If you can find the story “Brenda” by Larry Niven - it’s an interesting take on genetic manipulation. Doubled up superman genes for clotting leads to strokes and heart attacks by age 50; doubled up nightvision genes leads to day blindmness; stronger muscles lead to limb dislocations and broken bones; quick-reacting skin pigment leads to vitamin D deficiency; etc. Fiddling with one genetic feature is like bolting a V8 into a Volkwagen Beetle. If the engine’s too strong, the transmission will strip, and the clutch will burn; meanwhile, the engine mounts could break and the whole balance is off… You can’t change just one thing.
I think you’ll see a lot more experimentation on animals before anyone’s ready to try humans. We still don’t know that much about manipulating anything more than single-protein producing genes, and we can’t easily and reliably even clone primates. Evolution is essentially the process of throwing out a huge mess of mutations and seeing which ones (a) are better than what we used to have and (b) breed true. Who wants to volunteer their kids to see whether they come out as athletic geniuses or vegetables?
Most of recent human effort on this seems to be directed counter-evolutionary.
For example, diabetes seems to be increasing in humans. But previous to the discovery of insulin and its manufacture & prescription, most diabetics died off before they were old enough to reproduce, thus ending their family line. But now diabetics can live a near-normal lifespan, and produce children, who will carry on the genetic tendency for diabetes. The same could be said for many current medical treatments for diseases.
There used to be efforts made to sterilize patients in mental hospitals, which would tend to reduce the frequency of genetic-related mental disorders in future generations. But now, such surgery is considered ethically suspect, and not generally done any more.
No. What’s happening is that human technology is changing the environment such that genes that used to be very harmful (diabetes) are now not as harmful. Evolution is still going on, it’s just that what is ‘fit’ has changed.
It’s exactly the same as what happened millions of years ago when humans started using fire. The environment that human genes evolved in changed, such that huge jaw muscles weren’t as important for survival (and probably some others were more important, for instance a gene that finds roasted meat appetizing).
Or, when humans in Europe domesticated milk-giving cattle, it became advantageous to have a gene that kept lactose production active for one’s entire life. Evolution happens, it’s just that the ‘goal’ changes because the environment is different.
So? It was only sixty-odd years from experiments with crude gliders at Kitty Hawk to landing men on the moon, and much of that was spent developing better aircraft carriers while finding new ways for pilots to break the sound barrier. I’m fine with figuring on a lot of animal trials before we get to mankind; I’m not saying it’ll be incredibly soon, I’m just asking how far off we think it is.
There is reasonable evidence since the 1980s that it was incorrect that marsupials thrived in Australia only because there were no placentals.
Fossil records suggest that both placentals and marcupials made it to the Australian continent as or just after the split up of Gondwana. Then as time tested their adaptations in the environment, marsupials proved superior and kicked the placentals off the continent, the only place where this occurred. Having a lower metabolic rate is thought one of the key advantages. There are a few, small native placentals in Australia, though these arrived later, island hopping down the Indonesian archipelego.
Which, if you accept the notion that the global environment is under stress, would infer that the rate of evolution is increasing, not decreasing.
Just over half of all native mammal species in Australia are placentals. Not really a few.
The placentals occupied the niches that marsupials couldn’t readily occupy for various reasons: the air, the niche of small omnivores and the niche of aquatic predator. In all the niches that the marsupials could readily occupy they excluded the placentals for 50 million of years.
It was only with human gross disturbance of the ecosystem and the simultaneous introduction of mammals from every other landmass on the planet that a dozen or so placentals established in other niches. IOW under ideal conditions only about 12 placental mammals are competitive with marsupials in their home range.
And around 15% of the terrestrial mammal species in South America are also marsupials.
These points pretty much refute the commonly held belief that marsupials are somehow unable to compete with placentals.
Of course genotype and phenotype are both legitimate ways of thinking about evolution. But I was discussing how to quantify rates of evolutionary change, and it is often much easier to measure genotype than phenotype for these purposes, and especially to set up experiments to test theories about the rate of evolutionary change.
You bring up a good point, which is that you need to pick sequences of DNA which evolve at an appropriate rate in order to produce a phylogenetic tree. If you pick sequences that evolve too slowly or too quickly for the time frame you’re interested in, you won’t obtain an accurate tree. I started my post assuming that you had a reasonably accurate tree, so I left out this step.
