinephrine, a hormone that raises your blood pressure. In addition, nicotine and carbon monoxide can damage the lining of the inner walls in your arteries. Fatty deposits, called plaque, can build up at these injury sites and become large enough to narrow the arteries and severely reduce blood flow, resulting in a condition called atherosclerosis. In coronary artery disease, atherosclerosis narrows the arteries that supply the heart, which reduces the supply of oxygen to your heart muscle, increasing your risk for a heart attack. Smoking also raises your risk for blood clots because it causes platelets in your blood to clump together. Smoking increases your risk for peripheral vascular disease, in which atherosclerotic plaques block the large arteries in your arms and legs. Smoking can also cause an abdominal aortic aneurysm, which is a swelling or weakening of your aorta where it runs through your abdomen.

Smoking damages two main parts of your lungs: your airways, also called bronchial tubes, and small air sacs called alveoli. Cigarette smoke irritates the lining of your bronchial tubes, causing them to swell and make mucus. Cigarette smoke also slows the movement of your cilia, causing some of the smoke and mucus to stay in your lungs. While you are sleeping, some of the cilia recover and start pushing more pollutants and mucus out of your lungs. When you wake up, your body attempts to expel this material by coughing repeatedly, a condition known as smoker’s cough. Over time, chronic bronchitis develops as your cilia stop working, your airways become clogged with scars and mucus, and breathing becomes difficult.

Your lungs are now more vulnerable to further disease. Cigarette smoke also damages your alveoli, making it harder for oxygen and carbon dioxide to exchange with your blood. Over time, so little oxygen can reach your blood that you may develop emphysema, a condition in which you must gasp for every breath and wear an oxygen tube under your nose in order to breathe.

Chronic bronchitis and emphysema are collectively called chronic obstructive pulmonary disease, or COPD. COPD is a gradual loss of the ability to breathe for which there is no cure.

Cigarette smoke contains at least 40 cancer-causing substances, called carcinogens, including cyanide, formaldehyde, benzene, and ammonia. In your body, healthy cells grow, make new cells, then die. Genetic material inside each cell, called DNA, directs this process. If you smoke, toxic chemicals can damage the DNA in your healthy cells. As a result, your damaged cells create new unhealthy cells, which grow out of control and may spread to other parts of your body. Cigarettes can cause cancer in other parts of your body, such as: in the blood and bone marrow, mouth, larynx, throat, esophagus, stomach, pancreas, kidney, bladder, uterus, and cervix.

Smoking can cause infertility in both men and women. If a woman is pregnant and smokes during pregnancy, she exposes her baby to the cigarette’s poisonous chemicals, causing a greater risk of: low birth weight, miscarriage, preterm delivery, stillbirth, infant death, and sudden infant death syndrome. Smoking is also dangerous if a mother is breastfeeding. Nicotine passes to the baby through breast milk, and can cause restlessness, rapid heartbeat, vomiting, interrupted sleep, or diarrhea.

Other health effects of smoking include: low bone density and increased risk for hip fracture among women; gum disease, often leading to tooth loss and surgery; immune system dysfunction and delayed wound healing; and sexual impotence in men.

From Leiden University in the Netherlands:

Are modern humans simply bad at smoking?

Published on 21 September 2016

Scientists looked for the genetic footprint of fire use in our genes, but found that our prehistoric cousins – the Neanderthals – and even the great apes seem better at dealing with the toxins in smoke than modern humans.

Mixed blessing

The art of making and using fire was one of the greatest discoveries ‘ever made by man’, wrote Charles Darwin. Besides providing protection against cold temperatures, the use of fire in food preparation and the introduction of energy-rich cooked foods in our prehistoric diet had a major impact in the development of humankind. However, fire use comes at a cost. Exposure to the toxic compounds in smoke carries major risks for developing pneumonia, adverse pregnancy outcomes in women and reduced sperm quality in males, as well as cataracts, tuberculosis, heart disease, and chronic lung disease. In short, the use of fire is a mixed blessing.

