The Accidental Evolution of Homo sapiens: How Extinctions and Chance Shaped Life On Earth

The history of life on earth is littered with evolutionary mistakes, natural disasters and mass extinctions.

It is thought by some that human beings are the pinnacle of creation, an example of evolutionary perfection that was an inevitable consequence of the development of life. In reality, this view couldn’t be further from the truth.

Human beings are no more and no less evolved than any other species on earth. Homo sapiens have evolved to cope with certain environments and perform particular tasks. A bat, for example, is just as evolved, but has developed to live in a very different environment.

Accidental Development of Species

If all life on Earth became extinct tomorrow and the whole evolutionary process began again, Homo sapiens would not eventually re-evolve in several billion years time. There have been literally trillions of accidental events that led to the existence of all current life on the planet.

Take, for example, the mass extinction of the dinosaurs, 65 million years ago. It is now accepted by scientists that this event was caused by the impact of a meteor, in what is today the Gulf of Mexico.

Up until this point, the ancient ancestor of Homo sapiens was a small, shrew-like mammal that generally kept a low profile in the shadow of its larger reptilian cousins. It was not until the dinosaur population was decimated, that the mammals could evolve into new areas and start on the path to humanity.

Other mass extinctions are also known to science. These too shaped the future state of all life on Earth.

The Role of Chance Extinction

Beyond natural catastrophes such as meteor impacts and ice ages, many other chance factors have shaped life on Earth. One mechanism of evolution is mutation. This is where mistakes appear in the genetic code of an organism, and this alteration leads to some form of physical difference.

The vast majority of mutations are either harmful or have no effect at all. Some, however, are beneficial. This benefit leads the organism to have a better chance of survival, and consequently reproduce more. This beneficial mutation is then passed on to the next generation, which also have an increased chance of survival.

The key point here is that mutation is random. Human beings have well developed eyes thanks to a series of chance mutations, but those mutations were haphazard. Evolution does not plan for the future, and so if an immediate advantage is less than a perfect design, so be it. This has led to Homo sapiens having a blind spot, the area on the retina where the optic nerve enters the eye. Other animals, for example some squid, do not have a blind spot. This is purely down to chance mutation.

The fact that through hundreds of millions of years of extinction, mutation, suffering and pain, Homo sapiens exist is something amazing that shouldn’t be underestimated. For billions of years, life on earth had no need for the level of intelligence that leads to civilisation, and if humanity disappeared tomorrow, it may never happen again.

This underscores the importance of protecting the planet and life on earth, to make sure that the incredible series of chance of events that have brought humanity to this point was all worth it.…

DNA Paternity Testing – RFLPs: Restriction Fragment Analysis of a Genome

What Is a Paternity Test?

Before we were able to analyze DNA, blood tests were used to assess paternity. However, blood testing is limited, in that it can only rule out a possible father, not prove paternal identity.

Today, genetic technology is used, and DNA paternity testing makes it possible to, with a very high degree of certainty, determine the identity of a child’s biological father.

The Genetic Code

Everyone, except identical twins, has a unique set of genetic instructions made of DNA (deoxyribonucleic acid). DNA is a nucleic acid made of smaller molecules called nucleotide monomers, and each nucleotide is made of the same general ingredients:

  • a pentose sugar
  • one or more phosphate groups
  • a cyclic nitrogenous base

The specific nitrogenous base is what makes one nucleotide differ from another, and nucleotides of DNA each contain one of four possible nitrogenous bases:

  • Adenine (A)
  • Cytosine (C)
  • Guanine (G)
  • Thymine (T)

These four bases, particularly the combination in which they exist in along the DNA molecule, form the ‘genetic code’.

Restriction Fragment Analysis

Also called DNA fingerprinting, this type of genetic testing compares segments of DNA termed restriction fragment length polymorphisms (RFLPs). By using special restriction enzymes, the DNA molecule is cut at base sequences, also known as recognition sequences or restriction sites.

There are many different kinds of restriction enzymes. Each type will only cut the DNA when it encounters a specific combination of bases; A, G, T, and C. Different restriction enzymes cut DNA at different places—each has a unique sequence it recognizes. For example, the restriction enzyme named EcoRI cuts DNA when it encounters the sequence GAATTC and will cut only at that sequence, no other.

Gel Electrophoresis

After being cut up, the restriction fragments of each genome (mother, father and baby’s) are separated, according to length, using a technique called gel electrophoresis. Since people who are closely related have similar DNA, the DNA of more closely related individuals will show more similar length fragments of DNA.

Gel electrophoresis enables the lab technician to see which DNA fragments of the mother are shared by the child and, more importantly, if some of the child’s DNA fragments are the same size as fragments found in the supposed father’s DNA sample.…

X-Inactivation in Chromosomes: Mosaicism in Females Lessens Instance of X-Linked Diseases

Chromosomes encapsulate DNA and are responsible for every physical aspect and a host of personality traits of every human body. Humans have 23 pairs of chromosomes. Men and women have all the same types of chromosomes, except one vital pair. In women the last pair will be XX. In men the last pair will be XY. Whether or not the last chromosome pair is XX or XY is determined by the male sperm.

Human Genome Project

The quest for the map of human chromosomes was started in 1990. Surprisingly, the project was fully completed in May 2006. The results have already poured mounds of new information about genetics into the biology world.

For instance, one thing determined was that the X chromosome has many more genes than the Y chromosome. Due to less genetic material from their fathers, males are 6% more genetically similar to their mothers. Male twins are also slightly more identical than female twins due to less genetic information, according to Natalie Angiers, in her book Woman: An Intimate Geography.

X and Y Chromosomes

According to the U.S. National Library of Medicine, it was determined that the Y chromosome contains about 70+ genes. The X chromosome carries about 2,500 genes, and is responsible for about 300 specific diseases, including colorblindness, prostate cancer, hemophilia, baldness, Duchenne muscular dystrophy and many mental retardations, as reported by Jai Dennison at Daily News Central, in his article, “X-Chromosome Studies Unlock Deep Mysteries About Gender Differences.” Women are less likely to suffer from these X-linked genetic diseases due to what is called X-inactivation.

X-inactivation and Mosaicism

When two X chromosomes come together to create a female embryo, X inactivation occurs. During X-inactivation, cells randomly chooses to “shut down” sections of its extra X chromosome to form a “mosaic” of genes.

Consequently, X-linked diseases are more common in men than women, since women have both Mom’s and Dad’s X genes to pull from. Scientists are still discerning just how “random” the X-inactivation process is. Philip Avner and Edith Heard’s article “X-Chromosome Inactivation: Counting, Choice and Initiation” discusses interesting research in this area. Similar to the reason that tortoise-shell cats can only be female, X-inactivation creates a mosaic of X-linked traits in women but not in men, who are subject their single X’s full expression.

Inheritance and the X Chromosome

Because men only have one X chromosome, men may inherit their mother’s genetic diseases related to the X chromosome but will never inherit their father’s X-linked genetic diseases, since men only receive their father’s Y chromosome. While men escape any X-linked diseases from their father, they are vulnerable to and likely to fully develop any of the X-linked diseases given to them on their mother’s X chromosome.

In contrast, women’s double X requires that both parents have a gene an X-linked disease and even then severity of inherited disease will likely vary due to the fact that during female development random sections of the X-chromosome are inactivated. A woman is less likely to develop X-linked diseases, and more likely to develop a light instance if a disease should develop.

In conclusion, nature appears to have a “back up plan” for women through X-inactivation, while unlucky men must suffer the full severity of X-linked diseases.…