Tag: #evolution

Theories of Evolution – Darwinism

Charles Robert Darwin (1809-1882) was a British biologist, born on 12th February 1809 in Shrewberg, England. 

He presented his theory of evolution in the book On the Origin of Species by means of natural selection in 1859. Darwin argued that new species had evolved from older species, and he described the mechanism behind the transformation process. Darwin’s theory of evolution is based on the following five principles: 

  1. Organisms produce more offspring than can possibly survive.
  2. Organisms face a constant struggle to survive.
  3. Organisms within a species vary.
  4. Organisms best suited to their environment survive.
  5. Those organisms which survive will reproduce and pass on their genes to the next generation.

  • Over-production: All species have a tendency to produce more and more offspring in order to increase the population. For example, a salmon produces 28,000,000 eggs in a single season; a single spawning of an Oyster may yield as many as 114,000,000 eggs; a common roundworm lays about 70,000,000 eggs in a day. This huge production is to ensure the survival of the species. Even though species are produced in larger numbers, the population of a particular organism remains more or less constant.

  • Struggle for Existence: Darwin claimed that there was a continual ‘struggle for existence in nature, in which only the fittest would survive. As a result of overproduction, there is a struggle for existence among organisms. Since the number of is persons is large, there is competition for food, shelter, mates etc.

 struggle for existence may be of different types as follows: 

a. Intra-specific (Intra-species) struggle: The members of the same species struggle among themselves for food, shelter and mates. 

b. Inter-specific (Inter-species) struggle: The members of different species may go on fighting for survival. A member from one species may hunt other members of other species for food. 

c. Environmental struggle: Organisms of different species struggle against the environmental hazards like earthquake, flood, drought etc. Only those species with better adjustment with the environment will survive.

  • Variations: Variation is the tendency of an organism to deviate from the parental generation. These variations play a very important role for adaptations in the environment. Some variations are considered as favourable and others are unfavourable. Organisms with unfavourable variations easily get defeated in the struggle for survival. Variations that are useful to adapt to the pressures of the environment survive long. The new trait of advantageous characteristics is passed on to the future generations. 
  • Survival of the Fittest: The struggle for existence leads to the survival of the fittest. When there are too many of an organism in an area, they compete for resources such as food and perhaps shelter, for example trees and caves.The surviving species will reproduce more offspring than those who are less adaptive.
  • Natural Selection: The surviving individuals will give rise to the next generation. The successful variations are transmitted to the succeeding generations. The accumulation of advantageous traits in future generations gradually brings changes in species. Successive generations in this way tend to become better adapted to their environment. Eventually, a new species may evolve. 

Furthermore, certain members of a population with one group of variations may become adapted to the environment in one way, while others, with a different set of variations, become adapted in a different way or become adapted to different environments. In this way, two or more species may arise from a single ancestral stock. 

Examples of Natural Selection 

1. The finches of Galapagos : Some species of finches have short thick beaks. They are used to eating seeds, fruits and buds. Some others have long straight beaks. They subsist primarily on nectar from flowers. If environmental condition suddenly changes some characteristics may be more favoured than others. 

2. Industrial melanism in moth : Before Industrialisation, the tree trunks were lighter and light coloured moths were predominant. Dark coloured moths were also present but they were limited in number. As a result of industrialisation, the pollution resulted in the darkening of tree trunks. So the light coloured moths become more visible to birds and were therefore eaten by their predators. As a result of this at the end of 19th century the common light coloured moths were almost completely replaced by the black variety.

The theory of origin of species by natural selection is regarded as a major advancement in evolutionary thought. Darwin contributed to the modern understanding of biological evolution by documenting the variation of living forms and identifying the key process of natural selection.

 Like most 19th century scientists, however, he did not understand heredity or how specific traits are passed from one generation to the next. His theory lacked the knowledge of modern genetics. However, mutation theory explained the causes of variations among organisms.

Theories of Evolution – Lamarckism

The most important question that has always been exciting to human mind is about human origin and destination. Where did we come from and where are we heading to?

To understand the human origin and evolution, we have to first look in to the emergence of life on the earth. It is believed that life is originated from inorganic matters due to many physical-chemical conditions

Theories of Organic Evolution

The term evolution was first applied by the English philosopher Herbert Spencer, to mean the historic development in life. Evolution is a process that results inheritable changes in a population spread over many generations.

Lamarckism

Jean Baptist de Lamarck (1744-1829) was a French biologist. He spent the early part of his life as a botanist. Then at the age of 50, he turned his attention to zoology, particularly to the study of invertebrates. His extensive studies on invertebrates formed a base in zoological classification. As a result of his systematic studies, he became convinced that species were not constant but rather were derived from pre-existing ones. By consolidating all these ideas, he proposed his theory of evolution in his book Philosophie Zoologique 1809 which is known as Lamarckism.

Lamarck believed that organic changes seen in animals resulted from the influence of environment. According to him, when the environment changes, animals need to change their body structure as well. He proposed his ideas as two different laws as the following-


i) The law of use and disuse: A living body is influenced by environmental factors, and ultimately this phenomenon initiates an adaptation of organisms to their surroundings. As per the necessity, some parts of the body may be used more and more. Therefore, those parts tend to show more development or changes in the course of time, while the other parts of the body, which may not be required much, will become weak or degenerate due to constant disuse.

ii) Inheritance of acquired characters: Modifications produced during the lifetime of organisms become hereditary and will be inherited by the offspring. All the modifications that the organism acquires during its lifetime in adaptation to the environment are automatically transmitted to the next generation and so become a part of heredity

To support his theory, Lamarck presented several examples. The most remarkable one is associated with the long neck and tall front legs of giraffes. According to Lamarck, the ancestors of giraffe were normal animals with reasonably long neck and forelimbs. They depended on grass and bushy vegetation for their survival. But a sudden scarcity of leafy vegetation due to some environmental factors, forced the giraffe to depend on leaves of tall trees and for that they had to stretch their neck and forelimbs. The continuous stretching of these organs resulted in the long neck and long forelimbs of present day giraffe.

