RabbitWho said:
1. I mean for example why can't a kakapo fly? You could say flying is a waste of energy, but there's nothing wrong with a kakapo wasting his energy, flying is not a disadvantage, since he lives on an island with an abundance of food. So much food that to stop them eating it all they have somehow managed to evolve a system which stops them reproducing too often.
Is there a Darwinian explanation for this? If not does it suggest epigenetics?
I know quite often useless traits do not disappear. And I know sometimes you can evolve something that isn't necessarily helpful but that it keeps going anyway because it's not harmful. Then if you have a small population that turns into a large one (like with humans) you end up with lots of people having this useless trait because everyone is related to everyone else.
2. That's another question. How on Earth do you manage to evolve not to have too many offspringwhen you would think that if one parrot came along and had lots of chicks and the other came along and only had 4 in his whole lifetime that the one with lots would be the one that ended up taking over.. even though that's a really bad idea.
Edit: I was just thinking maybe sometime in the past there wasn't enough food and flying therefore because a big disadvantage. That's probably it. Thoughts?
Generally, evolution doesn’t completely eliminate physical features that are harmless but not useful. The function of the physical features can change or disappear, but the physical features remain in some form. The change in function of a physical feature isn’t strictly analogous to atrophy in the development of an individual.
The analogy with atrophy is misleading. Sometimes, muscle starts shrink in an individual due to disuse. However, populations don’t lose the ability to grow muscles due to disuse. In general, evolution causes an unused feature to show more physical diversity. This was noted by Charles Darwin in “Origin of the Species.” Because the feature isn’t used, the exact shape and size of the organ doesn’t matter. So if the feature is truly harmless, but useless, there will be a wider variety of shapes for that feature. There is no natural selection of shapes and sizes. Therefore, a truly useless feature would show even more diversity than a useful feature. The useless feature doesn’t really disappear from the population.
Changes in size, proportion and behavior could make the physical feature useless for its original function. The changes in size, proportion and behavior could be useful for some other function. Regulatory genes affect many physical features at the same time. Random changes in these genes produce disadvantages with regards to some functions, but advantages with respect to other functions. Even if the total affect is an increase in fitness, some functions will be removed.
A good example would be the kakapo. You didn’t mention the important fact that the kakapo still has wings. The wings are useless for flying, but they are still there. The wings have reduced wing muscles, and diminished keels. However, the wings haven’t disappeared.
The ancestors of the kakapo traded thermodynamic efficiency at the expense of flight abilities. With no predators, the main difficulty of a bird is finding food. Muscles use up energy, even when they are not being used. Wing muscles don’t get used by the kakapo, but they still make the bird hungry. So the reduction of wing muscles was a distinct advantage on this formerly isolated island.
Here is a link that shows you that the kakapo does have wings. However, evolution has changed its body so that it is more efficient in using the food it eats.
http://en.wikipedia.org/wiki/Kakapo
“The Kakapo is a large, rotund parrot; the male measures up to 60 cm (24 in) and weighs from 2 to 4 kg (4 to 9 lb) at maturity.[24] The Kakapo cannot fly, having short wings for its size and lacking the pronounced keel bone (sternum) that anchors the flight muscles of other birds. It uses its wings for balance, support, and to break its fall when leaping from trees. Unlike other land birds, the Kakapo can accumulate large amounts of body fat to store energy, making it the heaviest parrot.
Its anatomy typifies the tendency of bird evolution on oceanic islands, with few predators and abundant food: a generally robust physique, with accretion of thermodynamic efficiency at the expense of flight abilities, reduced wing muscles, and a diminished keel on the sternum.”
You didn’t mention that the kakapo needs a certain amount of land to call its own. The kakapo competes over land. They don’t fight over food. However, they do compete over mates. Juveniles often have foraging areas that overlap. So the resources aren’t unlimited as you suggest. So it is better for kakatos to be born heavy, and to be metabolically efficient, then to fly.
Here is an article that shows that kakapo do have home ranges. The males fight over track and bowl areas. There stick to their own areas, with a little overlap in feeding areas. The juveniles stick together within feeding areas. Therefore, there is competition between kakato.
