The Geological Record

Earth’s history is written in stone. The rocks you see on the ground and the rocks beneath your feet contain layer upon layer of geological narrative. These layers were there 500,000 times further than recorded human history. Like scrapbook, these layers filled with mementos in the past.

The earliest pages tell a story of a billion years ago, when our planet was a red-hot ball of liquid metal, no breathable air, and inhospitable to life. Then, 3.5 billion years ago, the arrival of oxygen, a form of gaseous waste product puffed out by photosynthetic bacteria, brought the turning point. The oxygen reacted with silicon, phosphorus, and calcium to make new chemicals, which could dissolve in water. Occasionally, chemicals that contain chemicals so concentrated that they produced a crystalline film over rocks and even living things. Acritarchs, those early organisms, became the first fossils.

Acritarch fossil
Acritarch fossil

Acritarch fossils show early steps of evolution, but they are difficult to be interpreted. Oxygen burns molecules, as a fire burns tinder. As a result, early creatures were forced to adapt or die. Survivors teamed up, one living inside another, to get used to the rise in oxygen level. Those survivors, 2-billion-year-old creatures, finally became plants, mushrooms, and even human.


Sexual Selection

Darwin introduced the idea of sexual selection as a complementary to natural selection. In the living world, one sex, usually the female, invests more in reproduction process. She has standards to choose the best males to mate with. On the other hand, males can mate with many females. In order to spread one’s own genes as many as possible, the males compete with each other based on females’ standards in order to win the chance to mate with females.

red deer
Two red deers competing with each other

The picture above shows two male red deers competing with each other. They are trying to show their strength and fitness to attract female. Some female doesn’t choose male based on the strength. For example, peacock. The male peacock that has the most beautiful and incredible tail always attracts a female peacock. Such selection has no apparent relationship with fitness, but “ornaments”. By selecting peacock with beautiful tails, a female will have “sexy sons”, who can pass on her genes in the future.

A male peacock showing his tail

So, has sexual selection influenced the evolution of human? Although there’s not so many academic research to prove it, but it will be doubtful to say no. Some scientists have suggested that our brains are the result of sexual selection. Our ancestors viewed intelligence as one of the standards while selecting partners to mate with, so that we become smarter and smarter during the evolution.

Paradox of Sex

There are lots of discussions about the maintenance of sex. Seeing many species get along perfectly well without males, why is sex still important? Unless something stops them, asexual species can grow exponentially – one, two, four, eight, sixteen …They can produce clones of themselves and some of them can have over 1 million descendants after only a few days. So, why does sexually reproducing still necessary?

Difference between sexual and asexual reproduction

The picture above shows the different between sexual and asexual reproduction. This is the main reason why sexual reproduction is important for evolution. Theoretical evolutionary research has put forward more than 25 hypotheses in the 1970s and 1980s to explain the advantages of sexual reproduction in evolution. The hypotheses can mainly be divided into two groups, both of them point out that sexual reproduction reduces the risk of extinction.

First, sex provides novel genetic variation in offspring by reshuffling genes during recombination and meiosis. Thus, it will provide opportunities for novel fast adaptations. Only sexual reproduction can reshuffle genes because the offspring will mix the feature of both parents, asexual reproduction will have offspring identical to parent. Also, sex removes negative deleterious mutations through meiosis and recombination.

Overall, although sex appears costly, it will do well to offspring for most species. Rather than asking why we need sexual reproduction, we may want to ask how those asexual species exist during the evolution.

Oedipus Complex and Electra Complex

“We cannot get away from the assumption that man’s sense of guilt springs from the Oedipus complex and was acquired at the killing of the father by the brothers banned together.” –Freud, 1930

When I talked about repression mechanism in my last post, I mentioned that Oedipus Complex is the most infamous example. The reason is that most people don’t admit they have that kind of desire described in the theory. So, what exactly is Oedipus Complex?

According to Freud, boys will experience Oedipus Complex at the age from 3 to 5. During that age period, boys wish to stay with their mothers and sometimes hate their fathers, even wish their fathers to die. The opposite is the Electra Complex. Girls are fixated on their mothers and compete with their mothers for maternal attention. This is the reason most people deny this theory because it makes them evil. However, it is actually a nature development process, everyone experiences that. As people grow older, those desires will change to someone or something else.

Stages of Freud’s Oedipus Complex



“Unexpressed emotions will never die. They are buried alive and will come forth later in uglier ways.”
― Sigmund Freud

Psychoanalysis is a set of theories related to the study of the unconscious mind. Sigmund Freud, an Austrian neurologist, established the disciplines in the early 1890s.


You must have seen some cartoons like the picture above: a character with a devilish incarnation of him or herself on the shoulder, and an angelic one on the other. According to psychoanalysis, although we can’t see those two little incarnations on our shoulder, we have them in our mind.

Central idea of psychoanalysis is that lots of human desires are beneath the level of conscious awareness. Those desires just spilling over as a neurotic tic occasionally. Also, sex plays a big role in this theory. We tend to deny some of our unacceptable desires with the repression mechanism. Freud believed a common source of psychic conflict comes from sexual fantasies in childhood. The most infamous example is the Oedipus complex, which I will explain in my next weeks’ post.

Critiques points that what psychoanalysis claims are untestable. But there are examples in today’s research showing that repression mechanism do exist.


behaviorism quote

In 1913, John B. Watson, the American psychologist, pointed out that human learning could be studied like Ivan Pavlov’s dogs. That’s the start of behaviorism.

Pavlov dog’s experiment 

Behaviorism belongs to science of psychology. It focuses on human’s measurable behaviors and see how those behaviors determine or effect their further actions. For example, by rewarding some behaviors and punishing for others, young children can learn how to behave themselves. There’s even thoughts that with appropriate condition, people can turn young children in any type of expected person.

This theory dominated the science of psychology for half a century until 1960s. People started to realize that thoughts inside our heads cannot be measured, so the behavior would be hard to predict or determine. Also, evolutionary psychology made people think about the inheritance of intelligence and personality, and could hardly be learned.

Although behaviorism is no longer a dominant force in psychology, the findings of theory are still widely applied, especially in education and therapy. When you buy your child a toy because he or she achieved a goal, you are using it.

Hybrid in Biology


  • The offspring of two plants or animals of different species or varieties. For example, Cama (camel x llama)
Picture of a cama

How it happens?

  • Anthropogenic hybridization. We human can combine two different species’ DNA together and implant the fertilized egg into a female animal’s body. For example, on May 11, 1897, the first liger was born with parental traits of male lion and a tigress, under Carl Hagenbeck’s effort.


Picture of a liger
  • Natural hybridization. Although species, especially animals, often have mechanisms to prevent themselves from interbreed with other species, it happens sometime. For example, Lonicera fly is the first known animal species from natural hybridization. Before that, natural hybridization was known to only occur in plants.
5-lornicera fly
Picture of a Lonicera fly

Hybridization can create new and stronger species, on the meantime, hybrid animals can hardly reproduce. There’s no evidence showing all of hybrid animals are suffering from diseases, on the other hand, hybrid animals always have a shorter life span. So, what do you think? Is hybrid a good thing or a bad thing?