Source:WhyEvolution is true
Author: Matthew Cobb
1.Evolutionary biology is ruled by handful of logical principles, each of which has repeatedly withstood rigorous empirical and observational testing.2. The rules of evolutionary biology apply to all levels of resolution, be it DNA or morphology.3. New methods merely allow more rapid collection or better analysis of data; they do not affect the evolutionary principles.4. The only mandatory attribute of the evolutionary processes is a change in allele frequencies.5. All novelty in evolution starts as a single mutation arising in a single individual at a single time point.6. Mutations create equivalence more often than improvement, and functionlessness more often than functionality.
7. The fate of mutations that do not affect fitness is determined by random genetic drift; that of mutations that do affect fitness by the combination of selection and random genetic drift.8. Evolution occurs at the population level; individuals do not evolve. An individual can only make an evolutionary contribution by producing offspring or dying childless.9. The efficacy of selection depends on the effective population size, an historical construct that is different from the census population size, which is a snapshot of the present.10. Evolution cannot create something out of nothing; there is no true novelty in evolution.11. Evolution does not give rise to “intelligently designed” perfection. From an engineering point of view, most products of evolution work in a manner that is suboptimal.12. Homo sapiens does not occupy a privileged position in the grand evolutionary scheme.I think the main thing that’s not quite right about this is 5, “All novelty in evolution starts as a single mutation arising in a single individual at a single time point”. While this is essentially true, it misses out two of the most significant novelties in the history of life, which were not created by mutation, but instead by instances of predation that went wrong and instead produced symbiosis, with one kind of cell living inside another.
The first such event took place around 2 billion years ago, somewhere in the ocean. Prior to that moment, all life had consisted of small organisms called prokaryotes which had no cell nucleus or mitochondria (these are the tiny cellular structures that help provide you and me and giraffes and mushrooms with energy). Everything changed when one unicellular life-form, known as an achaebacterium, tried to eat another, called a eubacterium. On this one occasion the eubacterium survived inside its would-be predator and became trapped, losing many of its genes to its host and eventually turning into a molecular powerhouse – the mitochondrion – that produced energy from chemical reactions and was used by the new eukaryotic cell. These new eukaryotic life-forms were a weird hybrid, composed of two different organisms. They were our ancestors.
A second, similar, event occurred around a billion years ago, when a eukaryotic cell, complete with mitochondria, engulfed a eubacterium that had long ago evolved the trick of acquiring energy from sunlight, through photosynthesis. Predation went wrong again, and another form of symbiosis eventually appeared. This gave rise to algae and eventually plants, in which small organelles called chloroplasts, the descendants of the intended eubacterial victim, turn light into energy for the benefit of the eukaryotic host.
What happened after these events took place was entirely down to natural selection, following the kind of processes that Dan describes above. But the source of the novelty – and pace his point 10 above, these were truly novel organisms – was not mutation, but an incredibly unlikely pair of events.
It is striking that these two acts of predation gone wrong were able to open up the potential of life in ways that genetic mutation + natural selection have not been able to do in 3.5 billion years of evolution. Life on Earth without mitochondria – prokaryotic life – is limited to the microscopic because of the physical limits imposed on the transport of matter, energy and information from the environment into the inside of the organism. In the absence of an additional, powerful energy source, prokaryotic life cannot carry out those operations beyond certain tiny physical dimensions. The co-option of the energy-producing mitochondria first enabled eukaryotic cells to grow large, and then, eventually, to become multicellular. Mutation and natural selection were not able to do this. Similarly, no eukaryotic organism has on its own mastered the trick of evolving photosynthesis; the only way the ancestors of plants were able to do this was through symbiosis with photosynthetic bacteria.