Debate

This mixed blessing, however, put researchers at Leiden University and Wageningen University on the trail of finding genetic markers for the use of fire in prehistoric and recent humans. The use of fire is notoriously difficult to ‘see’ for archaeologists, and this has led to strong disagreement over the history of its usage. A very early start is advocated by Harvard primatologist Richard Wrangham, who argues that our Homo erectus ancestors were already using fire around two million years ago. However, numerous excavations and intensive research carried out by archaeologists in Europe and the Near East suggest that control of fire occurred much later, around 350,000 years ago.

Genetic markers for fire use

In order to bring fresh data into this ‘hot’ debate, the Leiden/Wageningen team studied the biological adaptations of prehistoric and recent humans to the toxic compounds of smoke: fire usage implies frequent exposure to hazardous compounds from smoke and heated food, which is expected to result in the selection of gene variants conferring an improved defence against these toxic compounds. To study whether such genetic selection indeed occurred, the team investigated the gene variants occurring in Neanderthals, in Denisovans (contemporaries of the Neanderthals, more related to them than to modern humans), and in prehistoric modern humans.

Tobacco

Single nucleotide variants in 19 genes were tested that are known from modern tobacco-smoking studies to increase the risk of fertility and reproduction problems when exposed to smoke and hazardous compounds formed in heated food.

These genes were compared with variants observed in Neanderthals and their Denisovan cousins, and were also studied in chimpanzees and gorillas, two closely related species that are obviously not using fire, and are therefore not exposed to smoke on a regular basis.

Neanderthal more efficient in handling smoke?

In a study now published in PLOS ONE, the team shows that Neanderthals and the Denisovan predominantly possessed gene variants that were more efficient in handling the toxic compounds in smoke than modern humans. Surprisingly, these efficient variants were also observed in chimpanzees and gorillas, and therefore appeared to be evolutionary very old (ancestral) variants.

Plant toxins

The less efficient variants are observable from the first modern human hunter-gatherers for which we have genetic information onward, i.e. from about 40,000 years ago. The efficient defence against toxic compounds in chimpanzees and gorillas may be related to the toxins in their plant food. Smoke defence capacities in humans apparently hitchhike on those adaptations, developed deep in our primate past. Our prehistoric ancestors were probably already good at dealing with the toxic compounds of smoke, long before they started producing it through their campfires. What allowed for the emergence of less efficient hazardous chemical defence genes in modern humans is a question for future research.

Seabird evolution, new study


This 2014 video from Britain is called BBC Natural World – Saving Our Seabirds – Full Documentary.

From the Journal of Ornithology:

31 May 2015

Speciation in seabirds: why are there so many species…and why aren’t there more?

Vicki L. Friesen

Abstract

Speciation—the multiplication of species through the evolution of barriers to reproduction between populations—plays a central role in evolution since it enables two or more populations to adapt and evolve independently. However, mechanisms of speciation are notoriously difficult to study and poorly understood.

Seabirds provide useful models to investigate factors that may promote or inhibit speciation because their ecology and evolutionary genetics are relatively well understood. Here I review population genetic studies of seabirds to test the importance of six factors with the potential to disrupt gene flow enough to result in speciation.

Over 200 studies, including over 100 species, have been published to date. Most show evidence of restrictions in gene flow. Physical (geographic) barriers to dispersal are clearly important: conspecific populations that are separated by large expanses of land or ice show evidence of restricted gene flow, and sister species often are separated by physical barriers to gene flow. However, many species of seabirds show evidence of restrictions in gene flow in the absence of physical barriers to dispersal.

Study results indicate that differences in ocean regimes, nonbreeding distributions, foraging distributions during the breeding season, and breeding phenology also can disrupt gene flow enough to lead to speciation. Of these, physical isolation and differences in ocean regime appear to be the most important. Philopatry alone may be sufficient to result in reproductive isolation, but usually it acts in combination with other barriers to gene flow.

The effects of many other potential influences on gene flow need to be investigated more thoroughly, including colony distribution/location, wind, interspecific interactions, environmental stability/variability, variation in phenotypic traits associated with mate choice (morphology, behaviour, vocalisations) and intrinsic (genomic) incompatabilities. Recent advances in genome sequencing, especially if used in combination with ecological tools such as geolocators and new methods for data interpretation, are opening exiting new avenues to test the importance of various behavioural, ecological, demographic and genomic factors in reducing or promoting gene flow and so affecting speciation.