In another example, he mentioned that the ducks are unable to fly because their wings became weak, when they stopped flying. Again, the birds that started to live in an aquatic environment, gradually acquired webbed feet through the conquest of survival.

Criticism of Lamarckism

Lamarck’s theory has been criticised from many angles. The German scientist August Weismann criticised the essence of Lamarck’s theory of inheritance acquired characters by his experiments, which involved cutting off the tails of mice for over twenty-one generations. All tailless mice in all generations produced their offspring with tails. Therefore, he reached to the conclusion that the environmental factors might influence the body cells, but it is not enough to profess a change of reproductive cells. Characters of an organism would not be inherited unless the change could occur in the reproductive cells.

Characters of an organism would not be inherited unless the change could occur in the reproductive cells. According to Weismann the body of an animal is composed of two parts viz. germ plasm (germ cells) and somato plasm (body cells). Only those characters which are located in the germ plasm will be inherited.

As a result of these experiments, Lamarckian law of inheritance of acquired characters lost its evolutionary ground. But the effort towards finding facts related to organic evolution continued. Charles Darwin’s interest in this field gave birth to new findings (Darwinism).

The Upper Paleolithic World

Introduction

After about 40,000 years ago, we see many significant changes in the archaeological record, reflecting important changes in cultural and social life. We see art, many new inventions, and considerable increases in the population. This period of cultural history in Europe, the Near East, and Asia is known as the Upper Paleolithic and dates from about 40,000 years ago to the period known as the Neolithic (beginning about 10,000 years ago, depending on the area). In Africa, the cultural period comparable to the Upper Paleolithic is known as the Later Stone Age and many have begun much earlier.

In many respects, lifestyles during the Upper Paleolithic were similar to lifestyles before. People were still mainly hunters, gatherers, and fishers who probably lived in small mobile bands. They made their camps out in the open in skin-covered huts and in caves and rock shelters. And they continued to produce smaller and smaller stone tools.

But the Upper Paleolithic is also characterized by a variety of new developments. One of the most striking developments is the emergence of art – painting on cave walls and stone slabs, and carving tools, decorative objects, and personal ornaments out of bone, antler, shell and stone. (Perhaps for this, as well as other purposes, people began to obtain materials from distant sources.) Because more archaeological sites date from the Upper Paleolithic than from any previous period and some Upper Paleolithic sites seem larger than any before, many archaeologists think that the human population increased considerably during the Upper Paleolithic. And the new inventions, such as the bow and arrow, the spear thrower, and tiny replaceable blades that could be fitted into handles, appear for the first time.

The Last Ice Age

The Upper Paleolithic world had an environment very different from today’s. The earth was gripped by the last ice age, with glaciers covering Europe as far south as Berlin and Warsaw, and North America as far south as Chicago. To the south of these glacial fronts was a tundra zone extending in Europe to the Alps and in North America to the Ozarks, Appalachians, and well out onto the Great Plains. Environmentally, both Europe and North America probably resembled contemporary Siberia and northern Canada. Elsewhere in the world conditions were not as extreme but were still different from conditions today.

For one thing, the climate was different. Annual temperatures were as much as 50 °F below today’s, and changes in ocean currents would have made temperature contrasts (i.e., the differences between summer and winter months) more extreme. The changing ocean currents also changed weather patterns, and Europe experienced heavy annual snowfall. Not all the world was cold, however; still, the presence of huge ice sheets in the north changed the climate throughout the world. North Africa, for example, appears to have been much wetter than today, and South Asia was apparently drier. And everywhere the climate seems to have been highly variable.

Upper Paleolithic Europe

With the vast supplies of meat available from megafauna, it is not surprising that many Upper Paleolithic cultures relied on hunting, and this was particularly true of the Upper Paleolithic people of Europe, on whom we focus here. Their way of life represents a small pattern throughout the Old World. But as people began to use more diverse resources in their environments, the use of local resources allowed Upper Paleolithic groups in much of the Old World to become more sedentary than their predecessors. They also began to trade with neighbouring groups to obtain resources not available in their local territories.

Reference : Anthropology by Ember and Ember

HUMAN EVOLUTION

The story of human origins is complicated since our ancestors swapped genes (and probably skills).

The first humans emerged in Africa around two million years ago, long before the modern humans known as Homo sapiens appeared on the same continent.

There’s a lot anthropologists still don’t know about how different groups of humans interacted and mated with each other over this long stretch of prehistory. Thanks to new archaeological and genealogical research, they’re starting to fill in some of the blanks.

The First Humans

Homo habilis individuals chip away at rocks, sharpening them for cutting up game or scraping hides while a woman, with her child, gathers wild berries to eat and branches to make shelters.

First things first: A “human” is anyone who belongs to the genus Homo (Latin for “man”). Scientists still don’t know exactly when or how the first humans evolved, but they’ve identified a few of the oldest ones.

