How long has the average species lasted for?

[Simfish]

5 million years? 10 million years? I'm especially interested since the Pliocene was much warmer than today (with much higher sea levels), and it came only 5 million years ago.

 

[Ryan_m_b]

I remember hearing 5 million from an evolution professor at uni however I think he was referring to animals. Bacteria can obviously change much faster and some plant species have stayed the same for up to 15 million years

 

[Evo]

Well, sharks have existed for 400 million years.

Fossil records indicate that ancestors of modern sharks swam the seas over 400 million years ago, making them older than dinosaurs! Throughout time sharks have changed very little.

http://www.flmnh.ufl.edu/fish/education/questions/basics.html#existed

Opossums have been around 70-80 million years.

As the only marsupials found in North America, opossums have existed for 70–80 million years.

http://www.encyclopediaofarkansas.net/encyclopedia/entry-detail.aspx?entryID=5678

But Ryan remembers correctly

For example, given normal extinction rates species typically exist for 5–10 million years before going extinct.[7]

But there is no way of really knowing.

http://en.wikipedia.org/wiki/Background_extinction_rate#Measurement

 

[mishrashubham]

Well, sharks have existed for 400 million years.

While they have existed for 400 million years ago, they cannot be classified under a single species. However I might be wrong, in which case could you please tell the name of this species. I would really like to read about it.


Wikipedia gives an interesting table.
http://en.wikipedia.org/wiki/Background_extinction_rate#Lifespan_estimates

Interesting to note that average lifespan of mammals is only 1 million years.

 

[Borek]

There will be an obvious problem - we don't have good definition of what a species is. This is of particular concern when we have to deal with a dynamic situation of species turning into other species - without knowing where and how to split the line, we can't say how many sections it has.

 

[Ryan_m_b]

There will be an obvious problem - we don't have good definition of what a species is. This is of particular concern when we have to deal with a dynamic situation of species turning into other species - without knowing where and how to split the line, we can't say how many sections it has.

It's not that we don't have a great definition of species per se, it's that there is no real thing. 'Species' is an arbitrary way for us to distinguish between organisms by placing them into groups.

 

[bobze]

It's not that we don't have a great definition of species per se, it's that there is no real thing. 'Species' is an arbitrary way for us to distinguish between organisms by placing them into groups.

More of this please :tongue2:. Its one of the hardest things for people to wrap their head around about evolutionary biology. Consider that if there wasn't extinction, we'd (collectively, all organisms on earth) be the same "species". Without the gift of hindsight and incompleteness in the fossil record, we would be unable to draw arbitrary lines in the sand and say "everything on this side is species one, everything on the other is species two".

 

[mishrashubham]

There will be an obvious problem - we don't have good definition of what a species is. This is of particular concern when we have to deal with a dynamic situation of species turning into other species - without knowing where and how to split the line, we can't say how many sections it has.

I thought we did have a proper definition. But I understand, while it would be easy to say that a species has gone extinct, drawing a line to show that a new species has emerged would be difficult.

 

[mishrashubham]

Consider that if there wasn't extinction, we'd (collectively, all organisms on earth) be the same "species". Without the gift of hindsight and incompleteness in the fossil record, we would be unable to draw arbitrary lines in the sand and say "everything on this side is species one, everything on the other is species two".

Sorry didn't get you.

 

[Borek]

It's not that we don't have a great definition of species per se, it's that there is no real thing. 'Species' is an arbitrary way for us to distinguish between organisms by placing them into groups.

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

But it looks to me like we are just looking at different sides of the same coin.

 

[Pythagorean]

More of this please :tongue2:. Its one of the hardest things for people to wrap their head around about evolutionary biology. Consider that if there wasn't extinction, we'd (collectively, all organisms on earth) be the same "species". Without the gift of hindsight and incompleteness in the fossil record, we would be unable to draw arbitrary lines in the sand and say "everything on this side is species one, everything on the other is species two".

Groups of a such a unispecies could get isolated from each other and after some time exhibit clear speciation without extinction.

To be clear, we're only talking about species right? Not kingdom, family, etc?

 

[Phrak]

From http://en.wikipedia.org/wiki/Species#Definitions_of_species" is presented one amoung several definitions of species:

In the study of sexually reproducing organisms, where genetic material is shared through the process of reproduction, the ability of two organisms to interbreed and produce fertile offspring of both sexes is generally accepted as a simple indicator that the organisms share enough genes to be considered members of the same species. Thus a "species" is a group of interbreeding organisms.

This seems to good fit the question as it appears to have been intended. Yet the answer to the question in this form is not yet testable. Without resurrecting a shark from fossilized DNA, how do we know that the 50 million year old shark could reproduce with a shark of today, for instance?