Evolution biology on trial in Tennessee, USA


This video from the USA is called The Scopes Monkey Trial Explained in 5 Minutes: US History Review.

By Peter Frost in Britain:

Primate witness: the monkey trials go on

Thursday 7th May 2017

PETER FROST is amazed that, 90 years after the famous Tennessee trial, the evolution versus creationism argument still rages

ON MAY 5 1925, 90 years ago this week, a group of thinkers in the small town of Dayton, Tennessee, are discussing a newspaper announcement.

The American Civil Liberties Union (ACLU) is looking for someone to challenge the new Butler Act passed by the state to outlaw the teaching of evolution in Tennessee schools. This law bans the teaching of any theory that denies the literal truth of the biblical creation of man.

One of the men, 24-year-old science teacher and football coach John Thomas Scopes, says he will be willing to be indicted to bring the case to trial. Scopes has only taught biology as a substitute teacher and later says he isn’t sure he covered evolution in his classes.

On May 25 John Scopes was brought to trial for teaching evolution. The case, forever known as the Monkey Trial, made world headlines and is still talked about today.

Scopes agreed to purposely incriminate himself so that the case could have a defendant. He knew such a trial would draw intense national publicity to the argument. The world’s press flocked to Dayton. To make room for the many journalists and observers the trial was convened in the open air. This proved a blessing in the stifling Tennessee heat.

Defending Scopes was Clarence Darrow, already a famous lawyer. He would go on to become the best-known and most revered defence lawyer in US jurisprudence.

Darrow had made his reputation as a labour union lawyer and had defended many militant heroes of US working-class strikes and struggles — many of them framed on trumped-up charges. These included many members of the US Communist Party charged with treason. Leading the prosecution of Scopes was William Jennings Bryan, Bible scholar, rabid creationist and three-time Democratic candidate for US president.

Bryan’s argument was simple. He declared the word of God as revealed in the Bible took priority over all other human knowledge. Judge John T Raulston made no pretence at neutrality. He started each day with a hymn and a prayer. The judge ruled that the many scientists who wished to speak in Scopes’s defence could only give their evidence in writing.

British novelist H G Wells was asked if he would join the defence team. Wells replied that he had no legal training in Britain, let alone in the US, and declined the offer. The ACLU opposed the Butler Act on the grounds that it violated the teacher’s individual rights and academic freedom, and was therefore unconstitutional.

Darrow and the judge frequently clashed and there were several threats of action for contempt with Darrow forced to apologise. Darrow attacked the literal interpretation of the Bible as well as Bryan’s limited knowledge of other religions and science. He scoffed at Bryan’s horror that human beings were descended “not even from American monkeys, but from old-world monkeys.”

Darrow took the unorthodox step of calling Bryan, the chief prosecutor, to the stand as a defence witness. Darrow asked him questions such as: “If Eve was actually created from Adam’s rib, where did Cain get his wife?” The confrontation between Bryan and Darrow lasted approximately two hours before Judge Raulston’s announced that he considered the whole examination irrelevant to the case. He ruled that it should be struck from the record. Darrow closed the case for the defence without a final summing up. Under Tennessee law, when the defence waived its right to make a closing speech, the prosecution was also barred from summing up its case.

Scopes was found guilty and ordered to pay a $100 fine. He addressed the court for the first time. “Your honour, I feel that I have been convicted of violating an unjust statute. I will continue in the future, as I have in the past, to oppose this law in any way I can. Any other action would be in violation of my ideal of academic freedom — that is, to teach the truth as guaranteed in our constitution, of personal and religious freedom. I think the fine is unjust.”

The appeal court set aside the conviction because of a tiny legal technicality: the jury should have decided the fine, not the judge, since under the state constitution Tennessee judges could not set fines above $50, and the Butler Act specified a minimum fine of $100. Appeal judge Green added: “We see nothing to be gained by prolonging the life of this bizarre case.”

The Butler Act stayed on the statute books until 1967. In reality this bizarre case and the arguments that caused it are still being debated. Strangely despite logic and scientific proof, the ideas of creationism are still gaining ground on both sides of the Atlantic.

