A Quote by Hans Adolf Krebs
The existence of common features in different forms of life indicates some relationship between the different organisms, and according to the concept of evolution, these relations stem from the circumstance that the higher organisms, in the course of millions of years, have gradually evolved from simpler ones.
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The concept of evolution postulates that living organisms have common roots, and in turn, the existence of common features is powerful support for the concept of evolution.
Evolutionary biologists often appeal to parsimony when they seek to explain why organisms "match" with respect to a given trait. For example, why do almost all the organisms that are alive today on our planet use the same genetic code? If they share a common ancestor, the code could have evolved just once and then been inherited from the most recent common ancestor that present organisms share. On the other hand, if organisms in different species share no common ancestors, the code must have evolved repeatedly.
According to the concept of transformational evolution, first clearly articulated by Lamarck, evolution consists of the gradual transformation of organisms from one condition of existence to another.
Bacteria are single-celled organisms. Bacteria are the model organisms for everything that we know in higher organisms. There are 10 times more bacterial cells in you or on you than human cells.
Number is different from quantity. This difference is basic for any sort of theorizing in behavioral science, any sort of imagining of what goes on between organisms or inside organisms as part of their processes of thought.
Perhaps genes did regulate the aging process. Perhaps different organisms had different life spans because a universal regulatory 'clock' was set to run at different speeds in different species.
The vulgarization of Darwinism that sees the "struggle for existence" as nothing but the competition for some environmental resource in short supply ignores the large body of evidence about the actual complexity of the relationship between organisms and their resources.
I am of course getting angry if biologists try to use the general concept 'chance' in order to explain phenomena which are so typical for living organisms as, for instance, those appearing in the biological evolution.
What I was concerned with was life: what are the major features that are common to all living organisms that subtly define life. So I looked at the whole problem as a chemist, as a biochemist, and as a molecular biologist.
Current organisms have a higher probability of sharing a single code if the common ancestry hypothesis is true than they'd have if the hypothesis of separate ancestry were true. That is, the simpler hypothesis has the higher likelihood in the technical sense of "likelihood" used in statistics.
If the organisms in a species now have trait T, and this trait now helps those organisms to survive and reproduce because the trait has effect E, a natural hypothesis to consider is that T evolved in the lineage leading to those current organisms because T had effect E. This hypothesis is "natural," but it often isn't true!
The issue, as correctly emphasized by Carl Sagan, is the probability of the evolution of high intelligence and an electronic civilization on an inhabited world. Once we have life (and almost surely it will be very different from life on Earth), what is the probability of its developing a lineage with high intelligence? On Earth, among millions of lineages of organisms and perhaps 50 billion speciation events, only one led to high intelligence; this makes me believe in its utter improbability.
First, Darwinian theory tells us how a certain amount of diversity in life forms can develop once we have various types of complex living organisms already in existence.
In some central and important cases, ... the existence of specific power relations in the society will produce an appearance of a particular kind. Certain features of the society that are merely local and contingent, and maintained in existence only by the continual exercise of power, will come to seem as if they were universal, necessary, invariant, or natural features of all forms of human social life, or as if they arose spontaneously and uncoercedly by free human action.
The relationship between the United States and Mexico goes over and beyond the relationship between two governments. This is a relationship that has been built as of two peoples who have a common life, or millions of people who have their everyday lives in both nations; a relationship that undoubtedly involves millions of inhabitants of both countries.
The theory of natural selection is the centerpiece of The Origin of Species and of evolutionary theory. It is this theory that accounts for the adaptations of organisms, those innumerable features that so wonderfully equip them for survival and reproduction; it is this theory that accounts for the divergence of species from common ancestors and thus for the endless diversity of life. Natural selection is a simple concept, but it is perhaps the most important idea in biology.
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