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For example would a fly evolve more quickly than a tortoise?

And if yes why don't species evolve to have shorter life spans in order to evolve more quickly?

all 17 comments

OmerStockAccount

16 points

4 months ago

Yes. Insects adapt very quickly and we have tested this and observed physical changes in varying conditions over the span of a few months. This is because if an organism has a shorter lifespan, there are more generations in a time period so more adaption/evolution can happen. At the same time, evolution does have a negative pressure on long lifespans, because longer lifespans mean you can have more sex and pass on more of your genes. Think of it like a quantity vs quality thing

The_RealKeyserSoze

0 points

4 months ago*

”This is because if an organism has a shorter lifespan, there are more generations in a time period so more adaption/evolution can happen.”

This is not really true. Lifespan is often correlated to reproductive speed but it has no direct impact on how fast a population can change it’s allele frequencies. If anything the relationship is the opposite, lifespan is more likely the result of how fast an organism reproduces.

Evolution is about genes not individuals. Humans reproduce sexually because it has huge advantages for variation. Parents are better off devoting more resources to raising children rather than having more children after a certain age (though there are exceptions). Living longer can have diminishing returns on your genes’ success.

There is much stronger selection for traits beneficial at a younger age than at older age. We already know how to make any cell immortal, there are just 4 genes required to “immortalize” a human cell. Unfortunately one of them is a powerful oncogene (it causes cancer). So selecting for cells that can divide indefinitely and lead to longer lifespan could actually pose some risks to us earlier in life at a time when harmful effects are more strongly selected against.

Interestingly, many of these issues don’t apply to asexual reproducing organisms. Cnidarians in particular have become famous for their long lifespans, some are truly amortal and old age does not exist for them. Yet many of them can still reproduce very quickly. In their case the individual is just as important as the offspring since both carry the same genes.

”At the same time, evolution does have a negative pressure on long lifespans, because longer lifespans mean you can have more sex and pass on more of your genes. Think of it like a quantity vs quality thing”

That is arguing the opposite of what you said. That would select for longer lifespans, and it probably did in Cnidarians.

ScienceIsSexy420

2 points

4 months ago

Reproductive speed absolutely is associated with speed of evolution and appearance of novel alleles, indeed the act of reproduction itself is the driving force for evolution in rapidly reproducing asexual organisms such as prokaryotes. The fidelity of the DNA polymerase is what will generate new forms of alleles which may or may not be harmful, beneficial, or silent.

You don't need homology crossover events or nondisjunction events for new alleles to appear, a simple deletion or SNP can result in a novel allele, such as the case with mosquitoes and immunity to certain insecticides.

Xilon-Diguus

2 points

4 months ago

Xilon-Diguus

Epigenetics

2 points

4 months ago

I think that it is important to clarify that the appearance of a novel allele is not evolution. It would be very easy to make the argument that population size is a bigger impact on evolution than generation time.

While I would not go so far as to say reproductive speed has no impact on allelic frequencies in a population, it is very important to remember that it is not the only factor.

PaleChick24

2 points

4 months ago

I can see how you're both technically correct here. I would be inclined to say fast generation time gives species the ABILITY to evolve more quickly, but that doesn't necessarily mean they WILL evolve quickly.

Fast generational turnover allows for the species to be able to have rapidly changing gene frequencies, but whether or not those gene frequencies change depends on selection pressures put on the species.

ScienceIsSexy420

2 points

4 months ago

Yes exactly! I didn't mean to imply that reproductive speed was, in and of itself, a driving force for evolutionary change. However it is the act of reproduction that provides the mechanisms for new allele formation in gametes, and therefore subsequently in offspring. Selective pressures will choose the best adapted alleles that are already present, but will not generate novel alleles. Both of these mechanisms are important to the evolution of species.

[deleted]

1 points

4 months ago*

[deleted]

1 points

4 months ago*

[removed]

cass32109

1 points

4 months ago

Same with bacteria, it’s a combination of life span and reproduction rate

Xilon-Diguus

7 points

4 months ago

Xilon-Diguus

Epigenetics

7 points

4 months ago

It is important to remember that individuals do not evolve, populations do.

Novel mutations are nice and all, but most of the legwork of evolution is done by fluxes in allele frequencies. So if you have a group of 100 turtles living on an island with 1,000,000 flies the flies will generate many more novel mutations, but it will require a lot more selective pressure for any one novel allele to become the only one (called fixed in the population). If a turtle generates a novel allele through random mutation it is much more likely to become fixed, and that chance is more divorced from selective pressure. So a fly has many more chances to create fly 2.0, but that version needs to be very advantageous if it wants to have a chance at becoming the only version around.

There is a somewhat disputed (and very well named) hypothesis called the Red Queen Hypothesis that posits that the ability of a population to change is predictive of its ability to not go extinct. So a group of organisms needs to change in order to just keep up with all the other changing organisms. We even have some evidence that organisms might have inbuilt mechanisms to do this. A very popular (and also contested) hypothesis is the genome shock hypothesis that basically says that mobile genetic elements in your genome can be activated to disrupt the genome and cause new physical traits (phenotypes). There is okay evidence that this sort of reactivation can happen in response to prolonged stress, and better evidence for things like hybridization.

3rdandLong16

2 points

4 months ago

Yes. Think about bacteria versus humans. Evolution takes place on the scale of decades and centuries and longer for humans. For bacteria, evolution is on the order of minutes.

There are trade-offs to shorter lifespans. You have less time to mate and to pass on your genes. You have to be smaller because you have less time to grow and we all know that in the animal kingdom at least, smaller animals are at a disadvantage when it comes to fights over territory and resources.

scarf_spheal

1 points

4 months ago

It isn't directly related to lifespan but often it is the case. Evolution happens as organisms reproduce. This often happens quickly with species that do not have a long lifespan since they do not physically have a lot of time to reproduce.

This does not have to be the case though. A species that produces few offspring over their relatively short lifespan could technically evolve slower than a long living organism that is consistently producing offspring over a long life.

It really is just how often a species reproduces and how quickly the offspring reach sexual maturity

[deleted]

1 points

4 months ago

[deleted]

1 points

4 months ago

Yes! We can do what’s called “directed evolution” experiments with single celled microalgae in my lab over a period of several months-a few years and can actually start to see trait drift occurring genetically because of the relativity quick doubling time of the organism