When the Con-Dem coalition established free schools in 2011, three such schools — each teaching creationism — were approved by the then education secretary Michael Gove. Today free schools in Britain are no longer allowed to teach creationism as if it were fact. Now such teaching is confined to religious education classes and not presented as a valid alternative to established scientific theory.

Yet surveys show that, amazingly, one in three US citizens doesn’t believe in evolution. They think humans and other living things have existed in their present form since the beginning of time. White evangelical Protestants, particularly in the Southern Bible belt — states like Tennessee — are most likely to not believe in evolution and ridicule Darwin’s ideas.

Both Tennessee and Louisiana allow the teaching of creationism in school science classes. Currently, less than half of Republican voters, just 43 per cent, believe in human evolution. Only 67 per cent of Democrats think Darwin’s theory credible.

Worse, US opinion is shifting and the numbers doubting evolution and supporting creationism are growing every year. Nearly a dozen states are considering legislation to either outlaw the teaching of Darwinian evolution or to give equal space and time to creationism in school science classes.

In Tennessee the law defines controversial issues including biological evolution, the chemical origins of life, global warming and human cloning and seeks to ensure schools also teach what the Bible has to say on the subjects.

Tennessee law wrongly suggests the scientific community is divided over these issues. It is not, but the law has now made it significantly harder to ensure that science is taught responsibly.

Evolution, Darwin, Wallace and Patrick Matthew


This video says about itself:

Forsdyke Evolution Academy 01-14 Patrick Matthew

12 October 2011

The second of a series of 12 videos on natural selection from a historical perspective.

From King’s College London in England:

April 20, 2015

The overlooked third man

The horticulturist who came up with the concept of ‘evolution by natural selection‘ 27 years before Charles Darwin did should be more widely acknowledged for his contribution, states a new paper by a King’s College London geneticist.

The paper, published in the Biological Journal of the Linnean Society, argues that Patrick Matthew deserves to be considered alongside Charles Darwin and Alfred Russel Wallace as one of the three originators of the idea of large-scale evolution by .

Furthermore, Matthew’s version of evolution by natural section captures a valuable aspect of the theory that isn’t so clear in Darwin‘s version – namely, that natural selection is a deductive certainty more akin to a ‘law’ than a hypothesis or theory to be tested.

Patrick Matthew (1790-1874) was a Scottish landowner with a keen interest in politics and agronomy. He established extensive orchards of apples and pears on his estate at Gourdie Hill, Perthshire, and became adept in horticulture, silviculture and agriculture.

Whilst Darwin and Wallace‘s 1858 paper to the Linnean Society, On the Origin of Species, secured their place in the history books, Matthew had set out similar ideas 27 years earlier in his book On Naval Timber and Arboriculture. The book, published in 1831, addressed best practices for the cultivation of trees for shipbuilding, but also expanded on his concept of natural selection.

“There is a law universal in nature, tending to render every reproductive being the best possibly suited to its condition that its kind, or that organized matter, is susceptible of, which appears intended to model the physical and mental or instinctive powers, to their highest perfection, and to continue them so. This law sustains the lion in his strength, the hare in her swiftness, and the fox in his wiles.” (Matthew, 1831: 364)

In 1860, Matthew wrote to point out the parallels with his prior work, several months after the publication of On the origin of species. Darwin publically wrote in 1860 “I freely acknowledge that Mr. Matthew has anticipated by many years the explanation which I have offered of the origin of species”, while Wallace wrote publically in 1879 of “how fully and clearly Mr. Matthew apprehended the theory of natural selection, as well as the existence of more obscure laws of evolution, many years in advance of Mr. Darwin and myself”, and further declared Matthew to be “one of the most original thinkers of the first half of the 19th century”. However, both asserted their formulations were independent of Matthew’s.

Even if Matthew did not influence Darwin and Wallace, his writings provide a valuable third point of reference on the notion of macroevolution by natural selection, argues the paper’s author, Dr Michael Weale. Dr Weale has created a public website to act as an online repository of the writings by Patrick Matthew, including some of his lesser-known work.

Dr Michael Weale, from the Department of Medical and Molecular Genetics at King’s College London, said: ‘Whilst Darwin and Wallace both deserve recognition for their work, Matthew, the outsider who deduced his idea as part of a grand scheme of a purposeful universe, is the overlooked third man in the story. Matthew’s story is an object lesson in the perils of low-impact publishing. Despite its brevity, and to some extent because of it, Matthew’s work merits our renewed attention.’

Explore further: Darwin’s finches highlight the unity of all life

More information: ‘Patrick Matthew’s Law of Natural Selection’ by Michael Weale is published in the Biological Journal of the Linnean Society and can be accessed here.

From Wikipedia:

Matthew’s idea on society were radical for their times. Although he was a landowner, he was involved with the Chartist movement, and argued that institutions of “hereditary nobility” were detrimental to society. It has been suggested that these views worked against acceptance of his theory of natural selection, being politically incorrect at the time (see Barker, 2001).

Fossils collected by Charles Darwin: here.

Sea snail venom evolution, new research


This video says about itself:

11 January 2012

You’d think a snail wouldn’t be much threat in the sea, but the cone snail proves deadly to unsuspecting fish.

From the University of Michigan in the USA:

Predatory Snails Evolved Diverse Venoms to Subdue a Wide Range of Prey Species

Released: 17-Mar-2015 8:00 AM EDT

ANN ARBOR—A new study by University of Michigan biologists suggests that some predatory marine cone snails evolved a highly diverse set of venoms that enables them to capture and paralyze a broad range of prey species.

When cone snails sink their harpoon-like teeth into their prey, they inject paralyzing venoms made from a potent mix of more than 100 different neurotoxins known as conotoxins.

The genes that provide the recipes for conotoxin cocktails are among the fastest-evolving genes in the animal kingdom, enabling these snails to constantly refine their venoms to more precisely target the neuromuscular systems of their prey.

U-M researchers showed that the mix of neurotoxins in cone-snail venom varies from place to place and is more diverse at locations where the snails have a broad range of prey species. In addition, they concluded that the observed patterns of local conotoxin variation are likely due to natural selection.

That’s a significant finding because it is often difficult for biologists to determine whether place-to-place variations in an organism’s observable traits—the wide range of beak sizes and shapes in the Galapagos Islands finches studied by Charles Darwin, for example—are the result of evolution by natural selection or some other factor, such as the reproductive isolation of a population of animals or plants.

In addition, the U-M researchers were able to directly target the genes responsible for the observed conotoxin patterns. A paper summarizing the work is scheduled for online publication in the journal Proceedings of the Royal Society B on March 18.

“The differences in venom composition that we observed correspond to differences in prey, and a higher diversity of venom is used to capture more prey species,” said first author Dan Chang, formerly a doctoral student in the U-M Department of Ecology and Evolutionary Biology and now a postdoctoral researcher at the University of California, Santa Cruz.

“Our results suggest that prey diversity affects the evolution of predation genes and imply that these predators develop a more diverse venom repertoire in order to effectively subdue a broader range of prey species,” Chang said.

The study involved a common species of tropical, worm-eating cone snail, Conus ebraeus, collected at locations in Hawaii, Guam and American Samoa. These snails are about an inch long and are commonly known as Hebrew cone snails. Their shells are white with black rectangular markings that form a distinctive checkerboard pattern.

The researchers characterized the patterns of genetic variation in five toxin genes in C. ebraeus snails from the three locations. They also collected fecal samples from the snails to determine the types of worms they ate.

“We demonstrated that venom genes used for predation are highly affected by local variation in prey diversity and geographic heterogeneity in prey compositions,” Chang said. “Not all conotoxin genes are affected in the same way though, which implies that these genes may have distinct functional roles and evolutionary pathways.”

The other U-M authors are Thomas Duda and Amy Olenzek. The study was funded by a National Science Foundation grant to Duda, who is an associate professor in the Department of Ecology and Evolutionary Biology and an associate curator at the U-M Museum of Zoology.

Dan Chang
Thomas Duda

‘Conus geographus, the Life and Death Cone Snail’ by Andreia Salvador: here.

The plant family Corsiaceae, new research


This video is called Liliaceae plant family, description, examples, info.

