Human evolution - biological and cultural
For about 6-7 million years ago excreted from the same pre-mother chimpanzees and a number of other species, several of which utilized hind legs for locomotion more than the chimpanzees do. 3 million years ago, the African savannas reached a design that is not very different from today's. Around that time emerged Homo erectus, a fully upright walking species with an entire tool box, signs of some kind of culture, and knowledge to utilize the fire. Erectus is the first human species to leave Africa. Their tools and simple artifacts have been found in many places between Eastern Europe and Western Asia.
Later emerged even more complex cultures borne by beings who also were anatomically very similar to us. When Homo sapiens as a species was born sometime around 150 000 years ago, we were not the only human species, there were more. Today we are the only hominid left, and the reason is disputed among scholars. The dominant view today is that our survival depended on our ability to communicate and collaborate.
Today most scientists believe H sapiens descended from Africa, although there are opponents. And the exodus has gone in waves for a very long time, perhaps 100 000 years. More human species than homo erectus, and sapiens may have emigrated. What did they bring with them when they started walking? The fire, utilities, defense weapons. Drums? Most peoples use drums of some kind. Did this tradition emerge in Africa and then was brought with the migrators? Or did it arise independently in many places and independent of other cultures? We believe in the former, because in Africa there are drums everywhere.
We also believe that the original African cultures laid the foundations for a social model that was also accompanied on walks across unknown lands. If the San people in Botswana, Hadzape in Tanzania, and the Batwa in Central Africa, are the most original peoples (which the researchers believe), then their gender equality model should also have been "exported" out of Africa and spread over the earth. An effective model of society where physical weakness per individual compared with wild threats was compensated with superior communications skills where every individual's contribution will benefit the group's well-being.
Biological and cultural evolution has many consistent traits. Long after the exodus from Africa occurred a to humanity vital cultural evolution, but this text is about biological evolution.
Biological evolution - broadlyAs a scientific theory evolution is still partly controversial. What Darwins deed actually meant, how his theory in some parts have been modified, and what evolution really means, there are muddy public perceptions. Many have understood species change over time, but often speaks of "adaptation". How is it, what processes are hidden under such a sweeping statement?
The other half of the explanation is the rapid variant. More on that in the next section.
Evolution is, in short, organic life in response to changing environmental conditions. It has no meaning and no goal. It manufactures "prototypes" on purely random basis. Continuously and constantly. Those that fit well or at least is not disadvantagous in the prevailing environment survive, the others disappear.
What does it mean to create "prototypes"?
All reproduction is the result of copying. A single-celled organism makes a copy of itself, splits, and so were they two. Others require two parties where the offspring will be approximately 50% of both. The question is: are the copies exact copies? If that were the case, today living unicellular species that evolved billions of years ago should look exactly the same as then. Resistant bacteria would not exist, how would they have occurred if an organism can not change?
The change, i.e. evolution, is possible because copying in these contexts never delivers a 100% copy of the original. In the long DNA spirals with hundreds of millions of connections, errors occur. Most are minor and could in the long term lead to a slight change in one species, such as changes in skin or fur/hair. It is these variations that are active during periods of equilibrium. A species that evolves, live and die during such a period does not change very much during its lifetime.
The great leaps become reality because of the larger mutations. Mutations are larger erratics when copying, where the result can be a creature with at least one new feature that differs to a greater extent from the rest of the population. A random "fault" which means that, for example, the thumb is moved to a position so that the hand will receive a new feature to play with. A different thumb grip could under the prevailing conditions have been a clear advantage for any primate. Other mutations may mean a clear disadvantage and will not spread through the population.
How does a new species appear?Basically in two ways that we have already mentioned: Slowly where two species are separated geographically and begins two different evolutionary paths, or quickly at major ecological changes.
The slow seems easy to understand, the fast is more exciting and complex. The theory of "punctuated equilibrium" sees evolution at turbo speed as a driving force in speciation. It boils down to peripheral groups of a species living in the borderland between areas where it is possible to survive, and where it is not. If the groups are small, 20-30 people, mutations can quickly spread. Major changes in environmental pressures require larger changes in the mutations for survival. During such periods the population survives only if the evolutionary response is sufficient.
During a few million years, in geological terms a wink, appeared for example on the savannahs of East Africa species never before seen on earth. All caused by the African Rift Valley emergence and creation of completely new habitats where every available niche waited to be filled.In this way, biological evolution is seen as a gigantic and constantly ongoing "trial and error". Pure coincidence send out new models on the market that survive, or go under.
Perhaps the easiest to understand is "simple" organisms speciation. Take viruses as an example. Viruses do not have their own metabolism, but must take over a host cell, and then control and let the cell feed it. They multiply very quickly, the mutations are numerous per unit time.
In an US experiment a strain of a particular viral species was divided in two. One part was meticulously packed and driven tens of kilometers to another lab. In both labs the viruses were subjected to temperatures twice as high as their comfort temperature, and the normal diet were replaced with a completely different. After a few days both populations had produced new species that thrived in the higher temperature and enjoyed the new food.
However, the two virus populations had reached the same function, i.e. a species which survive radically changing living conditions, with different number of mutation steps and different types of mutations.
It shows in a nutshell nature's infinite dimensions.
The Big FiveIn connection with African safaris there is sometimes talk of the Big Five. The same expression is used among the world's biologists. But they mean the five times during Earth's history when the organic life have received hard knocks. On one of these occasions over 90% of all marine organisms died out. Life on Earth was on the verge of extinction, but survived. That time.
Long periods of relative equilibrium has thus been interrupted by short intervals of major environmental changes. They spell great changes of sea level and temperature, which poses challenges for the survival of the species. Species-rich zones where water meets land turns into seabeds or shore, depending on whether the water level rises or falls.The fossils tell a story of quiet periods punctuated by periods where major extinctions have occurred, after which life bounced back but with new dominant species on the scene.
An extreme example is the latest mass extinction when most of the dinosaurs died out. Today a virtually unanimous scientific community points to the impact of a meteor that 65 million years ago hit today's Mexico as the single biggest reason for this mass extinction. This meteor measured over 10 km in diameter and the explosive impact corresponded to millions of Hiroshima bombs. The dust cloud that catapulted up into the atmosphere caused a several month long global solar eclipse. In addition, the impact very well may have triggered increased volcanic activity in a wide area around the crash site, and thus accelerated the amount of dust particles in the atmosphere.The most fertile vegetation died, hence the large herbivores, and finally the large predators. Smaller animals, like contemporary mammals lived in less popular niches, were more omnivorous and survived the crisis.
As conditions stabilized, the amount of vacant niches to occupy were numerous. The mammalian era had come, by pure accident.
Average life expectancy of a species is 1-2 million years. 99.99% of all species that once evolved no longer exists.
The question is what today's climate with acidified oceans will result in.