Kakato didn’t have predators in the past, but they still had to compete for resources. Having loud voices to signal their location was obviously more important than flight, since this is how they mark out their turf.
http://researcharchive.lincoln.ac.nz/dspace/bitstream/10182/640/4/Whitehead_MSc.pdf.txt
Home ranges
An animal’s home range is not the whole area traversed in its life-time but the area used in its normal day to day activities that contains all the resources required for its survival (Krebs & Davies, 1996). Both male and female kakapo generally stay within similar home ranges much of the year, for a number of years, with some overlap occurring between feeding areas of individuals (Merton et al., 1984; Moorhouse & Powlesland, 1991; Powlesland et al., 1992). Kakapo are known to vocalise their whereabouts, perhaps to signal their presence to other kakapo, but they do not fight to defend their foraging areas so are not considered territorial (Powlesland et al., 1992). Some fighting does occur however between male kakapo over track and bowl mating areas (Powlesland et al., 2006). Kakapo are generally considered solitary (Higgins, 1999; Heather & Robertson, 2000) but recent evidence suggests that juveniles especially may forage in close proximity to each other with considerable overlap between home ranges (Farrimond, 2003). Adult males have also been observed roosting within short distances of each other (D. Eason, pers. comm.).
You seem to imply that if there are no predators, then the animal has no problems. However, food gets seriously limited.
Kakapo do sometime starve. They don’t breed when the food supply is low. Therefore, you are wrong. Thermodynamic efficiency is more important than flight to the kakato. The extra energy needed for strong wings could very well cause a kakapo to starve or stop breeding when the food supply is low.
Here is a link showing that kakapo stop breeding when their territories don’t have food.
http://www.nzes.org.nz/nzje/new_issues/NZJEcol36_1_64.pdf
Breeding variation in female kakapo (Strigops habroptilus) on Codfish Island in a year of low food supply
“ Multivariate analysis illustrates female kakapo were effectively partitioning available habitat, as breeders’ foraging locations were positively correlated with high-abundance rimu forest with a tall canopy, described as optimal breeding habitat. “
Combined with the fact that juvenile kakapo have overlapping foraging areas, it is apparent that having small family sizes can be an advantage in terms of kinship selection. A gene that limits the size of a brood may have an advantage because the brood forages together. Competition between siblings could reduce the frequency of that gene in the population.
There are a few exceptions where a feature disappeared in phylogenetic expression. However, very often the feature is still encoded in genes or chromosomes. The mutation may produce a regulatory gene that inhibits the growth of that feature, without changing the genetic code that contains the shape of the feature. The feature is hidden in the gene code, not eliminated. This is why there are atavistic mutations. A simple deletion of a regulatory gene can result in a physical feature coming back entirely. The genes didn’t go away, their expression was suppressed.
Ceteceans (whales, dolphins) are an example that I know well. Ceteceans evolved from a land based mammal sometime in the Eocene. The hind legs were a disadvantage in swimming, as they ruin the stream lining. Hind legs started to disappear. Some whales as late as the Oligocene had diminished hind legs. Today, no cetacean species normally has a hind flipper. There are some traces of a pelvis, but the pelvis is practically unnoticeable. The hind legs have vanished without turning into flippers. Or at least the hind leg phenotype has vanished.
There are mutant cetaceans that have a hind leg. A dolphin (Trusiops truncates) was recently found with hind flippers. The hind flippers were movable. The dolphin was sent to an aquarium in Japan. There have been whales caught with hind flippers.
Here is a link to an article on “vestigial organs”. Note that the majority of cetaceans no longer have hind legs or hind flippers. However, sometimes a cetacean is born with “complete” hind flippers. Evolution added genes to suppress the growth of hind limbs. The hind limbs didn’t disappear because of disuse. The regulatory genes “hide” the hind limb code because hind limbs are a disadvantage. Sometimes, a single mutation can bring the hind limbs back.
http://phylointelligence.com/bigbang.html
“In a few but well documented cases whales and dolphins have been found in the wild with larger hind legs.(Berzin 1972)(Hall 1984)(Sleptsov 1939)(Abel 1908)(Nemoto 1963)Some of these cases have even included feet and toe digits. To the left is a photo of the vestigial hind leg bones found in a humpback whale.(Andrews 1921) Additionally, as can be seen in the photo to the right, dolphins have also been found with full hind flippers. (Hidehiro and Ohsumi, 2008).”
Note that by my logic, the muscles could have disappeared altogether. However, that would be a very unlikely mutation. Once a complicated feature has evolved, it takes a lot of unlikely mutations to bring it back to the former state.
So you see that there is no "evolutionary atrophy." Sometimes, a feature is reduced because a reduced feature makes the offspring more fit.
