The probability of a human body

[Pebbilita]

Hi Guys, i don't really want to get into any creation Vs evolution debates but I was just wondering if there had been anyone who had tried to calculate the probability of all the components of the human body evolving at the same time. ( or within a timeframe where they were of usefullness to each other) e.g. heart/circulatory system/ nervous system/digestive system..... hope this qustion makes sense,......
thank you!

[woofgang]

That actually is one of the creation vs evolution arguments and assumes that the useful component is the fully evolved one which is a flawed assumption. Any system for deriving nourishment from intaking and changing external matter is beneficial compared to an organism that can only absorb predigested matter. Any system for perceiving the world via touch sight etc is beneficial compared to an organism that is totally sensorily isolated from its environment.

[jomifl]

I don't know whether it is a question of probability, more a question of inevitability. Consider how many times eyes have been evolved in different genera of animals, some of them appearing to be very similar though having got there by a different evolutionary path. It seems that if a feature confers a survival advantage then it will evolve if physically possible. Wings have evolved in fish, birds, mammals and insects. When one feature evolves slightly other features evolve if necessary to support it.

[woofgang]

or rather jomifli. where one feature evolves without the others to support it, the organism doesn't survive. Where a feature evolves that confers a survival advantage then the organisms that have it will supplant the ones that don't in their particular ecological niche.

[sandyRoe]

Didn't the appendix develop and then become obsolete?

[woofgang]

in people, rabbits still use theirs

[jomifl]

agreed woofgang, I should have made that clearer but didn't think I could do better than Darwin.

[igtretd]

Richard Dawkins: Climbing Mount Improbable is worth a read on this subject.

As to your original question Pebbilita, it's an impossible calculation. How do you define a component? A cell, a group of cells? Which group of cells?
Starting from what point? A collection of simple molecules, a complex molecule, which complex molecule? Having defined a start point you would then have to calculate the probabilities of likley outcomes for a range of mutations and environments (temperature, pH etc).

One of the problems I think we have in trying to comprehend how complex organsims have evolved is we tend to think in terms of the probability of things happening based on our own experiences. These experiences typically involve fairly simple systems over very short time periods, tens of years, whereas the evolutionary laboratory is vast and complex and has been operating for thousands of millions of years.

[jomifl]

yet Igtretd.... quite

[woofgang]

jomifl, I just get uncomfortable with statements like "evolves to support" even if Darwin did say it because it can be interpreted as a kind of decision or planning on the part of evolution...what actually happens is that if one successful mutation needs something else to make the success work then all the individuals who only have the one mutation will fail but the ones that have both will succeed. Eg something evolves the ability to digest external matter but no way to get it inside the organism or vice versa...the mutations that succeed will be the ones that can both ingest and digest no matter how infrequently or weakly.

[Andyvon]

I think you'll find Sandy and Woofgang that the human appendix isn't 'obsolete'. In recent years it's been realised our appendix forms a store of the essential bacteria our gut needs to process food. During a gastrointestinal disease, our body evacuates all bacteria from the gut, good and bad. The appendix contains a store of the essential bacteria we need from which our intestines can be re-populated.

The human appendix isn't called upon so much in our cleaner, Western society. However, it was important to our ancestors, as well as to people in less developed areas of the world today when they contract intestinal disease. If someone has had their appendix removed, they must be given essential bacteria to repopulate their intestines as they can't do it naturally.

As with the spleen until recently, it used to be said you "Don't need your appendix and can survive without it". Well, the same goes for your left leg - or both legs for that matter! Nature has provided the appendix for a very good reason and it still has a function.

[jomifl]

woofgang I take your point and I was being a bit lazy with my wording but I was trying to avoid being too wordy. Perhaps I should have said 'subsequent mutations which confer an additional advantage by improving the effectiveness of existing mutations' or some such. I was speaking in general terms but you are quite right all mutations really stand on there own although there must be occasions when a mutation which confers no significant advantage on its own does confer an advantage in the presence of a subsequent mutation. Admittedly this is less likely to happen than a straight forward one mutation advantage.

[wildwood]

Yes, the timeframe is 3.5 billion years.

[woofgang]

Thanks for that Andyvon, I didn't know that!

[mibn2cweus]

In hindsight, the probability of anything happening that has happened is 100%. The future is as certain as the past but only an understanding of causality, the rules governing change, can provide us with clues as to what that future will be. With any luck, reason will prevail or perhaps one should say, reason is inevitable and with any luck, humanity will comply and conform to that inevitability. However unlikely our continued survival may be, the probability rests on our willingness and success with continuing down our evolutionary trail and adapting to the subsequent inevitable challenges that await us. However improbable and remarkable, we've made it this far . . .

[jake-the-peg]

//the human appendix isn't 'obsolete'. In recent years it's been realised our appendix forms a store of the essential bacteria//

Can't be that essential when so many people are walking around having had theirs removed will no ill effects!

Pebbilita I would suggest that the probability of all the components evolving at times that they would be of use to each other is

a) unknowable because you have to know the conditions at the pecise times that these things occurred

b) actually very likely (ie not improbable at all) because in most cases the features serve several purposes and so stick around for quite a long time before a mutation or change in environment gives them a secondary use.


For example feathers are usefull as insulation whether or not they are usable for flight. They are also useful for breeding displays regardless of usability for flight - see peacocks

[jake-the-peg]

Oh you might Payday Loans to check out the Drake equation

http://en.wikipedia.org/wiki/Drake_equation

This was an attempt to work out the probability of extra-terrestrial life. But if you take part of it out you might get what you want.

The original work estimated the probability of life occuring on a suitable planet to be 100% and the probability of that life evolving into intelligent life at 100:1

[igtretd]

@jake-the-peg

The Drake equation contains an explicit probability of 'intelligent life' evolving. The problem however is that we only have one data point, the earth, which makes an estimate of the probability of life elsewhere entirely speculative.

I suggest the original estimates of 1% for each of the factors were more a 'try for fit' rather than being based on any empirical data or bottoms up calculation of the probability of life evolving that was the subject of Pebbilta's original question (and is in any case meaningless).

For the opposite side of the coin see the 'Fermi paradox' from the same source at http://en.wikipedia.org/wiki/Fermi_paradox

Back to my previous comment on the scale of things, there are trillions of stars in the universe at distances we cannot comprehend but, because of the limitations of the speed of light and our technology, we can only observe detailed planetary conditions withiin our solar system, so whilst the chances of us finding intelligent life are small because of this restricted view, the number of intelligent civilisations may be large because of the vastness of the cosmos.

Which shouldn't stop us looking for extraterrestrial life, just best if we don't expend too much time, money and effort given the problems closer to home.

[mibn2cweus]

Given what we now know, it seems fair to suggest that as far as planets suitable for the development of intelligent life goes, at this point we've been presented with the Earth a one in a million opportunity to succeed. At any rate it would be a shame if we blow it.

[Answerprancer]

Why do people pre-empt questions with obvious outcomes with the obvious outcome ?

(eg. "It's not that I dont trust you but, would you mind awfully if I drove as you are clearly stotting drunk".)

As a supporter of the theory of evolution, I believe that different elements and combinations of cellular construction could have evolved at different rates, mostly due to outside influences/conditions and environments.

( btw. It's not that I was suggesting that you are drunk or incompetant in any way :-) )

[mike11111]

I suppose there are lots of bits we can lose and still get by. Still, I think everything must be there for a reason. 40 years ago I had my spleen removed as the result of a car accident. Was told that I could live quite happily without it. Wasn't told about the the role it plays in sustaining the body's immune system, which is why I now have to take a small dose of antibiotics every day.