berger@aecom.UUCP (Mitchell Berger) (05/07/85)
*** REPLACE THIS LINE WITH YOUR MESSAGE ***
This is an innocent question, not intended to be an attack.
So give me an answer, not a defence.
I was just wonderin'... If evolution happened in abrupt
changes, wouldn't two animals have to undergo the same
(or a similar) change? I mean, if in each step the new
species can't breed with the old, we would need two of
the new species in order to get something started.
What's the chance that there are two animals, 1 male and
female, within the general vicinity (close enough so that
they could find eachother), undergo the same drastic change
in the same generation?
--
Micha Berger
2525 Amsterdam Ave. Suite M406 NY, NY 10033 (212) 781-0756
{philabs|cucard|pegasus|rocky2}!aecom!bergerhua@cmu-cs-edu1.ARPA (Ernest Hua) (05/09/85)
___________________________________________________________________________ > From: berger@aecom.UUCP > > This is an innocent question, not intended to be an attack. > So give me an answer, not a defence. > > I was just wonderin'... If evolution happened in abrupt > changes, wouldn't two animals have to undergo the same > (or a similar) change? I mean, if in each step the new > species can't breed with the old, we would need two of > the new species in order to get something started. > What's the chance that there are two animals, 1 male and > female, within the general vicinity (close enough so that > they could find eachother), undergo the same drastic change > in the same generation? Good question. I assume that you are refering to punctuated biological evolution. This idea does not call for speciation at an instant. It merely says that gradual changes do occur, but in rapid succession such that the intermediates between stable forms are few. The changes still must be gradual so that breeding and proliferation may occur. The only real difference between gradualism and punctualism (I wonder if this is a valid name for it; anyone know?) is that the changes occur in narrow groups rather than in uniform spacing (on a time line). Thus, the forms that occur in great numbers in the fossils are likely to be stable forms, and the forms that occur in relatively few numbers are likely to be unstable "transitional" forms. (That is quoted because every form can be considered a transitional form. The usage here refers to forms that are intermediates between stable forms.) ___________________________________________________________________________ Live long and prosper, but don't evolve; you might get some people very angry! Keebler { hua@cmu-cs-gandalf.arpa }
rlh@cvl.UUCP (Ralph L. Hartley) (05/09/85)
> This is an innocent question, not intended to be an attack. > So give me an answer, not a defence. OK > I was just wonderin'... If evolution happened in abrupt changes, > wouldn't two animals have to undergo the same (or a similar) change? When people say "abrupt" they don't usually mean THAT abrupt. Any process that takes less than 10,000 years appears instantainious in the fosil record. No one is talking about new species apearing in one generation. (Some people have proposed mechanisms that could operate in as few as hundereds of generations however.) Ralph Hartley rlh@cvl
mrh@cybvax0.UUCP (Mike Huybensz) (05/09/85)
In article <1534@aecom.UUCP> berger@aecom.UUCP (Mitchell Berger) writes: > I was just wonderin'... If evolution happened in abrupt > changes, wouldn't two animals have to undergo the same > (or a similar) change? I mean, if in each step the new > species can't breed with the old, we would need two of > the new species in order to get something started. > What's the chance that there are two animals, 1 male and > female, within the general vicinity (close enough so that > they could find eachother), undergo the same drastic change > in the same generation? This requirement would only be true in certain special cases. If the change formed a sexual reproductive barrier and if the organism was incapable of producing offspring without a different sexual partner. That's why there is an emphasis on gradualism in evolution. (Even punctuated equilibrium doesn't require the excessively hasty change you suggest.) However, there are organisms where that sort of change can occur. One example is autopolyploidy in plants. If the plant produces both pollen and ovules, it can produce sexual offspring with itself. Or, (in automixis) the plant can produce seeds from somatic cells until it encounters another that it can interbreed with (a common occurence in dandelions and rice.) Or, it can propagate vegetatively without seeds until a partner shows up. In the animal kingdom, there are also numerous possibilities. Parthenogenesis can make do until a partner appears (as in whiptail lizards and numerous fish). Some mites with haploid males can produce a male offspring, mate with it, and then raise daughters. -- Mike Huybensz ...decvax!genrad!mit-eddie!cybvax0!mrh
ward@hao.UUCP (Mike Ward) (05/10/85)
> I was just wonderin'... If evolution happened in abrupt > changes, wouldn't two animals have to undergo the same > (or a similar) change? I mean, if in each step the new > species can't breed with the old, we would need two of > the new species in order to get something started. I think you misunderstand the meaning of the term 'abrupt' in this context. I know of no scientist who thinks that new species evolved in a single generation. The abruptness that seems part of Punctuated Equilibrium is only abrupt when viewed from the perspective of geological time. There is every indication that such changes take *at least* many thousands of years. When charted on a four billion year scale, they look abrupt.
