Scientific study turns understanding about evolution on its head

Jul 30, 2013
Latest research turns traditional 'V-shaped cone model' of evolution on its head

(Phys.org) —Our understanding of how animals on the planet evolved may be wrong, according to scientists at the University.

In a new paper, recently published in the Proceedings of the National Academy of Sciences, from the Department of Biology & Biochemistry looked at nearly one hundred fossil groups to test the notion that it takes groups of many millions of years to reach their maximum diversity of form.

Contrary to popular belief, not all animal groups continued to evolve fundamentally new morphologies through time. The majority actually achieved their greatest diversity of form (disparity) relatively early in their histories.

Lead researcher from the Department of Biology & Biochemistry, Dr Matthew Wills said: "This pattern, known as 'early high disparity', turns the traditional V-shaped cone model of evolution on its head. What is equally surprising in our findings is that groups of animals are likely to show early-high disparity regardless of when they originated over the last half a billion years. This isn't a phenomenon particularly associated with the first radiation of animals, or periods in the immediate wake of mass extinctions."

The team used published descriptions of extinct groups in order to construct 'morphospaces'; empirical spaces in which anatomically similar species plotted close together, and more dissimilar species plotted further apart. By looking at the manner in which the occupied 'volume' of space changed through time, they were able to track changes in morphological disparity.

Author Martin Hughes, continued: "Our work implies that there must be constraints on the range of forms within animal groups, and that these limits are often hit relatively early on. The only exceptions to the rule are groups that were wiped out at times of mass extinction. These groups tend to have 'flat topped' and 'top-heavy' evolutionary trajectories overall."

Co-author Dr Sylvain Gerber, added: "A key question now is what prevents groups from generating fundamentally new forms later on in their evolution. Equally intriguing is the manner in which some groups are able to break free from these constraints.

"Our results hint that this may hinge upon the evolution of new 'key innovations' that enable groups to exploit new resources or habitats, for example dinosaurs growing feathers and evolving wings or fish evolving legs and moving onto land to claim new territory."

Explore further: From minute to massive—mammal size evolution explained

More information: 'Clades reach highest morphological disparity early in their evolution', dx.doi.org/10.1073/pnas.1302642110

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User comments : 11

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antialias_physorg
4.4 / 5 (7) Jul 30, 2013
Sounds plausible. 'Key innovation' will open up an entirely new ecosystem (new food source, new mating availability, new potection from predators, or juts becoming a predator) to a species.
Such an unoccupied ecosystem will -because it is not under contention- allow a great variety of morphologies to survive (i.e. many more mutations are fit for survival than within a heavily contested ecosystem).

"A key question now is what prevents groups from generating fundamentally new forms later on in their evolution.

Maybe it works like this:
When the ecosyem is saturated to the point of sustainability then the weeding out starts. Radically new morphologies won't find a niche as readily and old ones will be refined rater than showing revolutionary new traits (maybe the old forms will even start to aggressively defend their niches against newcomers - which wasn't necessary until the saturation point was reached).

Until the whole thing starts over with the next key invention.
EyeNStein
1.9 / 5 (9) Jul 30, 2013
It is indeed highly plausible that a gene pool of high diversity and flexibility, with a wide selection of compatible breeding partners, would over time selectively stabilise any highly viable phenotypes which arose.
The genetic makeup of the most viable phenotypes (shapes and biochemistries) would necessarily protect itself against excessive random changes introduced at each mating cycle.
Over time, randomness in each species would disappear, and the ability to interbreed would be lost.
Without a genetic phenotype protection mechanism: The result would be a 'random walk' getting further away from the successful progenitor.
foolspoo
1.7 / 5 (12) Jul 30, 2013
our knowledge of this earth alone can barely fill the first page of this book
VendicarE
2 / 5 (6) Jul 30, 2013
The Evolutionary shape of diversity vs time will depend on the kind of environment provided to the organisms that are evolving.

What constitutes evolutionary change is also subjective since there are variations within species.

Beyond a rough vision, these facts make this entire thread of investigation essentially pointless.
EyeNStein
1 / 5 (7) Jul 30, 2013
Understanding the processes of this planet.
Understanding the obstacles and dangers as well as the benefits of manipulating biology.
Just for the thrill of increasing knowledge and decreasing the room for darkness or conjecture.
These are the reasons why this article and the comments (mostly) add benefit to humanity, and the quest for knowledge.
EyeNStein
1 / 5 (7) Jul 30, 2013
Not sure the blue solids are the best picture, except as a representation of generalised life-form diversity against time. The traditional 'tree' model, but with a bulbous (=diversity) and fractal branched trunk is more accurate but probably too complex for their purposes.
MrVibrating
1.9 / 5 (9) Jul 30, 2013
The findings seem consistent with McCarthy's Stabilisation theory..!
beleg
2 / 5 (4) Jul 30, 2013
One day humans will control their own shape of diversity. The shape you least expect.
You want to beat the present extinction fate/rate of 99.9% of all life forms.
Don't you?
Torbjorn_Larsson_OM
not rated yet Jul 31, 2013
Interesting. Gould's "punctuated equilibrium" takes another hit.

@VE: No, a main finding of the paper were only two types of diversity over time relationships: "Clades that terminate at one of the "big five" mass extinction events tend to have truncated trajectories, with a significantly top-heavy CG distribution overall. The remaining 63 clades show the opposite tendency, with a significantly bottom-heavy mean CG (relatively early high disparity)."

That is why the science was fruitful, it identifies generic facts.

@MV: "[claim]...!" Claim in need of reference and less punctuation.

@beleg: We can't beat extinction, since the average hominid species lifetime is ~ 2 million years. We are halfway to speciation already. (Or, some would argue, we did go extinct as 3 former subspecies when sapiens, neanderthals and denisovans merged and have started anew.)
Gmr
1 / 5 (5) Jul 31, 2013
What I don't see here is a comparison of similar timelines for totally different clades. Does one ascend in diversity while another reduces? Did one clades arrival supplant the former diversity of form of another? I'm not sure you can establish rules like this in a contextual vacuum.

If anything it says that some efficient forms haven't been outcompeted due to occupying a niche that is either hard to occupy for other lifeforms, or in a relatively stable area of the environment, or are enough of generalists to persist when other specialists fall away.
rufous
not rated yet Aug 02, 2013
Pacific salmon radiated over millions of years as the geomorphology of the ocean and river basins changed.
Some were stranded, some developed according to new submarine niches.
How does this compare to cichlids? The usual model?

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