One of the earliest known humans is Homo habilis, or “handy man,” who lived about 2.4 million to 1.4 million years ago in Eastern and Southern Africa. Others include Homo rudolfensis, who lived in Eastern Africa about 1.9 million to 1.8 million years ago (its name comes from its discovery in East Rudolph, Kenya); and Homo erectus, the “upright man” who ranged from Southern Africa all the way to modern-day China and Indonesia from about 1.89 million to 110,000 years ago.

In addition to these early humans, researchers have found evidence of an unknown “superarchaic” group that separated from other humans in Africa around two million years ago. These superarchaic humans mated with the ancestors of Neanderthals and Denisovans, according to a paper published in Science Advances in February 2020. This marks the earliest known instance of human groups mating with each other—something we know happened a lot more later on.

After the superarchaic humans came the archaic ones: Neanderthals, Denisovans and other human groups that no longer exist.

Archaeologists have known about Neanderthals, or Homo neanderthalensis, since the 19th century, but only discovered Denisovans in 2008 (the group is so new it doesn’t have a scientific name yet). Since then, researchers have discovered Neanderthals and Denisovans not only mated with each other, they also mated with modern humans.

“When the Max Plank Institute [for Evolutionary Anthropology] began getting nuclear DNA sequenced data from Neanderthals, then it became very clear very quickly that modern humans carried some Neanderthal DNA,” says Alan R. Rogers, a professor of anthropology and biology at the University of Utah and lead author of the Science Advances paper. “That was a real turning point… It became widely accepted very quickly after that.”

As a more recently-discovered group, we have far less information on Denisovans than Neanderthals. But archaeologists have found evidence that they lived and mated with Neanderthals in Siberia for around 100,000 years. The most direct evidence of this is the recent discovery of a 13-year-old girl who lived in that cave about 90,000 years ago. DNA analysis revealed that her mother was a Neanderthal and her father was a Denisovan.

The human lineage of Australopithecus afarensis, Homo habilis, Homo erectus, Neanderthals and Homo sapiens.

Scientists are still figuring out when all this inter-group mating took place. Modern humans may have mated with Neanderthals after migrating out of Africa and into Europe and Asia around 70,000 years ago. Apparently, this was no one-night stand—research suggests there were multiple encounters between Neanderthals and modern humans.

Less is known about the Denisovans and their movements, but research suggests modern humans mated with them in Asia and Australia between 50,000 and 15,000 years ago.

Until recently, some researchers assumed people of African descent didn’t have Neanderthal ancestry because their predecessors didn’t leave Africa to meet the Neanderthals in Europe and Asia. But in January 2020, a paper in Cell upended that narrative by reporting that modern populations across Africa also carry a significant amount of Neanderthal DNA. Researchers suggest this could be the result of modern humans migrating back into Africa over the past 20,000 years after mating with Neanderthals in Europe and Asia.

Given these types of discoveries, it may be better to think about human evolution as a “braided stream,” rather than a “classical tree of evolution,” says Andrew C. Sorensen, a postdoctoral researcher in archaeology at Leiden University in the Netherlands. Although the majority of modern humans’ DNA still comes from a group that developed in Africa (Neanderthal and Deniosovan DNA accounts for only a small percentage of our genes), new discoveries about inter-group mating have complicated our view of human evolution.

“It seems like the more DNA evidence that we get—every question that gets answered, five more pop up,” he says. “So it’s a bit of an evolutionary wack-a-mole.”

Early Human Ancestors Shared Skills

Human groups that encountered each other probably swapped more than just genes, too. Neanderthals living in modern-day France roughly 50,000 years ago knew how to start a fire, according to a 2018 Nature paper on which Sorensen was the lead author. Fire-starting is a key skill that different human groups could have passed along to each other—possibly even one that Neanderthals taught to some modern humans.

“These early human groups, they really got around,” Sorensen says. “These people just move around so much that it’s very difficult to tease out these relationships.” 

Origin And Evolution Of Man

About 15mya, primates called Dryopithecus and Ramapithecus were existing. They were hairy and walked like gorillas and chimpanzees.

Ramapithecus was more man-like while Dryopithecus was more ape-like. Few fossils of man-like bones have been discovered in Ethiopia and Tanzania.

These revealed hominid features leading to the belief that about 3-4mya, man-like primates walked in eastern Africa. They were probably not taller than 4 feet but walked up right.

Two mya, Australopithecus probably lived in East African grasslands. Evidence shows they hunter with stone weapons but essentially ate fruit.

Some of the bones among the bones discovered were different. This creature was called the first human-like being the hominid and was called Homo habilis.

The brain capacities were between 650-800cc. They probably did not eat meat. Fossils discovered in Java in 1891 revealed the next stage, i.e., Homo erectus about 1.5mya.

” Homo erectus had a large brain around 900cc. Homo erectus probably ate meat. The Neanderthal man with a brain size of 1400cc lived in near East and Central Asia between 1,00,000-40,000 years back. They used hides to protect their body and buried their dead.”

Homo sapiens arose in Africa and moved across continents and developed into distinct races. During ice age between 75,000-10,000 years ago modern Homo sapiens arose.

Pre-historic cave art developed about 18,000 years ago. Agriculture came around 10,000 years back and human settlements started. The rest of what happened is part of human history of growth and decline of civilisations.

https://www.britannica.com/science/human-evolution

https://www.yourgenome.org/stories/evolution-of-modern-humans

Adaptive Radiation

The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called Adaptive Radiation.

Evolution of the Finches

During his journey Darwin went to Galapagos Islands. There he observed an amazing diversity of creatures. Small black birds later called Darwin’s Finches amazed him. He realised that there were varieties of finches in the same island.

From the original seed-eating features , many evolved on the island itself. From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches. This process is called adaptive radiation.

“The principle of adaptationism has been adopted so widely by Darwinians because it is such a heuristic methodology.”

“Adaptive radiation refers to the adaptation (via genetic mutation) of an organism which enables it to successfully spread, or radiate, into other environments.”

Adaptive radiation of marsupials

Darwin’s finches represent one of the best examples of this phenomenon. Another example if Australian marsupials. A number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent.

When more than one adaptive radiation appeared to have occurred in an isolated geographical area( representing different habitats) , one can call this convergent evolution.

Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be ‘similar’ to a corresponding marsupial.

“Speciation is the development of one of multiple new species in the evolutionary process, where the original species produces mutated forms which successfully survive in other environments due to these mutations.”

“Phylogenetics is the study of the evolutionary steps a species has taken during the process of speciation.”

https://biologydictionary.net/adaptive-radiation/

https://www.sparknotes.com/biology/evolution/speciation/section3/

Evolution

When you think of evolution the first name that comes to one’s mind is that of Charles Darwin. However, the fact is that he was not the first person to put forward the idea of evolution. Lamarck had suggested it earlier but the concept was not popular. In fact zoology professor Robert Grant lost his job because he supported Lamarck theory! An anonymous work titled, ‘The Vestiges of creation’ was ridiculed. It was Charles Darwin who first made the theory acceptable and he was able to do so because he supported it with a huge amount of evidence. Darwin, an English naturalist put forward his theory in a book titled ‘On the origin of the species’. He established that all species descended from common ancestors and that the different species evolved through a process he called natural selection. Darwin’s theory gained acceptance because it was able to explain the diversity of life.


Ramapithecus belongs to an extent group of primates that lived from about 12 to 14 million years ago. Fossils of Ramapithecus were discovered in India and Africa beginning in 1932. Fossil evidence suggested that it had a short face, heavy jaws and enamelled teeth like hominids. Its importance lies in the fact that it was regarded as a possible ancestor of Australopithecus and therefore of modern humans. Later for sale finds indicated that Ramapithecus was more closely related to the orangutan and Ramapithecus is now regarded by many as a member of a group known as Sivapithecus.


It has been long known that humans share a common ancestor with apes but it was only in the last 30 years that techniques for develop to provide strong evidence in support of the theory that humans are more closely related to chimpanzees than they are to gorillas orangutans or Gibbons. The DNA of a chimpanzee is 98% identical to that of a human being. However our bodies adapted for walking on 2 legs. This is possible because the lower portion of the human body evolved to facilitate load bearing and balancing while walking upright. Chimpanzees not only share most of our genes they seem to be able to handle tools and they are able to grasp language pretty well too. Now researchers have found that we share a similar brain pattern when communicating. But in spite of these similarities there are clear differences in body structure intellect and behaviour.


Australopithecus was an early hominid which is now extinct. Fossil evidence suggests that these individuals lived from approximately 4- 2 million years ago after evolving on the continent of Africa. Sense the fossils were recovered from south Africa they were called south African man apes or australopithecines. Australopithecines are believed to have been around 1 to 1.5 metre tall and probably fed on leaves fruits and the remaining of dead animals. Their brains were larger than those of apes but smaller than human brains while their teeth would like human teeth it is believed that Australopithecus eventually evolved into modern humans.


Neanderthal man first appeared in Africa about 200,000 years ago and migrated to the rest of the world around 100,000 years ago. The name Neanderthal comes from Neander valley where an early skull was found. Neanderthals would different from other species of early man. They were much taller and very strong for stop the brains were actually larger than ours are today. They were marvellous hunters. They often used caves as their homes. They were adept at fire making and probably cooked their food routinely. Neanderthals buried their dead. The Neanderthals died out by around 30,000 BC.
Cro-Magnon man lived some 40,000 -10,000 years ago. Their remains were first found in France in 1868 and then throughout other parts of Europe.

Cro-Magnon man was anatomically identical to modern humans and deferred significantly from Neanderthal man who disappeared in the fossil record shortly after Cro-Magnons appearance. Cromagnon man was tall and had an erect posture. He had a prominent chin a surprising forehead and skull shaped like hours. These man was killed hunters toolmakers and artists. Cro-Magnon man was a true human and looked just like us. He is represented by the remains of 5 individuals found in March 18683 adult males one adult female and one child.


•First family.
In 1975 Donald Johansson discovered the remains of at least 13 individuals of all ages at her there in Ethiopia. The sizes of the specimens varied greatly and Johansson believed that they all belong to a single species Australopithecus afarensis in which men were much larger than the females.

Thank you for reading. Have a nice day!🌼

Chocolate and its Evolution

Chocolate is a sweet brown food preparation of roasted and ground cacao
seeds that is made in the form of liquid, paste or in a block or used as a flavoring ingredient in other foods .The word ‘Chocolate’ is the Aztec word, ‘Xocolatl’, which means ‘Bitter Water’.Theobroma cacao is the scientific name of the tropical tree that bears the fruit whose name means the ‘food of he gods’.

