What is your personal understanding of evolutionary success?
It was prompted by a comment thread on youtube regarding insect-biomimetic drones. A commenter asked why they’d bother wasting time on insects, when birds are superior, and ridiculed a response saying that insects are the most successful group of flying animals in existence.
I would say in evolutionary terms of course insects are - by multiple measures - species diversity, total biomass, length of survival of the class, this seems obvious. The flying capability of birds is irrelevant to their ‘success’ evolutionarily, their genes do not ‘care’ about their abilities.
But what is your definition of success?
With my own ideas there are several problems - species richness is affected by species complexes/splitting and species definition, survival time doesn’t consider the number of generations in that time, and biomass is affected by organism size.
Genes of course don’t care about those, the more copies, the sooner, the better. But it made me realise I don’t have a solid grasp of the idea.
From the gene’s perspective, the organism is just the vehicle to get the genetic material into the next generation. Whether bird or bug, morphologically simple or complex, if any lineage does that, it’s successful.
I have seen this expressed as, “A chicken is just an egg’s way of making another egg.”
Each of these can be considered a definition of success, largely depending on what questions are being asked. To get some perspective, think about what could be meant by an “evolutionary dead end.” Does it mean having no extant descendents? That would make pterosaurs an evolutionary dead end; but in their day, they achieved wide diversity of niches and morphologies and were the dominant flying vertebrates. They survived from the late Triassic to the late Cretaceous, a span of 162 million years, while birds have only been around for 72 million years. So, should pterosaurs be considered “less successful” than birds because they are all extinct now?
Or, let’s turn it the other way around. Humans are among the most widespread vertebrate species, occurring on every continent and most oceanic islands, and exerting such profound effects on their environment that they can bring about landscape-level changes. But humans are only 0.01% of all living biomass, whereas green plants comprise 80%; the genus Homo has existed for only about 2 million years, making it a recently evolved taxon, whereas the genus Equisetum has existed since the early Jurassic, thus pre-dating most of the dinosaurs and all flowering plants.
To give a slightly different take on what @jnstuart and @jasonhernandez74 have offered, for many years I have nurtured a concept that the ultimate role, the ultimate goal, of evolution is energy dispersal in the furtherance of the 2nd Law of Thermodynamics. In its simplest form, if you view every organism as just a bundle of energy, then the measures of “success” from an evolutionary standpoint would be: (1) population increase and dispersal, and/or (2) genotype/species diversification, and/or (3) lineage longevity. These three are obviously not mutually exclusive. In fact, the more a genetic lineage accomplishes any or all of these “goals”, I would argue that might be viewed as a measure of evolutionary success.
Wasn’t there evolution long before there were organisms with concepts of goals or success? Isn’t evolution just change over time? When is success measured–aren’t all types of organisms successful until they aren’t any longer?
In my opinion if animal didn’t go extinct it is successful and some animals are very successful in that regard. I think some insects might appeared before plants on land, but what do I know I’m not biologist
@sgene You seem to be thinking of “evolution” in a broader sense of the word. Certainly “change” is a type of evolution in that wider sense. But the OP is specifically talking about organic or biotic evolution.
If there’s one thing that I’ve learned since joining iNat, it’s that everything that is alive now or ever lived is an evolutionary success story.
Life is a collective success and we’re all just iterations of that process.
Maybe that’s why I always cringe when people use the word dinosaur to describe something that’s incapable of adapting, or… just a failure. As if humanity could manage cosmic asteroid impacts much better.
It doesn’t make sense to me to ascribe evolutionary success to broad taxa or even species.
In my opinion, evolutionary success can only be applied to an individual (or to a specific trait/phenotype) in the environment/niche it currently finds itself in:
A successful individual is an organism that produces more offspring than the median offspring of others¹ of its niche. (Technically, the offsprings offspring may be a better indicator than direct offspring².)
A successful trait is a phenotype which correlates (not necessarily causes) the organisms displaying it to have more “grandkids” than those in their niche which don’t.
If the environment changes, that can cause previously less successful individuals to become more successful and vice versa.
How long a species or taxon survives is more an indicator of the rate of change of the environment, less of success. Biodiversity similarly tells us more about the environment than the species itself.³ Biomass will usually negatively correlate with trophic level and body-size of the individuals.
So, success can also, IMO, not be compared between such different groups as insects and birds.
