Does Evolution Happen Gradually or Suddenly?

Do new traits in evolution happen slowly, or all at once? Two new studies in the journal Science may finally help us solve this mystery.

Hosted by: Stefan Chin (he/him)
----------
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Adam Brainard, Alex Hackman, Ash, Benjamin Carleski, Bryan Cloer, charles george, Chris Mackey, Chris Peters, Christoph Schwanke, Christopher R Boucher, DrakoEsper, Eric Jensen, Friso, Garrett Galloway, Harrison Mills, J. Copen, Jaap Westera, Jason A Saslow, Jeffrey Mckishen, Jeremy Mattern, Kenny Wilson, Kevin Bealer, Kevin Knupp, Lyndsay Brown, Matt Curls, Michelle Dove, Piya Shedden, Rizwan Kassim, Sam Lutfi
----------
Looking for SciShow elsewhere on the internet?

#SciShow #science #education #learning #complexly
----------
Sources:

Image Sources:

[KBRoller]

I think the important bit a lot of people are overlooking is that if a trait isn't significantly harmful, it's basically got a 50/50 shot of sticking around just by random chance. So there's not always a pressure to keep something, as long as there's no pressure to lose it. And if a combination of neutral traits work together to become a beneficial system, then natural selection will start exerting the pressures to keep all of them together.

[_PM_]

Ever since I've heard of the bombardier beetle and how it has 2 separate storages for 2 separate chemicals, that are then combined at its rear end and turn into an explosive gas, I've been questioning how the heck did that thing evolve to have that.
Its Wikipedia page even has a section all about the evolution of this mechanism.

[evancombs]

It's a mix of both. Most of the time it is gradual, but sometimes when the circumstances are right it is relatively fast.

[gregboi]

Isn't an eye is a bad example of this, since you can have a very basic light receptor that is already useful without all the lenses and whistles

[mrpocock]

The eye is a really bad example for this, since we know so much about how it evolved intend incrementally. It is tempting to think that what some biology is selected for now is what it was selected for in the past, but that's not necessarily true.

[valarin]

The Phineas and Ferb reference at 5 minutes is hilarious. @Dantible

[talideon]

Oh, yeah, the eye is a really bad example. Not only have eyes evolved independently multiple times, and also the same kind of eye (octopuses and mammals have the same kind of eyes, but the former avoided having a blind spot), but every tiny increment along the way is beneficial and explainable. The only kind of vaguely puzzling thing about our eyes is the development of bands of muscle for focusing the lens, and even that's well understood!

[sazji]

The pitcher plant example has some flaws. It seems that the main function of the lid in most species is to keep rainwater from flooding the contents of the pitcher. That in itself is a valuable function. There are close to 180 species of Nepenthes, and though there are a few exceptions, most of them have lids that cover the mouth. (In a few species the lid serves other purposes, or almost no purpose at all.)

It also often serves as a “landing pad“ and, like most of the pitcher surface, also has nectar glands on it. it stands to reason that nectar glands on the underside of the lid are more useful toward luring the prey to the mouth of the pitcher. the “catapult” function seems to be sort of an extra added bonus, since it only functions when it’s raining. But if you already have a lid where insects would congregate and feed above the mouth of the pitcher, plants that caught more insects because of catapulting could end up producing more seed.

So there is really little likelihood of the lid “suddenly evolving toward a catapult;” instead, it seems perfectly logical but it would be a “fine-tuning” of lids that serve at least two functions.

[AdrianHereToHelp]

I would assume that eyes started as, like, some light sensing cells under the surface of the skin, and those just became more and more refined and specific because it turns out light's super useful

[bovanshi]

Evolutionary pressure is a scale related to how beneficial a trait is, on a range of scales directly or indirectly, for furthering those genes overall.

This means that even slightly disadvantagious traits can be passed on for a while in a population.

This negative trait can then be modified by further mutation and become beneficial in the end.

Neutral traits can spread unhindered in a population.

[chrisjohnson]

The lid of the pitcher is to keep rainwater out and filling the pitcher, making the pitcher too heavy to be supported, and it would dilute the digestive enzymes rendering them inert and unable to breakdown insects into a usable form.
The springboard is just a happy accident, insects take shelter from the rain on the underside of the leaf and getting knocked into the pitcher is a coincidence.

[joanhoffman]

In the late 1970s, there was a group of paleontologists who proposed the hypothesis of punctuated equilibrium (punc ec for short), in that evolution could happen in sudden rather than gradual changes.

[rezadaneshi]

Everyone of my ancestors fathers didn't look noticeably different from their sons, traced back from being human to an amoeba 4 billion years ago.

[BobMotster]

This episode wasn't as eye-opening as I hoped.

[Vort_tm]

Wait, we only just have a study on this? I remember discussing this in classes 20 years ago.

Eyes: start with being able to detect photos on tissue, select for better ability to perceive photons, select for a membrane to cover the area, select for ability to distinguish wavelengths of color, select for... you get the point.

Evolution is a slow process usually involving one change at a time, although much more rapid than we used to think with the validation of Lamarckism with DNA methylation. Natural selection would certainly benefit from synergy between separately evolved traits, but that's not a reason to suggest that any of it happened all at once.

[UnkillableMrStake]

5:00 you know it gets real when the science channel quotes Dr. Heinz Doofenshmirtz.

[devinnall]

Divergent Evolution could be a possible answer. Imagine if a population of pitcher plants was somehow separated from each other for a significant period of time and started evolving in two different directions. Then once they started developing their own unique mutations the two groups got reintroduced before they became completely separate species and by pure luck their traits were synergistic

[eriknicholas]

Ahh, A Phineas and Ferb reference, what an unexpected surprise. And by "unexpected", I mean...
COMPLETELY EXPECTED!!!

[williamtarleton]

Since the vast majority of past life on earth died without leaving any fossils or genetic information for us to find, it's amazing to me how much researchers are able ascertain about the (often ancient) evolutionary history of specific traits like these.

[lagautmd]

I had heard that punctuated equilibrium was one of the solid explanations for gradual and fast evolution. Gradual changes that broaden the gene pool conferring neutral traits that confer no advantage nor disadvantage. Then, a change in environment occurs, usually over a short period of time and some of these formerly neutral traits are significantly beneficial for reproduction compared to others. The other traits may survive in an area where the environment didn't change much, but for species in the changed area only the formerly neutral traits survive. Eventually, they become unable to interbreed due to gradual and punctuated changes.