The rate at which DNA changes and the rate of “evolution” have only a very loose relationship! DNA changes quickly: an individual has many 100’s of actual mutations, I think, compared with parents, not even counting changes due to chromosome crossover. The vast majority of these changes have no effect. “Evolution” rate measures the speed at which a population selects and amplifies the rare useful change. (The quote outlines a method where probably-useful genetic changes can be identified automatically.) That evolution rate is related to population size was my own conjecture: I hope someone will confirm or refute that. The article I alluded to mentioned geographic dispersion, which may be more important.
Unfortunately I’ve lost the URL which explained this in more detail and made the claim that human evolution was much faster during the 60,000 years since dispersion, compared with during the millions of years separating man and chimp. (This can become a racist claim, unfortunately, since the measurement is made between ethnic groups.) What I was really Googling for at the time was specific examples of recent beneficial mutations in humans. Other than skin pigment and sickle-cell, lactose tolerance is the only well-known such mutation, but I’ve stumbled on more interesting claims I’m no longer able to find with Google. :dubious:
Assuming you are using the words with their standard definition, that would be the adpatation rate, not the evolution rate.
In its broadest sense evolution is a change in allele frequencies (or more strictly a heritable change in the frequency of allele expression). So for most practical purposes the rate of evolution is the rate of change of DNA.
The rate at which a population selects for favourable change is the rate of adaptation, not evolution. To illustrate this, consider two identical populations of organisms.
Population A is subjected to only minor environmental stressors. As a result the genotype change is primarily due to genetic drift, with effectively no selection. Nonetheless after 100 generations the entire population has changed from small, green and scaly to large blue and furry.
Population B is subjected to a multitude of environmental stressors on a rotational, generational basis, however none of the stressors is novel. So a trait that confers a 90% survival advantage in one generation is worthless or even detrimental in the second and third generations, only to confer the same advantge on the fourth generation. The same applies to genes favourable to second and third generations. As a result the population remains genetically unchanged, because no single favourable mutation confers an overwhelming, multi-generational benefit. Yet the population selects for novel mutations with 90% effectiveness every single generation.
According to your defintion population A has experienced a near-zero rate of evolution because there has been nearly zero selection for favourable change, despite the fact that it has experienced radical genotypic and phenotypic changes. And conversely according to your definition population B has experienced rapid evolution because the population selects and amplifies useful traits with 90% efficacy each generation, despite the fact that after 100 generations the population remains phenotypically and genotypically unchanged.
All things being equal a larger population will evolve faster simply because it has a larger potential gene pool to draw from. However in the real world all things are never equal, and larger populations don’t actually exhibit faster mutation rates. Rather what we find is that larger populations exhibit more radically changes more rapidly through the culling of clusters.
I think far more people are aware of the genetic disease resistance of Eurasians compared with, for example, Americans and Australians, than are aware of lactose tolerance. So that’s a far better example of a beneficial, recent mutation.
I am saying that “evolution” can be used to describe change in the genome. In support of my assertion, I quote the manual for r8s, a program which does exactly what I have been describing (http://loco.biosci.arizona.edu/r8s/)
That should be clear enough, but I can find more papers on this topic if you would like.
I would suggest in a difficult environment, being a marsupial is probably a survival advantage. Considering the burden reproduction puts on the female, being able to jettison Junior at the sign of difficulty - or, bluntly, letting him starve to death without killing the mother too - is probably a survival advantage.
I was just saying that Australia’s peculiar dominant animal type - a large hopping beastie - came from a prototype or precursor that happened to favour that means of locomotion. Whether that would win against a scurying type is an interesting debate; but lacking significant opposition or entrenched competition - the hoppers filled many niches in Australia, the lemurs in Madagascar, the finches in the Galapagos…
Similarly, the ruminants seem to have dominated over the horse-type animals in other continents, since they can digest the cellulose to a gooey mess while the latter just pass it out as fluff for the road-apples. It’s all about what food is available and how well you use it, or how easily you escape being food.
How far are we from real experimentation with genes?
I ssupect we are a long way from “designer babies” just because of general revulsion. I expect some decade a regime like the North Korea, where public opinion is irrelevant, may do some serious experimentation.
The problem until then is “who”? Nobody will volunteer their kids; I suspect real genetic manipulation will sneak in the back door over about 100 years; first we will have viruses inserting genes into people to cure problems. Then we use the same trick to make the cure permanent. Then our perception of the need and value of changes will shift, much as it has with plastic surgery; we’ve gone from something that was for movie stars who needed the looks and vain but super-rich old ladies, to something girls (and guys) ask for on their 16th birthday.
Orthodonty and braces (a form of beauty enhancement) is automatic nowadays. How long before the gene for HPV resistance or straight teeth and cavity resistance or diabetes resistance or vision correction is inserted? From there, it’s only a generation to genes for blonde or height or breast size…
We have a mild tolerance for sex selection nowadays depending on motive. Wanting only boys - bad… wanting a complete set - good… So we’re on our way.
Except that placentals actually have the advantage in these situations. If you compare a sheep and a kangaroo, or a rabbit and a bettong, which are marsupials and placental sin almost identical niches, you find that the placentals can actually resorb the foetus, thus recaprturing lost nutrients, whereas the marsupials simply lose all that material.
The idea that placentals will somehow die if they abort has no basis in fact.
Except that it didn’t. The macropods are descended from generic arboreal quadrupeds. They adopted the slatatorial locomotion when they were already substantial sized beasties, in the range of 20 kgs or so. The living rat kangaroos and hare wallabies are diminutive representatives, not ancestral.
Not really, because it has been well and trult resolved.
The vast majority of mammals in Australia are not and never have been macropods. So in what way is there any lack of competition?
Let’s see. They filled the niche of medium sized browsers and… well that’s it. The tree kangaroos have adopted arboreal sleeping arranngements, but they remain medium sized browsers. Even those few macropods that adopted an omnivorous lifestyle were forced to abandon saltatory movement.
So the hoppers filled exactly one niche.
In what way did hopping macropods fill many niches? The ungulates filled many more niches than the macropods ever have, existing as browsers, omnivores, aquatic herbivores and carnivores, in medium, large and fricken’ huge sizes.
In fact can you give us an example of any other mammal group at all that is more conservative than the macropods (assuming comparable or higher levels of richness)?
No.
First off both modes of digestion have their advantages and disadvantages and perissodactyls will outcompete ruminants in many situations. Which is why the two groups coexist worldwide. The perissodactyls still comprise ~20% of the world’s medium and large gazing animals and around 30% of the large animals. So it’s not like they are uncompetitive.
The true disadvantage of the perissodactyls seems to have been there susceptibility to human hunting, probably because they are better suited to life as huge animals. Prior to human influence they comprised about 25% of the large grazing fauna of the world by numbers, and about 70% of the “huge” animals".
No, it’s so much more complex than this that the statement you made is almost completely untrue.
OK, you know more about goats than I do. The placental mammal I’m most familiar with does not usually resorb the fetus, except for the apocryphal disappearing twin. Given sufficient stress, they may miscarry, but if we’re talking environmental problems in evolutionary history - exposure, starvation, chased by predators, etc. - at a certain point the female is more sitting duck for serious problems. Even before the evolution of doctors who didn’t believe in handwashing, death from childbirth was a common problem. As the prevalence of back-alley abortion deaths pre Roe-v-Wade demonstrated, getting rid of a fetus is by no means a simple task.
Marsupialism seems to solve 2 problems - allowing the female to jettison the child when necessary, but allow her to carry it far longer than would be feasible for a placental mammal. Since placental mammals seem to have won in most other places, odds are this is not a great advantage, or something else about placentals carries a bigger advantage.
I’m not sure I understand. The little I’ve been able to find suggests that all kangaroos evolved over the last 25M years or so from potoroines; a little critter similar to a potoroo (hence the type name?) These little 2-foot hoppers (macropods) evolved somehow from a small, 4-legged hopping and scurrying precursor. Somewhere in their development, 2-legged hopping became more efficient. I’ve found some description that suggests hopping is more efficient because the tendons act like elastics - an interesting development.
So tiny hoppers expand to fill a large number of niches - how is this different from what I said?
They were successful. The question is why? The likely answer, from what I’ve been able to find, is that the climate of Australia changed drastically - creating new ecological niches where, presumably they could outperform anything else competeing for that niche. The island geography prevented alternatives from migrating in and taking over the niche before they better filled it. They vary in size and range, from the desert to the forest, ground and tree. That’s variety.
Was everything in Australia a kangaroo? No. For example, there is fossil evidence of one killer kangaroo, but generally they are herbivores. Similarly in other discussions, successful as ungulates may be, they are still generally herbivores. et cetera…
(I’ll bite. Which is a carnivorous hoofed mammal?)
Well, yes, you can write a book on the many details of the Theory of Evolution - come to think of it, that’s how the theory got started - but essentially it’s about differential breeding; finding the food to get there is the first and major step. Note how most animals are primarily defined by the food they eat and or the defensive strategies they employ to not be food in their environment.
But the falacy is - if we suggest that random mutations occur at a regular rate, provided that they do not affect ability to meet ecological demands, then both A and B will have the same change rate. If it doesn’t matter what fur or scales or colour and B’s pressures do not affect coloration or cover, both sets of genes are equally likely to wander in that regard. Only the B genes constrained by ecological pressures do not wander. I assume the variations tested for, that change regularly over time, are the unexpressed or “garbage” DNA sequences between productive genes.
So you’re trying to deduce the advantages of the macropod body plan by comparing it to humans. That is so invalid as to be ridiculous. Stick to comparing them to browsers of similar sizes and ecosystems.
The trouble with this hypothesis is that marsupials never faced those problems. Marsupials didn’t evolve from placentals, they evolved form monotreme like ancestors. So obviously these can not be the problems that Marsupialism evolved to solve.Traits can not evolve to pre-empt problems that never existed.
No, as we have already explained in some detail, there is absolutely no evidence at all that placentals have any advantage at all, and considerable evidence that they lack any advantage.
The most widely held belief is that the placentals came to dominate simply due to random chance. If two groups of organisms compete then necessarily one must become extinct. There is a 50/50 chance of either group succeeding. At the time that the mammals were ascending there were three main land masses: Euramerica and Africa, Australasia and South America. The placentals dominated Euramerica, the marsupials dominated Australasia and South America was dominated by marsupial carnivores and placental herbivores. This is precisely the outcome we would expect if there was neithe rgrpup had any advantage. It is precisely the opposite to what we would predict if placentals had any advantage.
As I’ve already said, these were not little critters as far as we can tell. they were medium sized critters in the 20 kg size range.
Not scurrying, no. The ancestor would have been a bounder, somewhat like a modern rabbit.
It’s no different at all. That;s the problem. You are repeating the same erroneous statments over and over.
The organisms in question weren’t tiny, and they never evolved to fill a large number of niches.
I ask you again: what niches have they evolved to fill? Complete this sentence: “Macropods started out as medium sized browsers and they have since radiated into alternative niches such as…”. And once agian I ask: what other group of mammals of comparble diversity has evolved to occupy fewer niches than the macropods?
That’s a tautology. All you are saying is that macropods adaptation allowed them to outperform competitors in the niche they occupied because they were able to adapt to outperform competitors in the niche they occupied.
It’s true enough. It’s equally true of ungulates and porcupines and duck-billed platypuses. It is so universally true that it is meaningless
Compared to what exactly?Once again I ask, what comparble group of mammals shows less variety? Rather than being remarkably diverse they appear to me to be remarkably conservative.
Well, no. The pigs for example are true omnivores and quite predatory.
You’re rather spoiled for choice, there were dozens if not hundreds of species. The most spectacular examples were the Mesonychid group.
No, it isn’t.
No, they aren’t. Name me a single classification system that primarily defines animals by the food they eat. Just one.
Of course they won’t.
No, they are not.
[quote]
Only the B genes constrained by ecological pressures do not wander./quote]
Right, now you’re getting it. And since we know that far more genes are constrained in this manner for population B, are they going to have more or less genetic drift?
Look, md2000, at this juncture I really don’t have much faith that you have a clue what you are talking about. You keep repeating the same erroneous statements that have already been pointed out as erroneous. You are attempting ridiculous comparison, you make several factually incorrect statements in every post and you refuse to answer basic question.
If you don’t start answering questions and proving some evidence for your more controversial claims I;m going to wash my hands of you and leave others to decide the worth of your claims.
Arguing with someone who brings nothing to the table but factually incorrect assertions is fruitless.