HOW MAN BECAME MONOGAMOUS, LOST HIS FUR, GOT BLACK SKIN AND THEN BECAME BLONDE

Homo erectus, the direct ancestor of Homo sapiens, evolved in Africa between 2 and 1.5 million years ago (Mya). He was the same size as us, walked and ran erect. He made Acheulean stone axes for hunting and for scavenging big mammals killed by other predators. He built low stone walls, with animal skin tents above, or lived in caves with fire to keep him warm. He dressed in hide and fur when cold.

Homo erectus was very successful, spread out from Africa and lived all over Europe and Asia. But his brain size was smaller than humans and childhood period was shorter. He used proto language and formed social groups. Total numbers of these hunter gatherers were probably small, maybe 1- 200,000 at the peak, spread out all over Asia, Africa and Europe in small clans.

The Australopithecines and earlier hominins that preceded Homo erectus walked upright when forests in East and South Africa grew drier around 4 Mya, making it necessary to forage outside tree cover. As brain size increased, the period of infancy and childhood increased too, needing prolonged care. Australipithecus became monogamous so that males could forage and carry back food for his family in his hands. Bringing back fruit, nuts and roots with occasional meat made increasing brain size possible – in turn making him a better forrager – a beneficial cycle of walking, carring back better quality food, and increasing brain size.

Human ancestors probably remained largely monogamous after that, unlike Chimpanzees and monkeys. Australipithecus and Homo erectus both show reduced sexual dimorphism. Males and females looked alike and were of similar size, indicating reduced competition for mates. By 2.5 Mya, many parts of Africa changed from scrub or forest to open Savannah similar to the Serengeti plains of today. Herbivores abounded and Homo erectus adopted a predominantly meat diet. His intestines elongated and the cecum shortened, making him a well adapted carnivore. He cracked bone with stone axes for marrow and cooked his meat which increases nutritive value.

Australipithecus had fur. Homo erectus lost his fur so that he could run faster in day time hunting. Sweating from increasingly numerous sweat glands kept him cool in the hot sun. Long legs increased speed and cooling. Retained hair on head protected skull knocks, beard protected fist fights, pheromones and friction dictated pubic and armpit hair. Fur everywhere else vanished.

Furred creatures have white skin, which is not exposed to sunlight. After losing fur, Homo erectus acquired melanin producing enzymes 1.2 million years ago to protect from ultraviolet damage, which causes skin cancer. For ever after, until very recently, all men and their ancestors were dark skinned for this reason.

Homo erectus evolved into Homo heidelbergensis about 700,000 years ago. Heidelberg man hunted with stone tipped spears and moved out of Africa, replacing and maybe interbreeding with Homo erectus in most of Asia and Europe. In Europe and Siberia, Heidelberg man evolved into Neanderthals and Denisovans. In Africa Heidelberg man evolved and became Homo sapiens around 200,000 years ago. Modern man again spread out of Africa about 70,000 years ago, interbreeding with Neanderthals and Denisovans but ultimately replacing them. 1-3% of humans everywhere except Africa have Neanderthal and Denisovan genes. Some of them might have improved our immunity or increased our tolerance to high altitude. Elsewhere Homo erectus continued to live in small communities and became extinct only 115,000 years ago, at the end of the Eemian period.

It’s important to realise that humans evolved from very small numbers. Neanderthals had permanent long term habitation in Europe from 400,000 years ago, but were not very fertile, never numbering over 50,000 people. Modern man was more fertile and hence replaced Neanderthals despite better adaptation of Neanderthals to the cold weather of Ice Age Europe. By the start of Holocene in 9000 BC Modern Man alone survived, and might have numbered a few hundred thousand individuals all over the world.

DNA from Homo heidelbergensis, Neanderthals and Denisovans have been sequenced. So has archaic human DNA. The results throw up startling findings about skin color.

Homo erectus of Europe was black. Neanderthal man was black. Modern man living in Europe until about 8000 BC was also dark skinned, occasionally with blue eyes. Everywhere in Asia Africa America, humans were varying shades of brown and black. Never white.

Vitamin D production needs light skin and UV light. But folate gets degraded by UV, if skin is too light. Folate is necessary to prevent cancer. The balance between these two, drives the skin color of humans based on amount of sunlight available. People in tropics always evolved towards dark skin to protect against skin cancer and since that’s where H erectus and H sapiens evolved, they were all dark skinned.

