The Apologist

This is no attempt to commence a debate; I simply have some questions regarding evolution and I am curious to see how the evolutionists here respond.

How do you explain the evolution of the bat? How did wings gradually develop? It seems to me that incomplete, flightless wings would be quite detrimental to the mammal's survival. How did the bat proceed through the period in which it had defective wings?

How do you explain the evolution of the woodpecker? How did it incrementally develop the tough beak necessary to acquire arboreal sustenance? Obviously, hitting one's head against a tree can be fatal if one does not have sufficient means to breach the bark.

Finally, what are your opinions on the fact that humans do not use the entirety of their brains? Why did we evolve superfluous cerebral matter?

missus_gumby

I'm fairly sure we humans do use the entirety of our brains - but not 100% at any one moment. I think you may have latched on to some sort of popular misconception here.

It is interesting that you state the above as fact.

Martin

The Lone Ranger

The Apologist:

I'm on my way out right now, as it turns out, so I don't have the time to provide very detailed answers. I'm sure that others will show up to do so though; if not, I'll see what I can do tomorrow. So anyway, let's see:

Since there exist today flightless bats which use their wings to help them scramble along the ground (with quite a lot of agility, in some cases) and even climb trees, the claim that "flightless wings would be quite detrimental to the mammal's survival" doesn't seem to hold up all that well.

Quite a lot of bird species use their bills to pull, tear, or hammer the bark off trees in order to get at tasty insects. Nuthatches, for example, are quite adept at this. Woodpeckers are simply adapted to handle harder wood than most other bird species.

The claim that humans use only a small fraction of their brains is quite popular, for some reason, but untrue. Nowadays, it's possible to measure the metabolic activity of the various regions of a living brain, and this has demonstrated conclusively that the claim is untrue. I'd look up some references, but I really have to go for now.

Anyway, I hope that this was of some help.

'Night,

Michael

RufusAtticus

Which bat?

Which woodpecker?

Assuming that is true, why would God grant us superfluous cerebral matter?

~~RvFvS~~

[ May 29, 2002: Message edited by: RufusAtticus ]</p>

braces_for_impact

The bit about superflous brain matter and people not using the entirety of their brains is a common misconception. Ironically, it's a misquote of Albert Einstein.

lpetrich

Partially-functional wings are useful for gliding; consider what "flying" squirrels do.

Woodpeckers are clearly more specialized versions of birds that eat bugs that infest trees. Woodpecker adaptations enable them to reach deeper into an infested tree, enabling them to reach bugs that other birds could not.

An Urban Legend that most likely arose because much of our brains is without the easier-to-identify functions of being sensory and motor areas (receiving data from sensory nerves from the sense organs; sending commands to motor nerves to the muscles).

seebs

I don't know, but I believe some bats don't fly now... I don't know how they got there, or what the earlier phases were like.

I put it in the same category with whales who start growing teeth, then reabsorb them. (Only some whale species do this.)

Presumably by starting out on rotten wood; lots of birds get bugs out of rotten wood.

We didn't; that's not a fact, it's a popular myth.

parkdalian

Redundancy. Most parts of the body replace dead and injured tissues with new growth and scar tissue. This wouldn't work for the brain, otherwise we'd have a brand new brain every growth cycle.

Since there are no other ways to preserve memory other than redundancy in case of injury or aging, we evolved a larger brain mass as both added protection and for greater longevity. In case of brain injury and death of some neurons, surrounding, latent cells take over the function of the dead cells.

We essentially have evolved the brain of a much larger animal (with a longer lifespan or at least greater mental fidelity in old age) taking better advantage of our intellectual and cultural capabilities.

Imagine if we only lived twenty years. We'd have a much simpler culture because, obviously, no one individual would have time to acquire sophisticated expertise.

Although we have only recently been seeing average long life expectancies of 75-80 years, those stats refer to average lifespans including infant mortality, skewing the numbers.

However, the potential to have individual elders reach a ripe old age, even by today's standards, has existed for at least 250,000 years (the time period in which the homo sapiens brain reached its present size and form)

In preliterate societies, the elder folk were the the main source of cumulative technical and cultural knowledge and experience, so for that reason there may be a direct correlation between potential longevity and cultural sophistication.

More generally, the protective greater brain size may simply reflect our greater dependancy on our brain for survival.

There have been some studies linking brain weight to longevity in mammals and resistance to aging diseases in humans:


25. Graves AB; Mortimer JA; Larson EB; Wenzlow A; Bowen JD; McCormick WC. Head circumference as a measure of cognitive reserve. Association with severity of impairment in Alzheimer's disease. British Journal of Psychiatry, 1996 Jul, 169(1):86-92.

