87
edits
Changes
Jump to navigation
Jump to search
Line 1:
Line 1: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Talk:Question evolution! campaign (view source)
Revision as of 00:27, September 14, 2011
, 00:27, September 14, 2011no edit summary
[[Talk Question evolution1 campaign archive 1|archive 1]]
[[Talk Question evolution1 campaign archive 1|archive 1]]
==A Biologist's Answers to the "15 Questions"==
1. '''How did life originate?'''
:Truthfully, we don't know. Science is built upon repeatable evidence as provided by observation and experimentation. There is very little evidence, one way or the other, regarding the exact mechanism of the origin of life. Science cannot rely on dogma, and the existence of scripture is hardly evidence in support of divine creation; therefore the most scientifically sound answer here, relying on the evidence, is that we do not conclusively know. That said, there are a few good hypotheses that have been presented--notably the "RNA world hypothesis", for which there is actually quite a bit of evidence--but not a single one of them can be conclusively demonstrated yet.
:Organic compounds, such as amino acids and nucleic acids, will form spontaneously--albeit in trace amounts--wherever the proper elemental ingredients (Carbon, Nitrogen, Oxygen, Phosphorous, and Sulfur) and environmental conditions can be found. The common thread underlying all naturalistic hypotheses on the origin of life is that at some point these compound polymerized (which will happen spontaneously if the conditions are right) into larger polymeric biomolecules and that a very tiny minority of these molecules were able to self-reproduce. The rest, as they say, is history.
:This may seem a far-fetched phenomenon to happen by chance until you consider the scale on which these events happen. Out of millions of trillions of randomly formed polynucleotides or polypeptides (the actual number probably many orders of magnitude larger than that), all it takes is one with the capacity for self-reproduction to get the process started. Self-reproducing strands of RNA, for instance, can be created and identified in a lab by a much smaller-scale screening of random nucleotide sequences--that this could be the mechanism for the origin of life on Earth is quite plausible.
2. '''How did the DNA code originate?'''
:The phrase "DNA code" here is alarmingly vague. Does it reference the specific pattern of which codon encodes a particular amino acid in a protein? Does it reference interactions between nucleic acids and ribozymes (enzymatic RNA molecules)? Or does it reference the "central dogma" whereby DNA encodes biomolecules, the expression of which is regulated by cell metabolism?
:In reference to the system of 64 codons (nucleotide triplets) encoding the order in which one of twenty amino acids are incorporated into a polypeptide (a protein), we are still entirely sure. Interactions between ribozymes and amino acids form the basis of protein production in modern cells. We have pretty good biochemical insight into the function of this system but, until we get more evidence, much of its origin remains subject to conjecture.
:As for mechanisms by which DNA/RNA/Protein interactions emerged, much of it has to do with the 3-D structure of these molecules. Again, as for de-novo emergence of this system, the jury is still out, but mechanisms of variation within these systems between lineages are quite well known. In fact, comparing these variations across lineages is one of the most effective ways of understanding their functioning.
:Considering other facets of structural genetics, we actually have a pretty idea where they came from. For instance, the itron-exon / RNA splicing mechanism that allows a single eukaryotic gene to encode multiple protein-coding mRNA products seems to have emerged from bacterial retroelements. There is quite a bit of data supporting this.
3. '''How could mutations create a new biochemical pathway?'''
:They do every day. That's why old antibiotics don't work, that's why first-generation HIV drugs are obsolete, that's why my Aunt's pet poodle doesn't look like a wolf. In terms of more complex processes (say genes and proteins that regulate development) the concept is pretty straightforward. A gene is duplicated (this happens quite a bit), at first, the duplicate copy of the gene is redundant (or, depending on how completely duplicated it was, non-functional). Then, as mutations occur in the duplicate gene, it's sequence diverges and it can ultimately acquire a new function. This process is very well observed both in nature and in the laboratory.
4. '''Why is natural selection taught as evolution?'''
:It isn't. Natural selection is taught as one of the major mechanisms underlying evolution. Evolution refers to phenotypic (metabolic and morphological) change within a population of a given species over time. Other important factors contributing to evolution and speciation are spontaneous allelic variation (genetic mutation) between individuals, genetic drift (change in prevalence of a given allelic variation within a population over generations), and reproductive isolation of a given population.
:Environments change over time, an allelic variation producing a phenotypic variation that allows an organism to reproduce more efficiently in its environment will be increasingly represented in future populations. Therefore, the population will "adapt" to meet the demands of its environment over time. Natural selection is simply the tendency of individuals better adapted to their environment to reproduce more efficiently.
5. '''How did biochemical pathways originate?'''
:In bits and pieces. Many metabolic reactions are spontaneous, most enzymes simply catalyze them (speed them up). Duplicating one enzyme, and giving it time to change in structure, leads to the emergence of new enzymes. If the new enzyme confers a reproductive advantage (e.g. by allowing the cell to use a new source of fuel) then, obviously, it will become increasingly prevalent in future generations. Furthermore, by re-purposing duplicated parts from various pathways, new pathways and complex structures can, and do, emerge quite efficiently. The only caveat here is that the intermediate forms of such pathways and structures must also function to confer some reproductive advantage--again, this is also observed to be the case.
6. '''Living things look like they were designed, how do we know that they were not designed?'''