From the Journal of Biogeography:

Ancient Gondwana break-up explains the distribution of the mycoheterotrophic family Corsiaceae (Liliales)

19 FEB 2015

Abstract

Aim

Many plant families have a disjunct distribution across the southern Pacific Ocean, including the mycoheterotrophic family Corsiaceae, which provides a prime example of this biogeographical pattern. A better grasp of the family’s evolutionary relationships is needed to understand its historical biogeography. We therefore aimed to (1) test the uncertain monophyly of Corsiaceae, (2) define its phylogenetic position, and (3) estimate divergence times for the family, allowing us to assess whether the distribution of the family is the result of vicariance.

Location

Southern South America and Australasia.

Methods

We analysed various combinations of mitochondrial and nuclear data to address the monophyly, phylogenetic position and age of Corsiaceae. To test its monophyly, we used a three-locus data set including most monocot orders, and to infer its exact phylogenetic position, we used a five-locus extended data set. We corroborated these findings using an independent plastome dataset. We then used a two-locus dataset with taxa from all monocot orders, and a three-locus dataset containing only taxa of Liliales, to estimate divergence times using a fossil-calibrated uncorrelated lognormal relaxed-clock approach.

Results

Corsiaceae is a monophyletic family and the sister group of Campynemataceae. This clade is the sister group of all other Liliales. The crown age of Corsiaceae is estimated to be 53 Ma (95% confidence interval 30–76 Ma).

Main conclusions

Corsiaceae is an ancient family of mycoheterotrophic plants, whose crown age overlaps with the plate-tectonic split of Gondwana, consistent with a vicariance-based explanation for its current distribution.

See also here.

Worst ever ice age and first animals, 715 million years ago


This video is called Precambrian Ediacaran Life Before the Cambrian Explosion 600 million years ago.

From the BBC:

Earth was a frozen snowball when animals first evolved

715 million years ago the entire planet was encased in snow and ice. This frozen wasteland may have been the birthplace of complex animals

Presented by Kate Ravilious

The ice brought Earth to a standstill. Where there were once waves lapping onto a tropical shore and warm waters teeming with life, there was just the whistling of the wind and a cold barren landscape, covered in ice as far as the eye could see. Even at the equator – the warmest place on Earth – the average temperature was a frigid -20°C, equivalent to modern-day Antarctica. Most life was wiped out, and the creatures that did survive huddled in small pockets of open water, where hot springs continued to bubble up.

This was “Snowball Earth” – a deep freeze that began around 715 million years ago and held Earth in its icy grip for a good 120 million years. “There are no other comparable glacial periods on Earth. This one was really quite catastrophic,” says Graham Shields of University College London in the UK.

However, some scientists now believe that this crushing catastrophe drove one of the most incredible steps in evolution: the development of the first animals, and a dramatic flourishing of life known as the Cambrian explosion.

Around 540 million years ago, a host of exotic creatures suddenly appeared. They included giant woodlouse-like creatures known as trilobites, the five-eyed Opabinia, and the spiny slug-like Wiwaxia. Suddenly, Earth leapt from being dominated by single-celled bacteria to a world teeming with exotic multicellular creatures, all in a geological blink of an eye.

This video shows a reconstruction of the extinct animal Opabinia.

The Cambrian explosion remains a puzzle

For Charles Darwin, trying to demonstrate his theory of natural selection, this sudden burst of evolution was a major problem. “The case must at present remain inexplicable; and may be truly urged as a valid argument against the views here entertained,” he wrote in On the Origin of Species in 1859.

To this day the Cambrian explosion remains a puzzle. But maybe a planet-encasing icy catastrophe could help explain it.

The evidence for a Snowball Earth first emerged in the early 1990s. Unexpectedly, geologists discovered evidence of glaciers – such as stones that had clearly been carried on ice rafts and then dropped – in the tropics. Since then, a growing body of evidence has shown that the global deep freeze began around 715 million years ago, and lasted nearly 120 million years.

Exactly how far the ice extended is still debated. Some argue that the entire Earth was encased in ice, with just a few small pockets of open water where hot springs bubbled up. Others believe that a belt of open water remained around Earth’s equator.
Regardless of how far the ice stretched, most scientists agree that the Snowball formed suddenly. It was probably caused by rapid weathering of Earth’s continents, which sucked carbon dioxide – a planet-warming greenhouse gas – out of the atmosphere and caused temperatures to plummet. There were two distinct pulses of extreme glaciation, interspersed with a 20-million-year warm period. Finally, around 660 million years ago, Earth’s volcanoes topped up the atmospheric carbon dioxide enough to haul the climate out of its frozen state.