keithd@cadovax.UUCP (Keith Doyle) (05/11/85)
[......................] >I was just wonderin'... If evolution happened in abrupt >changes, wouldn't two animals have to undergo the same >(or a similar) change? I mean, if in each step the new >species can't breed with the old, we would need two of >the new species in order to get something started. >What's the chance that there are two animals, 1 male and >female, within the general vicinity (close enough so that >they could find eachother), undergo the same drastic change >in the same generation? >-- >Micha Berger Note that 'abrupt' is used as a relative term. I'll try to use an example. Let's say there is a large population of some animal, and they live in two valleys. One day, some environmental change occurs that has two effects, a) it seperates the two valleys from each other, thereby dividing the population into two groups, and b) effects the characteristics of only ONE valley such that the environment is drastically changed. At this point, the animals in the unchanged valley probably tend to continue on as before. However, the animals in the changed valley may not be used to their new environment. Some animals will have characteristics that improve their chances for survival in this new environment, while others will die out. Over time, these new characteristics will be passed to offspring, eventually producing a entire population that is better adapted to the new environment than the population in the other valley. In addition, it is possible that the animals that had these more useful characteristics also had other characteristics in common. These traits too, may tend to become distributed throughout the population. If by some chance one of these traits affects sexual attraction, then even if the two populations are combined again for some reason, they still may tend not to inter-breed. Over long periods of time, enough such changes can occur as to make the two populations so different, that they may no longer be able to interbreed, and/or are effectively differing species. Changes in environment, therefore could be a major mechanism, and, drastic environmental changes may force a portion of a population to adapt quickly or die out. When the environment is relatively stable for long periods of time, populations may tend to stabilize, or only adapt to their stable environment with minor improvements. I hope this helps. It is a misinterpretation to think that Punctuated Equilibrium is saying that changes happen overnight. P.E. postulates quick adaptations (relatively) followed by longer periods of statis. 'Quick' in terms of evolution is still thousands of years. Keith Doyle # {ucbvax,ihnp4,decvax}!trwrb!cadovax!keithd
ethan@utastro.UUCP (Ethan Vishniac) (05/13/85)
> I was just wonderin'... If evolution happened in abrupt > changes, wouldn't two animals have to undergo the same > (or a similar) change? I mean, if in each step the new > species can't breed with the old, we would need two of > the new species in order to get something started. > What's the chance that there are two animals, 1 male and > female, within the general vicinity (close enough so that > they could find eachother), undergo the same drastic change > in the same generation? This is an irrelevant question. Punctuated equilibrium "jumps" involve a few thousand (or even hundred years) not a single generation. A mutation that drastically changed an animal in a single generation would involve a single gene. Either the new animal would still be able to breed with the rest of the population (most of the barrier to crossbreeding is biochemical and would be unlikely to be correlated with a particular structural change) or it wouldn't. If it wouldn't then the mutation would as you say, have to be a common one to provide the basis for a new species. "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas