…my distant relative is a lower life form

[The Leaven – exploring the relationship between science and religion (cont)]

Through research by evolutionary biologists we have now discovered that humans are more closely related to leaven than early civilisations could have imagined. Many of the human proteins involved in the fundamental functions of the cell,such as DNA replication, are conserved in other organisms, even in yeast and bacteria. In fact some human DNA can be expressed in bacteria and yeast to produce protein. Proteins that are homologous in different species are known as orthologues. DNA processing proteins, such as Polymerases, are often found in this category. For this reason the mechanisms of mutation in mammalian cells can be studied equally as well in yeast cells.

The big question is then why did not all yeast cells evolve into complex multicellular organisms like humans or even plants? Why are there still primitive cells like bacteria? As George Carlin, so eloquently put it:

If man evolved from monkeys and apes, why do we still have monkeys and apes?

The answer is that organisms are continually evolving, they are constantly finding new ways to preserve or obtain energy, therefore new species could arise at any time and, as a consequence, there must always be lower and higher life forms. It is the diversity of Life that encourages adaptations. Through a constant competition to obtain energy, diversity provides the resources on which selection can act. For instance, a group of higher species A are infected by lower species B and some are killed. Some A species were able to survive because they have a mutation that makes them more resistant to species B  but it also makes them less resistant to species C. It flourishes until it encounters species C. As consequence of  this cycle of adaptations, species A no longer resembles its original form and becomes subspecies Ab. So evolution depends heavily on a changing environment and the ability of an organism to adapt.  This allows the evolutionary route to continue in a perpetual cycle of various adaptations until many species of organisms evolve. Darwin called this process natural selection or the preservation of favoured races in the struggle for life:

If under changing conditions of life organic beings present individual differences in almost every part of their structure, and this cannot be disputed; if there be, owing to their geometrical rate of increase, a severe struggle for life at some age, season, or year, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of life, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, it would be a most extraordinary fact if no variations had ever occurred useful to each being’s own welfare, in the same manner as so many variations have occurred useful to man. But if variations useful to any organic being ever do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance, these will tend to produce offspring similarly characterised. This principle of preservation, or the survival of the fittest, I have called Natural Selection. It leads to the improvement of each creature in relation to its organic or inorganic conditions of life; and consequently, in most cases, to what must be regarded as an advance in organisation. Nevertheless, low and simple forms will endure if well fitted for their simple conditions of life.

[Darwin, 1859]

Evolutionary selection relies on the chance that an adaptation will occur and that it will improve the fitness of a particular organism. This directly conflicts with early Christian beliefs that organisms do not evolve and remain as they were originally conceived.

Gradual evolution of 21st cent humans. A schematic representation by José-manuel Benitos.

The discovery of humans at various stages of evolution has diminished the concept that humans were created in their current form or generated spontaneously. Humans are thought to have evolved from primates that first appeared around 5-8 mya and share many similar characteristics to chimpanzees. In fact 98% of chimpanzee DNA is homologous to human but one of the greatest anatomical differences is in brain size. The chimpanzee’s brain weighs less than half a kilo while a human brain weighs around three times that much. Archaeological evidence suggests that three or four hominid species lived in the African continent several million years ago. Currently one of the earliest of these is known as a species called Ardipithecus ramidus.  Modern humans, Homo sapiens are thought to descend from Australopithecus anamensis, Australopithecus afarensis, Homo habilis and Homo erectus. There are other early hominids that are thought to be more distantly related Australopithecus africanu, Paranthropus aethiopicus, Paranthropus boisei and Paranthropus robustus.  The hominid that began to be dispersed around the globe was the bipedal Homo erectus. This species is thought to have evolved into Homo sapiens only 200,000 years ago, a blink of an eye in evolutionary terms.


2 thoughts on “…my distant relative is a lower life form

    • Thank you.. an idea for another post.. sporulation and meiosis in yeast. From what I recall, although the processes of sex is extremely energy consuming, and a bit risky, it leads to greater diversity and therefore a better chance of adaptation. Actually, after reading the post again, I think I should have used environmental factors rather than other species as the factors for adaptation.. otherwise where did species C come from?

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