Blonde hair evolved around 9000 BC probably starting from small populations in Russia. Pre agricultural human settlements were under stress at this time. The number of men decreased as hunting and scavenging became harder and some didn’t return from hunting. Much of the big mammal herds and predators progressively become extinct with the start of Holocene. Humans from other competing clans were a danger. As the number of women increased, the fewer men selected light skinned blonde haired women as their mate due to sexual selection, affecting the allele frequency. Once derived, the northern climate ensured better survival of light skinned humans due to Vitamin D related selection pressure, but had selection disadvantage at lower latitudes near equator. As agricultural techniques which developed around 7000 BC in the Levant spread west to Europe through the human population, these skin and hair colours spread too, as did the Indo Aryan language group.

Nowadays of course blonde hair comes from a bottle. Anybody can be a blonde, including Indians, removing selection pressure. With less than 2% of the current population having naturally blonde hair genes, within 200 years it is projected to die out. The majority of humans are projected to trend towards a neutral Latin American skin tone. 

And as child rearing is undertaken via mobile phone based social networks, time requirements of parenting are reducing. The vestiges of monogamy are likely to vanish very quickly indeed.

https://www.smithsonianmag.com/science-nature/becoming-human-the-evolution-of-walking-upright-13837658/

http://www.bbc.com/earth/story/20160801-our-weird-lack-of-hair-may-be-the-key-to-our-success

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https://www.google.com/amp/s/www.livescience.com/amp/63308-homo-erectus-laziness-extinction.html

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WE ARE CURRENTLY IN THE MIDDLE OF AN ICE AGE, BUT MOST OF US DON’T KNOW IT

An ice age is when one or both poles are permanently frozen. Like right now.

For most of the earth’s life, poles were not frozen. It was always summer - hot, humid and good for life to flourish. Called greenhouse phases, the average temperature of the earth was 30C (currently 15C).  Carbondioxide (CO2) was above 300 ppm (could reach 800 ppm or more). There was a greenhouse phase from 600 to 360 million years ago (Mya) i.e. lasting 240 million years and from 260 to 40 Mya (220 million years).

The Ice age previous to ours, called the Karoo Ice age, lasted from 360 to 260 Mya. Rodinia supercontinent split apart around 700 Mya. The pieces came together around 335 Mya to form another supercontinent called Pangea. Since the  Gondwana part of Pangea was in the South Pole region around 360 Mya, it got cold and the Karoo Ice age resulted. But only the poles got cold, like present day earth and unlike snowball earth of 2400-2100 Mya (Huronian) and 700-600 Mya (Cryogenian) when glaciation was extensive. During Karoo ice age there were carboniferous rain forests in the tropics which ultimately converted all carbondioxide to oxygen. CO2 fell from 800 ppm to below 300 ppm and oxygen levels went up causing more severe glaciation of poles around 300 Mya which ended the carboniferous era.

Evolution of termites ended the Karoo ice age, around 260 Mya. Termites digest lignin of even buried wood and their gut has methanogenic archaebacteria. Conversion of CO2 into wood and then coal occurred in swamp lands which by 260 Mya got submerged undersea, stopping the removal of carbon. Methane from termites accumulated. Forests died. CO2 and methane levels rose causing the global warming which ended the Karoo ice age. Later, 250 Mya there was a mass extinction of insects (Permian Triassic Extinction). We don’t know whether a meteor or volcano or climate change caused that.

It was hot and humid from 260 Mya. No ice caps. Cold blooded dinosaurs evolved and could roam the hot earth with ease. They got wiped out by a meteor falling into the Yucatan region around 65 Mya. It caused an impact winter because of dust in the atmosphere. All photosynthesis stopped. Winter lasted only a few thousand years but at the end of it, only creatures smaller than 25 Kilos survived. All else perished. We say the Era changed from Mesozoic to Cenozoic but the impact winter effects vanished fast and earth was hot again.

Things changed a bit when Pangea, which had split about 150 Mya, moved our continents to locations similar to present day (See figure – you can see India move up). 

Glaciers developed on Antarctica 40 Mya after Australia split off and moved up. A circumpolar sea current developed around Antarctica and cooled it. Northern hemisphere was not much affected. During Pliocene (10 Mya to 2.5 Mya) Co2 levels were around 400 ppm, not unlike today. Earth was warm and there was no ice in north pole.

The fourth and last Ice Age of Pleistocene started 2.5 Mya when the isthmus of Panama developed and stopped mixing of water between Pacific and Atantic. The north pole also froze. Wooly mammoths, wooly rhinos, sabre toothed cats etc evolved, just like the ice age movies.

As long as the Isthmus of Panama remains, earth will remain in an ice age.

Like the Karoo Ice age, Pleistocene was not a snowball earth. Africa, India, South America and South East Asia had climates pretty similar to what we have today, just a bit more arid with less rainfall. Homo erectus evolved 1.5 Mya in Africa and spread throughout the world, a scavenging nomad.