Abstract: BACKGROUND: Recent studies suggest that larger brain size may offer some protection against the clinical manifestations of Alzheimer's disease. However, this association has not been investigated in population-based studies. METHOD: The relationship between head circumference, a measure of premorbid brain size, and score on the Cognitive Abilities Screening Instrument (CASI) was studied in a population of 1985 Japanese-Americans aged 65+ living in King County, Washington, USA. RESULTS: After adjusting for age, sex and education, head circumference was positively associated with CASI score (b = 3.8, 95% Cl: 2.2, 5.4; P = 0.0000), but not with diagnosis of probable AD (odds ratio = 0.87, 95% Cl: 0.33, 1.87). When the data were stratified by AD status, no association was seen among controls (b = 1.6, 95% Cl: -1.7, 5.1; P = 0.4), whereas a strong effect was present among cases (b = 35.3, 95% Cl: 12.2, 68.4: P = 0.006). CONCLUSIONS: These results suggest that persons with AD with smaller head circumference either had the disease longer or progressed more rapidly than those with larger head circumference. Improvement in environmental factors in prenatal and early life that partially determine completed brain/head size may have consequences for the late-life expression of Alzheimer's disease in vulnerable individuals.

Di Sclafani V. Clark HW. Tolou-Shams M. Bloomer CW. Salas GA. Norman D. Fein G. PREMORBID BRAIN SIZE IS A DETERMINANT OF FUNCTIONAL RESERVE IN ABSTINENT CRACK-COCAINE AND CRACK-COCAINE-ALCOHOL-DEPENDENT ADULTS. Journal of the International Neuropsychological Society. 4(6):559-565, 1998 Nov.

Hofman, M. A. (1983) Energy metabolism, brain size, and longevity in mammals. Quarterly Review of Biology 58: 495-512

Vorkosigan

How do you explain the evolution of the bat? How did wings gradually develop? It seems to me that incomplete, flightless wings would be quite detrimental to the mammal's survival. How did the bat proceed through the period in which it had defective wings?

Obviously it never had "defective wings." It may have had smaller flaps of skin used for some other purpose. But, even 5% of a wing is useful if it enables you to survive and reproduce better than others of your species. Consider all the animals with half-wings -- ground-dwelling birds, flying squirrels and flying fish -- it is clear that half a wing is indeed better than none.

Vorkosigan

Oolon Colluphid

The bat? The order Chiroptera contains 986 species in 186 genera! So tell me... are they all one ‘kind’?

Erm, how about gradually? Arboreal creatures. Sometimes fall out of trees. Some survive by putting out arms (more surface area) and breaking fall. Ones with more surface area -- extra skin -- survive more often / survive falls from greater heights. Leave more descendants than those without this (initially slight) feature. ‘Slight’ is enough for natural selection to pick up on. More surface area of underarm skin --&gt; more descendants. Many examples in nature of gliding creatures: frogs, snakes, lizards, squirrels, marsupial ‘squirrels’, the ‘flying lemur’ (actually a gliding dermopteran), etc etc. As Buzz Lightyear would say, it’s not flying, it’s falling with style. Becomes means of locomotion. Note that bats drop from where they hang, then open wings.









See eg: <a href="http://www.life.umd.edu/classroom/bsci338m/Lectures/Gliding2001.html" target="_blank">Gliding: a common adaptation in mammals</a>

Once gliding, a flap of the arms can, if done right, carry the creature further than without. A second flap, further still.

Amounts of underarm skin, height fallen from and survived, number of flapping motions, distance covered, etc etc, are all things with smooth quantiative gradients that can be moved gradually along, each slight step being of slightly greater benefit to its owner.

See eg:
<a href="http://www.ucmp.berkeley.edu/vertebrates/flight/flightintro.html" target="_blank">Vertebrate flight</a>

“...not that I know anything about it, nor given it much thought...”

Ah, the old “what use is half a wing?” fallacy . 50% of a wing is precisely 1% better than a 49% wing for breaking your fall rather than you breaking your neck. And 49% is 1% better than 48%, and so on.

The ones with defective wings left no descendants. Only those that got it right at each slight step did.

Which of the 180 or so species of birds in the subfamily Picinae did you have in mind? The order Piciformes contains things like sapsuckers. Are they all one ‘kind’?

Is toughness of beak not something that could incrementally increase then? Might not some beaks be tougher than others? Might not birds with tougher beaks get more food than softer ones, and leave more descendants? Might not the toughness be genetic?

I suspect you might survive against a lamp-post. Birds, you may have noticed, peck. They may also probe and lever among eg bark. Softness of surfaces pecked can vary. Need I go on?

AFAIK, that is a fallacy, not a fact. Can you provide some evidence of its factuality please?

TTFN, Oolon