The Brief history behind chocoloate

Before the 16th century chocolate existed in mesoamerica. The first
people to use chocolate were probably known as Olmec of what is today southeast Mexico. They lived in the area around 1000 BC where the cacao trees grew
wild. It is not yet known if the Olmecs actually used chocolate.However the Maya who inhabited the same general area a thousand years later did use chocolate. The Mayans used the cacao beans as currency. Even after
counterfeits were made by carving clay, the beans were still used as currency in parts of Latin America until the 19th century. The Mayans also used chocolate in religious rituals. They were also
used in marriage ceremonies and baptism. They even had a cacao god. But the Mayans prepared chocolate strictly for drinking. Only the rich
could afford this luxury. Emperors were often buried with jars of chocolate at their side.After the Aztecs overthrew the Mayas they kept the chocolate tradition
alive. The Aztecs dominated the region and continued using cacao as currency. Soon after the Spanish conquest of the Aztecs, chocolate was imported to Europe.

How did chocolate become so popular?

The Spanish initially did not like the bitter taste of chocolate but imported it back
to Europe. It was therefore initially used as medicine to cure abdominal pain . By the 1590s chocolate was mixed with honey, vanilla, and sugar, giving it a much
sweeter taste. Initially chocolate was considered sinful by some members of the church as some
drank it to divert themselves from a long service. This changed as the elite and
noblemen supported its consumption. However chocolate always remained a drink.
After the introduction of industrialization, entrepreneurs began experimenting
with different machinery to facilitate the process of separating cacao butter from
cacao seeds. Soon cacao powder was produced and chocolate now became more mass
produced. However it was still a product for the upper class.

Who first invented chocolate

The creation of the first modern chocolate was by Joseph Fry who
discovered in 1847 that he could make a mold able chocolate paste by
adding melted cacao butter into Dutch cacao.It was by 1868 a little company called Cadbury was marketing boxes
of chocolate candies in England. Milk chocolate hit the market a few
years later pioneered by another name – Nestle. By the 19th century chocolate became a mass produced.

Types of chocolates

Chocolate Liquor : Its referred to as unsweetened chocolate and is the
base of all types of chocolate. This thick dark brown paste is created from
cacao nibs, the inside of the cacao beans. Despite the name it doesn’t
contain alcohol.
● White chocolate : It is made by combining sugar, cacao butter, milk,
vanilla, and an emulsifier (lecithin).
● Milk chocolate : It is made by combining chocolate liquor, sugar and milk.
Sometimes emulsifiers are added for smoothness.
● Dark chocolate : It is referred to as black or semisweet and made of
chocolate liquor and sugar.
● Bittersweet chocolate : It is often referred to as extra dark chocolate.
● Ruby chocolate : This chocolate has a hot-pink hue as it derives colour
from a specific type of cacao. It gives a taste of fruitiness and sour taste.

How did we evolve?

Historical sources are pretty difficult to find. Why? Because, we never know where exactly they are, are they even real. It solely depends upon. Our imagination. Cause we can’t grab a time machine and time travel to see exactly what happened (but that would’ve damn great!). Evolution is crucial in every animal and has taken place eat one point of time. But then..who were we evolved from..?

  • The starting point

Now, atleast at some point of time,you must have thought, ‘From where the heck did this universe start?’.  The thing is, We Don’t Know. We do have theories regarding the point though, which give an applicable reason as to the beginning of life. So the theory was of the Big Bang. We all know what exactly this ‘big bang’ is.It is believed that, there existed something very small,smaller than any other thing. Even from a microbe.And at one point,it exploded. That phenomenon was called the big bang, through which large balls of fire were generated. After many billions of years,the fire balls started to align themselves, unto a newly forming star,the Sun due to its pull. And eventually,some more billion years later,the fireballs started to cool down. Now,was the time when the first organism appeared on earth. But why only earth. Because, Earth is situated in something called the ‘Goldilocks zone’. The earth was just at a perfect distance from the sun for life to exist. If the earth was any nearer of any farther, you and me, including everything would probably not have existed at all.(sad? I know). The first organism to exist on earth was the Archaea.  This microbe was the first to live on the still hot earth. How? Archaea, maybe   had adapted themselves to the hot temperatures of the earth. Which means, we all have actually evolved from Archaea!

They are even found today, in the thermal beds, and wherever the temperatures are fit for them.

From the Archaea evolved the bacteria, which are prokaryotes(primitive organisms) then came the eukaryotes(  true cells) and all the kingdoms. And today we live with all the complex tissues and cells, working everyday in our bodies. How did water come though? It is believed that during the big bang, not only did it release fireballs,but also many gases. Then, probably the atoms of hydrogen(H) and Oxygen (O)  made bonds to create the existence of water. These are all one of the speculations and assumptions made by us to understand the beginning of life in a better way. Who knows the truth? No one does. At least not from earth anyways.

Photo By Pixabey

Even now the earth is still cooling down. A live example would be volcanoes. Meaning,only the outer portion of earth has cooled down after the time period of 4.5 billion years. So,when the water made an appearance on the surface of earth, seas and oceans were probably formed. But the lands were still not. Then where did life continue to exist?In the oceans of course. Something called the Endo-genetic movements ( movements which occur on the inside of the earth) made the continent buildings possible.

While the continents still continued to cool down, after the volcanic eruption that is, the life in the aquatic region continued to make  progress.

Did you know that the continents which are formed today are not how it was a million years ago?

 Many types of continental structures were formed in our history. For example: Rodinia,Pannotia, Pangaea, Gondwana etc. Out of these, Pangaea lasted for the longest period.( due to the internal and external movements of earth,the continental formation kept on changing). How did Dinosaurs go extinct? Dinosaurs came to extinction due the humongous amounts of volcanic eruptions and the other Endo-genetic movements( yes,those cartoons had shown you the truth!)