 

[Ryan_m_b]

From http://en.wikipedia.org/wiki/Species#Definitions_of_species" is presented one amoung several definitions of species:


This seems to good fit the question as it appears to have been intended. Yet the answer to the question in this form is not yet testable. Without resurrecting a shark from fossilized DNA, how do we know that the 50 million year old shark could reproduce with a shark of today, for instance?

The problem get's worse when you consider the conditions under which things may not breed. In cases of sympatric speciation populations of organisms live in the same area but begin to speciate because they not longer breed (classic example is the hawthorn fly where there are two groups that could interbreed but prefer to mate on different fruits). It also reduces are ability to identify something as a species by requiring a test against all other groups. If we have two groups that choose not to mate and over time their gene pools diverge at what point can we say they were different species if we do not have data of them mating over that time?

Like many things in biology we need multiple imperfect definitions and tests to come up with the most useful explanation, with extinct/asexual species studies of morphology, genetics, location etc become more prominent

 

[bobze]

Sorry didn't get you.

Think about it like this (I find this analogy always helps people). Suppose I had this color bar representing an evolutionary lineage:

Now suppose I asked you to draw a line between red and orange. Where you draw the line and where I draw the line will probably be at two different RGB values. The reason being of course, the change from the "red species" to the "orange species" is very subtle--Its not a "click and where there" kind of thing. Rather it is an extremely gradual change in RGB values where a single pixel line (a "generation") is essentially (to us visually anyway) indistinguishable from the next.

Likewise, "species" are the same way. The variation vertically in anyone generation, is typically less than what is found within the population at large. Therefore, from parent to offspring (generation to generation) the distinction between "species" doesn't actually exist.

It only exists because the fossil record is incomplete (for example, we may have many "in between" generations missing between red and orange) and we are observing it in hindsight. Because of the incompleteness artefactual "divisions" can exist in a lineage--Which we call "species".

Consider another thought experiment put forth by Dick Dawkins. Which addresses the problems with the "biological species" concept and evolutionary lineage historicity.

Suppose you and I have a time machine and were off to collect historic ancestors in a manner rivaling the Victorian rape of the natural world. The ol' snatch and grab.

Suppose we dial our flux capacitor back to 10,000 BC and hop back through time.

[PLAIN]http://t1.gstatic.com/images?q=tbn:ANd9GcQV9wpCBWK5jCOo40cAhCAx22KahbsY6xfZA-TFxbD3zD3Rc1vYyQ

Abducting a person then bring them back to our future. In our sick experiment, we convince a modern individual to breed to this person from an ancestral population and see what happens.

Probably, we get offspring. So according to the biological species concept (we can interbreed--Simplified) we are of the same "species" as the individual from 10,000 BC.

No suppose we repeat our foray into history many times, hopping back in 10,000 year intervals. Eventually we run into an individual, well call individual X that cannot interbreed with us. So have we found an objective measure of our "species" its "ultimate origin"?

Consider the individual we abducted before X, we'll call Y. Individual Y, who we can interbreed with and is therefore "of our species" could very, very likely interbreed with individual X. In other words, individual Y's "X" is not the same as our "X", though both us and Y and still interbreed.

How then, can we have found a finite boundary to our species, when members we consider our "species" can interbreed with those "not of our species", while we cannot?

Species, much to the discomfort of even many professional biologists, aren't real tangible things---Lineages and populations are.

Groups of a such a unispecies could get isolated from each other and after some time exhibit clear speciation without extinction.

To be clear, we're only talking about species right? Not kingdom, family, etc?

Right and in evolutionary speak we call this "cladogenesis", where we have a lineage "split"--Parting ways for the rest of the existence.

But here is the kicker, the ancestral population--That is that 'real' ancestral population, with a specific frequency of alleles which gave rise to the two distinct populations is extinct. That population, even if they look the same, taste the same and smell the same no longer inhabits the earth. And because of this, we still have "extinction" which separates the two distinct forms and thus more forms cannot be produced from that hierarchical split in the lineage.

It's the answer to the creationist question "Why aren't there new phyla being produced?". Because, those populations which existed to give rise to the lineages we've deemed "phyla" have long since passed on this earth. Any "new forms" which arise from those distinct phyletic lineages will always be of a "kind" which descends from those lineages.

Looking at it another way; When will a "bacteria" evolve into something else? Bacteria describes a domain of organisms who's ancestral populations are no longer with us. Anything a bacteria "evolves into", no matter how strange looking, will always belong to the kind (in a more scientific verbiage: be seated in the nested set of) "bacteria".

 

[mishrashubham]

Thanks Bobze for elaborating; I understood what you said. Man, I seriously need to improve my English.