So why on Earth would this period of extreme cold cause life to switch gear so rapidly? Maybe, say many geologists, because it pumped lots of life-giving oxygen into the air.

The idea is that the ice gave a boost to microscopic plants, which released oxygen as a waste product. During the Snowball, the glaciers would have worn huge amounts of phosphorus-rich dust away from the underlying rocks. Then, when the ice retreated at the end of the Snowball, rivers washed this dust into the oceans, where it fed the microbes.

“High phosphorus levels would have increased biological productivity and organic carbon burial in the ocean, leading to a build-up of atmospheric oxygen,” says Noah Planavsky of Yale University in New Haven, Connecticut. In 2010 he identified a massive spike in phosphorus levels in sediments from around the world, just as Snowball Earth was ending.

That was suggestive, but in 2014 Planavsky found more direct evidence. His team estimated oxygen levels prior to Snowball Earth, by studying chromium – which exists in different states depending on the amount of oxygen in the air – in ancient rocks. Until 800 million years ago, atmospheric oxygen levels were just one-hundredth of today’s levels.

Planavsky thinks that is far too low to support complex animal life. “In modern low-oxygen environments there is less ecosystem complexity and a more limited range of animal behaviours,” says Planavsky. “So it is reasonable to expect that an oxygen rise would pave the way for animal and ecosystem diversification.”

But there’s a problem with that idea. Experiments published in 2014 showed that some animals can survive with much less oxygen than previously thought. Sponges, one of the oldest kinds of animal, need just 0.5% of modern oxygen levels. That suggests oxygen wasn’t enough of a trigger.

In recent years another idea has come to prominence. Maybe it was the ice itself that drove the evolutionary leap, says Richard Boyle of the University of Southern Denmark in Odense. “There are no animals more complex than a sponge prior to the last of the Snowball glaciation events, and in my opinion this is not coincidence,” says Boyle.

For Boyle the real puzzle isn’t the appearance of multicellular animals. Instead, it’s the rise of cellular differentiation – cells with specific roles like liver, muscle and blood. These specialised cells allowed animals to become much more intricate. “What sets animals apart from plants and fungi is this irreversible cellular differentiation, which, for instance, is what allows animals to have more cell types,” says Boyle.

It’s hard to see how this could have evolved, because specialised cells lose the ability to reproduce on their own. Instead they have to be distinctly self-sacrificing, cooperating with other cells in the body for the greater good of the animal. Only the specialised reproductive cells, the sperm and eggs, get to create a new generation.

By contrast, plants don’t just rely on specialist sex cells to reproduce. They can also reproduce themselves from cuttings taken from their stems or roots. “You can’t take a cutting from an animal,” says Boyle. He thinks the severity of Snowball Earth may have pushed animal cells to abandon this flexibility, and specialise.

“During the Snowball period, life will have been confined to small geothermally heated areas, and will have experienced frequent extinctions and population crashes,” says Boyle. The populations that did survive were often reduced to just a handful of organisms. Boyle suggests that these little groups of survivors were often closely related, encouraging them to cooperate more than usual.

Biologists have long known that animals are more likely to help close relatives, because by doing so they can benefit their own genes, which the relative will also carry. For example, wild animals are likely to adopt orphans that are related to them, but not orphans that are unrelated. Boyle thinks that Snowball Earth may have forced cells to behave altruistically. “Until that point, the cost of being an animal cell had been too high,” he says.

Boyle’s notion is controversial and other scientists are sceptical. “Boyle’s melt-hole idea for the origin of animals is fun,” says palaeontologist Nick Butterfield of the University of Cambridge, UK. “But most geologists don’t buy the idea of a hard Snowball Earth anymore, so the isolated hot-spring refugia ponds wouldn’t have actually existed.”

Butterfield argues that life probably retreated to the open waters of the tropics during Snowball times, but otherwise carried on as normal.

It would really help to find some definitive fossils to resolve this. Unfortunately, the fossil record is very patchy in such ancient rocks. So far, the oldest definitive fossils of complex animals date to around 560 million years ago. That could fit with either hypothesis.