Photo by Clive Kim from Pexels

Now what happened was that the living organisms which were living in the aquatic region came to the land. Slowly,they started adapting themselves to the terrestrial lands. They say that evolution of man,that is the ancestors of our species are from apes. Slowly but steadily,they evolved to form stages. The first stage was said to be Homo Habilis,the second was Homo Erectus, the third was Neanderthals, and then finally,the Homo Sapiens. Infact, all of these species used to live together. Meaning,suppose it was not like everyone was Neanderthals, some of them were still not evolved from Homo Erectus. They all lived and learnt the sources of nature. 

As time passed, they evolved, their organs developed and were also divided. But….wait! Does that mean that we evolved from oceans? Well, we don’t exactly know about the truth but it is said that the statement does hold some weight on it and might be true. And if it was true, we had gills for lungs! Infact, some people say that we did evolve from the oceans. How? Because,the person who held most maximum time in water is 20 minutes. The same amount the dolphins can hold their breath in water. We don’t have any specific organ to conserve our sweat but the other animals do. We have fingerprints  and footprints instead of paws. Sure,these statements may be irrational to many people,but it lets one to imagine. To brainstorm about where exactly did we,as in our existence start from?

Fact- It is believed that hiccups are the left out defect of our aquatic habitat….….is it true,though? Nobody knows so!

The Organic Evolution: How Did The Current Biodiversity Reached Its Present Form

We see the actual spirit of diversity in Nature.But have things always been like this, barring a few minor change-in-scenes, since times immemorial? If not, how did and how much has life forms changed? So, let’s find out from where all this started.

The Beginning: Life on Earth

After formation, Earth was not exactly suitable for housing or nurturing any kind of organisms. After undergoing drastic changes -including solidification of crust, formation and accumulation of various gases (like nitrogen,ammonia,methane,oxygen,hydrogen etc.) in the atmosphere, gradual development of ozone layer and formation of water molecules- Earth became close to be able to support even the most basic forms of ‘life’.

The earliest organic forms, though did not really satisfy our definition of life, but are considered to be the most basic forms of living cells.Experiments by Stanley Miller (1953), Sidney Fox and Oparin (1936), gave the world some theories about the formation of living organisms. Another mention worthy point is that the first life forms originated in water, as for the longest time, Earth was what we can imagine as a giant sea, with no signs of land whatsoever. These organic forms might have developed into self replicating units, then into primitive organisms and at later stages, resulted into some distinct type of chlorophyll synthesizing bacteria, some 2.5-2.3 billion years ago. This gradual process of arising of life from non-living matter (such as simple organic compounds) is termed as abiogenesis.

Evolution of chlorophyll occured around 600 million years ago. With that, the production of oxygen and ozone (after chemical conversion under suitable circumstances) sped up and gradually accumulated in the atmosphere. Ozone layering encased the surface of Earth and provided protection against UV rays, which is detrimental for living organisms. Before that, all organisms developed in deep water, which provided protection against the UV rays. Only after the formation of ozone layer did life flourished on land surface.

The Precambrian age, that last from 4600 to 542 million years old, has very few fossil records. Hence, such a large period of time is not subdivided into further categories in terms of biological evolution. The fossil of this period mainly of cellular organisms.The first living organisms are believed to have developed around 3.8-3.6 billion years ago, from the primitive organic soup (accumulation of large number of complex organic molecule assemblages). Around 3.5 billion years ago,first organisms with prokaryotic cells (cells without true nucleus and having a rudimentary cell structure) are believed to have developed. Those cells were at similar cell complexity level like the present day bacteria.Skip to 2.4 billion years later, the eukaryotic cells are supposed to have developed. For the longest period of time, only unicellular life forms flourished on Earth. Then,evidences indicated that, around 700 million years ago, the first signs of multicellular organisms were traced. Since then, there has been a steady flow of evolution. 

The ‘Complex’ Evolution

The Cambrian period (542- 488.3 million years) is considered to be a milestone in evolution. Even the fossils have records from around 600 million years ago. It is widely assumed that around 600 million years ago, organisms had developed to be able to leave fossilized records. The transition of life forms from water to land had supposedly begun around 500 million years, when plants started growing on land.Later different varieties of plants and animals populated the lands.

The Carboniferous period was an important landmark, which lasted from about 359 to 299 million years in the past, is an important landmark in the journey of evolutionary history. The environ domain was actively dynamic during that period. Humid and warm climate, swampy large areas, changes in sea levels, flood, mud and sand were deposited over the vegetations, etc.

Due to compaction and incomplete decomposition of  plant material in swamps, they converted into peat bogs, and then, into coal. Hence the name carboniferous. In the late Carboniferous period (about 300 million years) tropical rainforests were present in the equator region of Euramerica. Later, ferns replaced the forests, which are present even today.These vascular plants are without seeds as they do not produce flowers and fruits, and are generally found in temperate to tropical parts of Earth. These plants can be mainly divided into stem, leaves and true root; reproduction being facilitated through special structures, known as sporangia (singular:sporangium), that contain spores, which are dispersed into different mediums and germinates on coming in contact with the soil with suitable conditions.