In the last 2.5 million years of the Pleistocene, there were interglacial periods when ice cover retreated. It happened every 100,000 years or so, brought about by solar maxima (Milankovitch cycles). Earth has a tilted axis which undergoes precession. Just like a spinning top, the axis moves in a circle every 26000 years. So every 13000 years earth faces more towards the sun and gets hotter. After another 13000 years it gets gets colder when axis tilts in reverse. Since orbit around sun is also eccentric, every 100,000 years or so the orbit and precession combine to make it hot enough for glaciers to melt a lot. Sometimes, sun spot activity also combines to accentuate or minimise these effects. These warm interglacial periods usually last for around 15000 years.

That’s where we are right now – an Interglacial period called Holocene.

Holocene started about 11600 years ago (or about 9000 BC) when we were at solar maximum with respect to axial tilt. It melted the glaciers and ended the ice age. Melting of float ice in sea doesn’t raise sea level but ice melt from European, Siberian and Canadian land mass does. Sea level rose by 60 meters or so (about the height of Qutab minar at 73m). Britain became an island because of channel ice melt. Sri Lanka became an island because sea levels rose to create Palk straits. Most of the giant mammals became extinct. Humans found conditions good for agriculture along the rivers and we became civilized, only ever knowning the interglacial period of Holocene in history.

The previous interglacial period is called the Eemian. It started 130,000 years ago and ended 115,000 years ago. It was hotter than the Holocene by about 1-2 degrees. CO2 was about 280 ppm, same as pre-industrial Holocene. It is during the Eemian that Homo sapiens developed.

Its interesting to note that during the Eemian, hippos roamed the Thames in London. Seas were 6-9 meters higher than today, including Baltic sea, making Norway and Sweden an island.

The Eemian ended when the earth’s axis tilted away, as expected, having lasted 15000 years. It iced over for 100,000 years after that. When we talk of “The Ice Age”, we normally mean the last 100,000 years. Global temperatures were around 10C and CO2 levels were around 200 ppm. Most human migrations from Africa occurred in this period as they went where prey were easier to catch, including the ice age mammals of Europe, Asia and the Americas. A few also came to India.

Many people don’t realise that we are now close to the solar minimum due to axial tilt. We have enjoyed 11600 years of warm interglacial period. In a few thousand years, the earth is due for another ice age. Our only long term hope is to prevent it using climate control technology.

One might think that global warming is good, as it prevents another ice age. But things aren’t so simple. As long as we stay where we are now, its “probably” fine.

But if earth warms too much, it causes a catastrophy. Global warming increases precipitation of rain and snow. Within a few hundred years, snow accumulates in the poles and an ice age develops. However, thats far away.

In the short run, within our lifetimes, a hot earth makes everything very unpleasant indeed. Cyclones, floods, blizzards, we get them all. The last few years have already indicated these dangers. We are a few crop failures away from a global famine. Any drastic global warming results in an out of control climate disaster.

We want things to stay stable until we do enough research and learn to control the climate properly, which might take a 100 years. Until then, lets keep our methane and CO2 emissions curtailed.

Just like every previous climate change, the issue is evolve or perish. The evolution demanded of us is to become better planet scientists able to control the factors which dictate our climate. The Pleistocene Ice Age we live in has given us just enough time to be able to do it – provided we don’t mess it up with backward Anti-Science mentalities.

 

Ref:

1. Pedersen RA, Langen PL, Vinther BM. The last interglacial climate: comparing direct and indirect impacts of insolation changes. Clim Dyn 2017;48:3391-3407

2. Salonen JS, Helmens KF, Brendryen J et al. Abrupt high-lattitude climate events and decoupled seasonal trends during the Eemian. Nature Communications 2018;9:2851

3. Wikipedia for the rest as on 19.7.20

Image created by screenshotting this video below:

https://m.youtube.com/watch?feature=share&v=WaUk94AdXPA

CLIMATE CATASTROPHY AND EVOLUTION: FOUR SIGNIFICANT EVENTS IN 4 BILLION YEARS

The earth formed 4.5 billion years ago. Ancestral archaea (archaebacteria) evolved from undersea hydrothermal vents 3.8 billion years ago when the earth was hot and fiery. The atmosphere was full of methane and carbon-dioxide (CO2). Archaea are the only organisms which produce methane, even now (apart from petroleum breakdown deep under the earth). Eubacteria evolved from ancestral archebacteria some 3.2 billion years ago but caused no climate change. For 1.3 billion years there was no oxygen in the air and the only life was bacteria. Until 2.5 billion years ago when one type of eubacteria evolved to acquire thylakoid membranes and photosynthesis, becoming Cyanobacteria.