Genetics doesn’t help much either. By working backwards through the animal family tree and estimating rates of genetic change, scientists have estimated that the first animals are likely to have emerged around 750 million years ago. But these “molecular clock” estimates are notoriously unreliable.

Nonetheless, recent discoveries hint that animal life may have started to gain a foothold during Snowball Earth. In 2014, Malcolm Wallace of the University of Melbourne in Australia discovered strange clumps of fossils in remote regions of Australia and Namibia. In the remains of ancient reefs, Wallace found bubble-shaped fossils up to 3cm across. Many of the bubbles appeared to interconnect into a network of finger-like strands.

“These fossils are big and complex, but they don’t really fit exactly into any of the animal phyla,” says Wallace. They date from around 700 million years ago, soon after Earth first became a Snowball.

So Wallace and his colleagues think they may have found the precursors to animals – very early sponge-like creatures, which lived in low-oxygen waters and represented a halfway stage between single-celled microbes and multicellular animals. And they think it is no coincidence that these animal precursors appear right after the first major Snowball glaciation.

“Intuitively, you might think that Snowball Earth would hinder evolution, and yet animals appear soon after the big glaciations,” says Wallace. “It seems clear that these big glaciations have disrupted the Earth’s ocean-atmosphere system in some way that was favourable for complex life to develop.”

Boyle agrees that this kind of primitive animal life may have evolved before the end of Snowball Earth, but he argues that this wasn’t the crucial step. Instead, the key threshold is when individual cells forgo their ability to reproduce, and instead take on specific roles within an animal.

So far, animals more complex than sponges, with specialised organs that do different jobs, have only been found in rocks laid down after the Snowball. Boyle predicts that they will never be found in older rocks, certainly not in rocks laid down before the Snowball. “If such fossils are found then my hypothesis will be proven incorrect,” he says.

Butterfield agrees that such ancient animal fossils may never turn up, but that could simply be because they haven’t been preserved. He now suspects that Boyle, Planavsky and Wallace have got the whole story backwards. Instead of the ice creating complex animals, he suggests that the first animals appeared 750 million years ago and transformed the planet, cooling the climate. “I think there is a good case to be made for the evolution of animals actually triggering the glaciations,” says Butterfield.

“Animals have an enormous capacity to modify physical environments,” says Butterfield. So he thinks the first animals upset the delicate balance of ocean chemistry, with knock-on effects for the rest of the planet.

Animals can certainly have big effects on the planet. For instance, burrowing animals like worms can break up rocks faster. The resulting rock dust reacts with carbon dioxide in the air, and the minerals produced get washed into the oceans – removing the carbon dioxide from the air. Meanwhile, marine animals boost oxygen levels by eating the remains of dead organisms, which would otherwise consume oxygen. Butterfield also thinks animals may have driven the evolution of new microscopic plants that sank faster, taking carbon dioxide with them.

There is some evidence that the first animals could have thrown Earth into a deep freeze. In 2011, Eli Tziperman of Harvard University in Cambridge, Massachusetts and his colleagues modelled the chemical cycles in the ocean. They found that the evolution of new marine organisms could have helped transport more carbon to the ocean floor and forced a major change in climate. “It’s certainly not unreasonable to suggest that the evolution of animals initiated glaciation,” says Butterfield.

Right now there’s not enough information to decide whether animals created Snowball Earth, or Snowball Earth triggered animal evolution. But either way, the two events are linked.

They are also a sobering reminder of how quickly conditions on Earth can change. Our planet has been just right for us for thousands of years, but there is no reason to believe it will stay that way.

Right now our appetite for fossil fuels is hotting things up dangerously fast. But a large asteroid impact, like the one that did for the dinosaurs, would throw up enough dust to block sunlight and cause a dangerous chill. And because today’s oceans are cooler than they were in the dinosaurs’ time it’s conceivable that the oceans would freeze and Earth would revert to a Snowball state.

Whether our planet goes hot or cold, it will be a seriously bumpy ride. Maybe we should learn from those early animal cells, and learn to work together.

Methane didn’t warm ancient Earth, new simulations suggest. Alternative explanation needed for why planet didn’t freeze despite dim sun: here.