Next period in the geological time scale in the Permian period, which started off around 299 million years ago. This period witnessed major altering activities in the continental lithosphere (which are broken into tectonic plates) starting from the joining of Euramerica, Asia and Gondwana led to the formation of a single landmass called Pangea (Greek translation: All lands), which is considered to be a supercontinent. In terms of ecology, this period was mainly dominated by forests of conifers and tree ferns,large amphibians and reptiles habituating them, and a huge variety of fish and shellfish in the ocean. But, at the end of Permian period, a mass extinction took place, commonly referred to as the ‘Great Dying’. It occured around around 252 million years ago, and wiped out about 90% of all the species present on Earth.Also, trilobites (meaning: three lobes), which a group of arthropod (a group of invertebrate animals with exoskeleton, segmented body, and appendages) and sea scorpions, which had survived the tides of oceans and time for hundreds of million of years, went extinct. 

Next in the line, the Triassic period had set off around 240 million years ago.It is believed that true mammals first evolved during this period, more precisely, during late Triassic period. Also, a specialized subgroup of  Therapsids, which is a group of reptile-like animals that included mammals and their ancestors, also evolved. Early Therapsids demonstrated traits of the present day mammals, such as erect posture. First flying vertebrate animals are supposed to have originated around 215 million years ago, and lasted for 150 million years, vanishing at the end of the Cretaceous period. Another mention worthy occurence in the Triassic period timeline is the splitting of Pangea into two separate land masses. The northern one was named Laurasia and the southern one, Gondwana. Primitive forms of dinosaurs are said to have emerged around 231.4 million years ago.

The Jurassic period is known as the ‘Age of Reptiles’, as they were present in abundance and had a diverse variation throughout this period. The land animals included Stegosaurus, Ceratosaurus, Brachiosaurus and Allosaurus. The oceans were traversed by Ichthyosaurus and Plesiosaurus and the skies are believed to be dominated by the likes of Rhamphorhynchus and Archeopteryx. This period coincided with the emergence of first mammals and birds.

 The Cretaceous period, which started around 145 million years ago, is geologically characterized by separation of India from Gondwanaland, formation of Andes and Rocky mountains, and extensive volcanic activities. Dinosaurs dominated the face of Earth and were of different types. They lived through a period of 135 million years, that is , throughout the Jurassic and Createceuos period. The Cretaceous-Paleogene mass extinction is considered to be the main cause of dinosaurs disappearing from Earth. An important claim by the scientists, on the basis of fossil records, is that the birds evolved from the Theropod dinosaurs, and the development took place in the Jurassic period. Some birds lived through the extinction and their descendents continue to live presently. This period also marks the appearance of angiosperms; plants that could produce flowers. 

Next chapter

The next major development in the course of evolution is considered to be the evolution of humans. But that’s a story for another day. As for our evolution is anything but simple and short. As Carlo Rovelli said in his book, Seven Brief Lesson of Physics: “We are a species which is naturally moved by curiosity, the only one left of a group of species (the genus Homo) made up of a dozen equally curious species. The other species in the group have already become extinct; some, like the Neanderthals, quite recently, roughly thirty thousand years ago. It is a group of species which evolved in Africa, akin to the hierarchical and quarrelsome chimpanzees — and even more closely akin to the bonobos, the small, peaceful, cheerfully egalitarian and promiscuous type of chimps. A group of species which repeatedly went out of Africa in order to explore new worlds, and went far: as far, eventually, as Patagonia — and as far, eventually, as the moon.

It is not against our nature to be curious: it is in our nature to be so.”

Website References

https://en.wikipedia.org/wiki/Abiogenesis

https://www.goodreads.com/quotes/9344668-we-are-a-species-which-is-naturally-moved-by-curiosity

Bibliography

Extinctions: No Comebacks by M.A. Haque

Mass Extinctions: The Troughs of Biological Evolutionary History

With 2020 turning out to be a very abysmal year, complete with natural disasters and pandemic, I’m positive that many of us, at some point in time, have heard, seen or shared jokes about how the ‘end’ is approaching. Though it doesn’t intimidate our dear Earth,as it already has some experience in witnessing the wiping out of most of the life forms, then, in habitation. Infact, this occurrence, known as mass extinction, has been a part of evolutionary history for several times. So, now the question arises; who, when, how and also, how many times? Let’s find out.

Introduction

Earth is believed to be approximately 4 billion years old, which gives ample time to geological and biological evolution. The compilation of all those changes and evolutions structure the present day Earth, aside the anthropogenic modifications. And some of the major events of the evolutionary history of Earth are mass extinction. That’s right. Even the destruction of species after species has contributed to the shaping of Earth’s present. 

The Catastrophes: Mass Extinction

Extinction is a natural phenomenon that takes place due to changes in the environment. Complete disappearance of a species is its extinction. A species is a group of organisms with similar biological, physiological and anatomical characteristics and which can interbreed and produce fertile offspring. The species which cannot adapt with the environmental changes, cannot evolve with subsequent reproduction or cannot reproduce fast enough to keep up with the decline of their population, perish and become extinct. 

A typical species becomes extinct within 10 million years of its first appearance. It is estimated that 99.9% of all species that ever habituated Earth are now extinct.

Mass extinction is referred to as the event which results in the simultaneous extinction of a large number of species present on Earth. These events resulted in severe reduction in the number of organisms in a short amount of time and also decreased the speciation. Hence, the rate of reproduction slowed down, and eventually led to the extinction. It is identified by sharp change in diversity and abundance of organisms.

Mass extinction has some special characteristics:.

  • It took place over a short span of time and were quite intense
  • It was a global phenomenon and included a large diversity of organisms
  • Extinctions were believed to be more severe in case of marine organisms
  • It is considered that plant species are more resistant to extinction than animals.