:Have you ever choked on a large bite of food, unable to breathe because we both eat and breathe through the oropharynx? Have you ever heard of the "blind spot" in the visual field of each eye? Modern organisms are overflowing with counter-intuitive "design flaws" that are leftover from the evolutionary process. While this, in and of itself, is not evidence against design, it does call into question the engineering credentials of any hypothetical designer. Furthermore, there is no direct scientific evidence to support such design. Science is all about empirical evidence, circumstantial evidence is not sound science.
7. '''How did multicellular life originate?'''
:Cells talk to one another--a lot. Even individual bacterial cells secrete and detect chemical signals, they even secrete bio-films to live communally and cooperate with one another. That individual variation would create mechanisms allowing for cells in cooperation to "specialize" and, thus, become cooperatively more efficient is not a stretch of the imagination at all. The alleles present in these cooperating cells (which are very likely to be closely genetically related) will be passed more efficiently to future generations. Multicellular life has arisen separately several times. There's quite a bit of evidence to support that this is essentially what happened each time it did.
8. '''How did sex originate?'''
:Increasing the genetic diversity of a population facilitates adaptation and is generally good for the population as a whole. Sex, in the most reductive sense, is simply the process of mixing the genetic material of two indivuals--it allows reproductive advantages conferred on an individual by allelic variation to combine with other advantageous alleles. It also protects against the effects of deleterious alleles on an individual's ability to propagate their genes. In a sense, it's a way of "hedging the bet".
:As for the origin of sex, it's been around for a long time. Even the simplest bacteria exchange genetic material with one another. As with all of evolutionary biology, an idea that works is generally kept. Why change a good thing?
9. '''Why are the "transitional fossils" missing?'''
:They're not. While the fossil record is incomplete at best, it does document, in detail, many major evolutionary transitions. For instance, we've found fossils of dinosaurs with feathers, whales with legs, and mammals (which have a distinctive hip-bone morphology) that lay eggs. Whale evolution from a dog-sized land animal ancestor is very well documented; we have intermediate fossils illustrating virtually every step of the transition.
10. '''How do "living fossils" remain unchanged over hundreds of millions of years?'''
:They don't. Even the modern organisms from the oldest lineages are different, albeit in sometimes minor ways, from their ancestral forms. The body plans and survival strategies that continue to work will continue to persist--that's natural selection!
11. '''How did blind chemistry create the mind and morality?'''
:It wasn't blind chemistry. Selection favors what is effective, what is effective then persists and can be further improved upon by more selection--evolution is not a process of ad-hoc randomness, "order" is provided by the force of natural selection weeding out less adaptive variations and favoring more adaptive variations.
:Intelligence is quite adaptive for the human ecological niche. The mind is biological, modern neuroscience is just starting to unravel the biological mechanisms underlying cognition--what we've found so far is astonishing, and it's just the tip of the iceberg! Besides that, as anybody who has ever owned a cat will tell you, many animals are remarkably intelligent; on the flip side, as anybody who has ever squished a worm on the sidewalk will tell you, many animals with more primitive central nervous systems are not.
:We still do not have the complete story behind the evolution of the human brain--but if you want to see transitional forms of cognition from more basal lineages, visit a pet shop!
:As for morality, many animals display an in-born sense of right and wrong. As a social species, an innate need to cooperate with the group and establish stable social structure is essential for human survival. While the precise biological mechanisms underlying morality are still unknown, any trait that facilitates this would be strongly selected for.
:A good case study for this is psychopathy. The underlying biological causes of psychopathy are relatively well-known, as is the phenotypic manifestation of psychopathy--put simply, psychopaths lack an inherent sense of morality.
12. '''Why is evolutionary "just so" storytelling tolerated?'''
:It isn't. Yes, as we find new fossils and new molecular evidence, we have to adjust our model of the "tree of life". This is science, we build the best hypothetical model we can with the evidence available, and where new evidence contradicts the model, we adjust it accordingly.
:Playing with his finches, Darwin never could have imagined the wealth of information and new techniques available to modern science. Yes, some of his individual predictions on relationships between species were incorrect. Indeed, many old predictions have given way to newer models as more data becomes available. However, the general idea that speciation results from natural selection acting on phenotypic variation within a population is better supported by the available evidence than it has ever been.
:Scientific paradigms and models change--that's the nature of science. Using this as the basis for refuting evolution is similar to doubting the existence of gravity because of special relativity.
13. '''Where are the scientific breakthroughs due to evolution?'''
:Everywhere! Consider recombinant insulin derived from genetically-engineered bacteria, consider much of modern epidemiology (diseases change over time), or even consider the cereal crops that humans have been ''selectively'' breeding for millenia. How about the breakthroughs that have been made in the biomedical sciences using animals to model human disease? To use disease gene research as an example, the whole justification behind studying human birth defects in mice and fish (and fruit flies!) is the relatively close (from a history-of-life perspective) evolutionary relationship between humans and these species. And this assumption of evolutionary relationships has not let us down--it gets good results!
14. '''Why is evolution taught as operational science instead of history?'''
:Ever heard of astronomy? Making observations to test hypotheses and streamline extant models is science. When a scientist in a lab does an experiment he must ''observe'' the outcome to get results and arrive at a conclusion.
:The predictions made by the theory of evolution are quite testable and are tested in labs around the world every day. In fact, evolution is an essential cornerstone in every aspect of modern biology. To go with my example from the previous question, without the paradigm of evolution much of the lab work that gets done today would not be possible.
15. '''Why is a fundamentally religious idea, a dogmatic belief system that fails to explain the evidence taught in science classes?'''
:Creationism is generally kept out of the classroom.
== One Question for Creationists ==
== One Question for Creationists ==