Edits:
1: usually the “others” in the same niche are members of the same species and population
2: producing infertile offspring is, in terms of evol. success, the same as producing no offspring
3: Variability of body-plan also plays a role. So more accurate would be longevity and biodiversity of a taxon are determined by the rate of environmental change vs. the rate of change in phenotype. In terms of biodiversity, segmentation will play a huge role as well. That’s why arthropoda contains so many very different body plans. Vertebrates and annelids are segmented too.
You can see Dawkins’ influence in a lot of the comments here. Whether you accept his ideas or not, they did change many biologists’ perspective of genes and their relationship to the organisms that contain them. I need to reread The Extended Phenotype.
This reminded me of the perspective from turtles because their success is a bit contextual. Turtles appeared in the fossil record in their current form about 320 million years ago. Yet there are only a couple hundred species (iNat currently lists 364 species), so by the metric of diversity they are clearly not so successful. But turtles live in nearly every environment on Earth and are nearly unchanged in all that time. Turtles are the only vertebrates with their shoulder girdle inside, not outside, the rib cage, a trick they accomplished developmentally by migrating the cells that are fated to become the should from outside to inside the ribs. They apparently did this early in their history and never bothered to change it. Whenever I look at fossils in Natural History Museums I’m struck by the fact their shoulders have the same struts as modern versions with the acetabulum bracing the top shell to create their distinctive shoulder anatomy. Apparently this allowed them the protective shell that both enabled and limited their life-history. The shell prevents the body cavity to expand during reproduction, so limited egg number each iteration of reproduction. The shell prevents the pelvis from expanding during egg laying, so eggs can only be as big as the fixed pelvic opening. Yet they are extremely long-live and usually take a really long time to mature. The fact that they hit upon this collection of traits (weird shoulder, non-expanding protective shell, delayed maturation, limited reproduction, long life span) and never bothered to modify it substantially (at least in terms of the shell/limb anatomy) makes them seem very successful if one overlooks the aforementioned lack of diversity. So successful, it seems, that once they hit upon this body plan they never needed to change it substantially. Apparently they’ve been ‘winning’ for this entire 320 million years with no need for evolutionary change. So who is more successful, the lineage that needs to constantly evolve to keep up with the environmental change or the lineage that figured out how to sidestep that change and just stayed the same?
Do chickens count as successful if there are 30 billion of them on Earth (easily the most abundant bird ever), spread across the entire planet, and they have secured grandchildren for perpetuity, at… certain costs? At least their wild ancestor is still around, unlike cattle.
I was thinking that when I think of a successful species my mind goes to the very versatile and adaptable invasive species like rats, House Sparrows, starlings and mynahs… But then it seems like in the current era the closer your association with humans the more successful you are. Until we stop having a use for them, like pigeons. They’re still hanging on pretty successfully though.
One of the more amazing things I have ever seen is how the brief early morning period when Passiflora blooms open in the garden falls perfectly during the low light period in which the Ptiloglossa bees fly and how those enormous bees are the only ones large enough to trigger the pollen falls from those flowers and how the pollen adheres to their furry backs as they travel from one flower to the next.
Plenty of other types of bees visit the Passiflora (Exhibit A, B, C), but the beauty of evolution is not on display in quite the same way. (They just look a little awkward trying to grab the pollen, frankly.)
Thank you! I know very little about turtles and your reply contains a bunch of interesting new information to me.
Regarding the age of a turtle-like body-plan (focusing mainly on “stereotypical” marine ones, as I’m more familiar with their life strategy than that of the other species), I think two factors may be very important:
Firstly, excluding juvenile stages and human predation, they seem largely unaffected by biotic factors, but their niche has very defined abiotic ones. Due to geological timescales being what they are (very big) this means their niche is only changing slowly if at all.
Secondly, evolving a turtle-like body-plan seems largely impossible for most modern taxa, so it is very unlikely for turtles to face competition in their niche, especially given their “head start” of about 320my, as you said.
Due to those reason, turtles just don’t face a lot of pressure and their body-plan stays largely the same.
Consider prions and viruses, the first RNA-- bacteria weren’t first, but they left a fossil record.The life forms that didn’t: well, we can only speculate.
Bacteria had already branched away from the Archaea; and the Miller-Urey experiments in 1953 (abiotic synthesis of biochemicals) showed the reliance of forming these compounds on appropriate conditions. End of the earth: meaning, total loss or binding/poisoning of CNOHP, complete irradiation, molten heat? Conditions have to be tolerable at some level for continuity of life as we know it.