Mass extinction evidences can be found in fossils trapped in rocks and rock layers, which had been deposited on Earth’s surface for billions of years. On the basis of the incomplete fossil records, 5 major mass extinctions have been identified. In the descending order of age, they are:

  1. Ordovician- Silurian Mass Extinction/Late Ordovician Mass Extinction (450-440 million years ago) at Ordovician-Silurian transition

In May 2020, studies suggested that due to global warming, caused mainly due to volcanism and anoxia, killed off 27% of all families, 57% of all genera and 60%-70% of all the species.49-60% of marine genera and nearly 85% of marine species were eliminated. There were two main causal events. In terms of percentage of genera becoming extinct, these are regarded as the second largest of the five major extinctions.

The LOME is considered to have occurred in two distinct pulses, one at the boundary of the between Katian and Hirnantian stages of the Late Ordovician Period. The second pulse occurred in the later half of the Hirnantian stage, and is associated with intense worldwide anoxia(oxygen depletion) and euxinia (toxic sulfide production), persisting through the Rhuddanian age of Silurian period.

The other plausible causes that were/are debated are glaciation, toxic metal poisoning, gamma-ray burst and weathering

  1. Late Devonian Mass Extinction (375-364 million years ago) near the Devonian- Carboniferous transition

A prolong series of extinction resulted in elimination of 19%of all families, 50% of all genera and at least 70% of all species. It might have lasted for as long as 20 million years.The beginning and end of this period is marked by Kellwasser event and Hangenberg event respectively. According to Late Devonian sedimentary records, it was a period of several environmental changes, which might have directly affected biodiversity and caused extinction. Evidence of rate of carbon burial shooting up and widespread anoxia at ocean bottoms have been discovered. Possible triggers of these changes are:

  • Asteroid impact 
  • Supernovae event, which lead to drastic drop in atmospheric ozone ultimately resulting in genetic material damage due to UV rays.
  • Plant evolution and expansion
  • Weathering due to plant evolution, which caused drastic changes in nutrients cycles. That, in turn, led to deposition of surplus nutrients in water bodies, leading to eutrophication and subsequent anoxia.
  • Reduction of atmospheric carbon dioxide, again due to evolution of plants
  • Magmatism
  1. Permian Triassic Mass Extinction/ Great Dying (252 million years ago) at Permian-Triassic transition

It is considered to be the most severe extinction in the evolutionary history of Earth. About 96% of all marine species and 70% of terrestrial vertebrates went extinct. In case of insects, 57% of all biological families and 83% of all genera faced extinction.

Evidence of about 1 to 3 pulses/phases of extinction are identified. The potential causes that had been identified include:

  • Meteor impact event(s)
  • Massive volcanic eruptions
  • Climate changes due to large production of methane
  • Sea level changes
  • Increasing anoxia
  • Increasing aridity
  • Hydrogen sulfide emission
  1. End Triassic Mass Extinction (201 million years ago) at Triassic-Jurassic transition

 In marine biodiversity, a whole class(conodonts) and 23-24% genera went extinct. The terrestrial organisms which suffered extinction include archosauromorphs (excluding crocodylomorphs, pterosaurs) and some dinosaurs went extinct. Groups like aetosaurs, phytosaurs etc., which were previously abundant, went extinct. The Jurassic age saw a diverse evolution of dinosaurs and  pterosaurs.

The possible causes of this mass extinction include:

  • Gradual climate change, sea-level fluctuations or a pulse of oceanic acidification, decreasing diversity of land biomes
  • Trend of increasing aridification
  • Drop in sea level
  • Extraterrestrial causes; includes impact from an asteroid or comet
  • Volcanic eruptions
  1. Cretaceous Tertiary Mass Extinction (65 million years ago) at Cretaceous-Paleogene transition 

This extinction is responsible for about 80% of all species of animals, including all the dinosaurs and many marine invertebrates. It also includes a range of fishes, mammals,pterosaurs and plesiosaurs, amongst other groups of animals. The main trigger for this extinction is considered to be asteroid impacts. This period recorded several large asteroid impacts.This hypothesis is further solidified by unusually high levels of iridium in the rocks of that period, which is usually not available on the surface of earth. 

As the after effect of this extinction,’impact winter’ was set into motion. Due to all the ash, dust and other matter that were dispersed in the atmosphere due to the asteroid impacts, blocked out sunlight for a long period of time.As a result, plants could not effectively perform photosynthesis, and keep up the oxygen level in the atmosphere. It also resulted in shortage of food for animals. The worst hit animals were the dinosaurs, due to their massive size.The smaller animals, on the other hand, strived with storage food and lesser oxygen, and thrived after the danger passed.Other calamities induced were tsunamis, earthquakes and increased volcanic activities.

Apart from these, scientists have identified several other minor extinctions, with the help of fossil and petrological records. 

Holocene Extinction: Living through History

At present, we are living through an extinction referred to as Holocene extinction or Anthropocene Extinction, which is considered to be the sixth major mass extinction. It is, needless to say, majorly a result of human activities. The current rate of extinction of species is 100 to 1000 times higher than the natural rate of extinction. The direct causes include hunting, deforestation, pollution, introduction of non native species in various diverse geographical regions etc.

If this doesn’t give mankind the wakeup call that it direly needs, I don’t know what would.

Websites referred:

https://en.m.wikipedia.org/wiki/Extinction_event

https://en.m.wikipedia.org/wiki/Holocene_extinction