This amazing thing has happened just once in the history of this earth. Flight for example has evolved four times independently (insects, pterodactyl, birds, bats) not counting many types of gliding.

This singular event of photosynthesis changed the face of the earth causing “The Great Oxygenation Event”. All the methane combined with oxygen to form CO2, which again got used up by Cyanobacteria. The oxygen killed off most of the bacterial types. With greenhouse gases (methane, CO2) gone, the earth cooled drastically. The whole of earth was like a ball of ice for 300 million years or so, from 2400 to 2100 million years ago (Mya), called the Huronian glaciation (from Lake Huron). Even the cyanobacteria were frozen and most of life stopped.

Oxygen caused the first climate catastrophy and a “Snowball earth”.

The Huronian glaciation ended 2100 Mya. It escaped that icy deep freeze because volcanos and moving tectonic plates released enough carbondioxide to warm the earth and life flourished again. A supercontinent called Columbia formed, as a result of these geological changes, lasting from 2000 to 1800 Mya. Only to break up again. The air was polluted with oxygen but life found a way and evolved to use oxygen now. An archaebacterial ancestor had evolved into eukaryotes, which unlike all bacteria, have a nucleus. Eukaryotes absorbed (a process called endosymbiosis) a type of eubacteria into the cytoplasm, which could efficiently use oxygen. These are now called mitochondria, being present in every cell and help in efficient oxygen utilization. Some eukaryotes further had endosymbiosis of cyanobacteria within them which turned into plastids, the chlorophyll substance of plants. These two types of still unicellular eukaryotes lived along with the archebacteria, eubacteria and cyanobacteria for 1.4 billion years (2100-700 Mya), evolving but without significant change.

Rodinia, another supercontinent formed 1100 Mya started breaking up by moving tectonic plates 700 Mya. Weather patterns changed, there was more rain and it froze causing 100 million years of deep freeze. The glaciation ended around 600 Mya due to volcanic eruptions. But a drastic change happened to life.  

600 Mya, as life bloomed again after the freeze, multicellular organisms evolved from different types of eukaryotes in multiple independent events to create plants (which has plastids derived from cyanobacterial thylakoids), animals (invertebrate and vertebrate) and others like fungi. Plants control cell growth using plant hormones. Animals control cell growth using apoptosis, a programmed cell death. Fungi grow with food, portions die without food to retreat and sporulate. All different means to become multicellular. To start with plants were small but when they evolved to acquire a hard protein called lignin 450 Mya, it made huge trees possible. Massive rainforests covered the earth in the carboniferous era from 350 to 290 Mya. CO2 levels were 800 ppm. This era converted enormous quantities of carbon into coal via fossilisation of trees. Ambhibians and Insects predominated the land animals.

It ended as before when plate tectonics changed the climate. The earth cooled. The “Carboniferous Rainforest Collapse” occurred. Thick forests turned into open tree fern covered land. Amphibians died in large numbers, Reptiles evolved and life moved on.

Going over 4 billion years of the earth’s life one sees four significant events.

a.      1. Photosynthesis by Cyanobacteria caused a snowball earth 2400 Mya

b.      2. Melting glaciation (Huronic) caused evolution of Eukaryotes 2100 Mya

c.       3. Second melting glaciation caused evolution of multicellular organisms 600 Mya

d.    4. A newly evolved protein called lignin (450 Mya) laid the groundwork of making the coal which today threatens yet another modern climate catastrophy

Each event is associated with climate change. Evolve or perish is the situation repeatedly created by our planet. Every time, life has evolved and not perished. These 4 billion years also created the present biomass balance where 80% is plants, Eubacteria including cyanobacteria 15%, Fungi 2%, Archaea 1%, Animals and rest 2%.

In that single last line is the secret to climate change and the balance of life which we as humans need to find. The future projected a thousand years from today is crystal clear. Either humans learn to fine tune earth’s climate. Or the earth turns into another snowball for thousands of years, because the end result of global warming is once again a cooling catastrophy.

Ref:

1.   1. Kopp RE, Kirschvink JL, Hillburn IA, Nash CZ.The Paleoproterozoic snowball Earth:A climate disaster triggered by the evolution of oxygenic photosynthesis. PNAS 2005;102:11131-11136

2.      2. Bar-On YM, Pholips R, Milo R. The biomass distribution on earth. PNAS 2018;115:6505-6511.

3.      3. Wikipedia for everything else as on 18.7.20