Why are some animals practically indistinguishable from others of their kind and sex, while a few species such as humans, vary greatly by skin, hair and eye color, height, weight, shape of face, etc.? For example ducks seem to be carbon copies of one another. Why aren’t there Mallards with short, wide beaks, stubby wings, 12 inch legs and rings of green all down their necks?
Humans have evolved quickly according to the amount of sun, cold and sand they endure. Why haven’t ducks (or fish or reptiles) evolved or adapted this way?
This isn’t to ask about unusual mutations such as albinos, or interbred animals. Nor is the issue “personality”. It’s clear cats and birds that look much alike can have different personalities. The question is why “normal” humans seem to physically vary enormously compared to most other species.
[Q]“Ducks belong to the sub family Anatinae. Not only is this grouping the largest group of waterfowl it is also the most diverse. The characteristics generally held in common by ducks when compared to geese and swans are the small body size, shorter necks, narrower wings which are more pointed, and wing beats which are more rapid.”[/Q]
and
[Q]“Frequently the males and females are colored differently with the male having the brighter plumage of the two. There are two body molts per molting cycle. The most significant is the eclipse which is the cycle that takes place during the end of the breeding season that results in males and females looking almost identical. Another characteristic is the speculum which is produced by the bright metallic feathering of the secondary feathers. There are also voice differences between the male and the female.”[/Q]
There are plenty of pictures of various ducks. Perhaps I have misunderstood the question, but this tells me there is more variation in ducks than humans.
I would guess it is because humans inhabit a huge range of environments while ducks (of a particular species) are found in pretty much a single environment. Humans are really unique in that regard. I can’t think of any other species of land animal that makes it’s permenant home in the tropics, the arctic, and everywhere in between.
If your are referring to variation within a particular species of duck (or bird in general) I would venture to say it is mainly because ducks have a more relatively uniform environment (ie there are no “desert mallards” or “mountain mallards” or “savannah mallards” and so there is less need to have the physical differentiation that tool using monkeys would require (ie differing skin color, hair type and body topographies) to adapt to a wider range of environmental challenges.
With respect to the relative uniformity of a “duck look”
for mallards I would venture to say that to a trained ornithologist (or another duck) there would be significant differences between mallard ducks of the same sex but like any set that we are not trained to differentiate “they all look the same to us”. I remember a study done years ago that looked at the difference between ethnic groups (IIRC Af Am, whites and asians) and how accurately they could recognize differences between individuals in other ethnic groups. All groups did about equally badly and all were truly surprised that the other groups couldn’t see these obvious differences between people of their respective race(s)
.
A duck may not have been the greatest example, since it can move to any environment it wants.
I was thinking about the difference of type between the environments of humans, and say, rats. It seems to me like a common rat is pretty much the same whether it lives in Canada or Mexico. Whereas aborigine humans from those areas vary considerably. Maybe the rat, for example, is just a more adaptable (or less sensitive) mechanism that doesn’t need to change its skin color, eye pigment?
Oh, you’re thinking along the lines of eye and skin color? How about coat color, if we’re talking mammals? There are brown rats, grey rats, white rats, multihued rats, etc, etc. Honestly, I think humans are not unusually diverse. We’re just trained to notice and identify variations in humans and not in other species.
Actually, I’ve always wondered this in respect to cats and dogs.
Cats are pretty similar in size and face shape, really. Hundreds of breeds mean long hair, short hair, and colour variation, but really cats are almost all cat-sized.
But dogs, on the other hand, are so wide and extreme in variety - from extremely huge to extremely tiny, and each with distinctive additions like tails and ears and muzzles all being quite distinct. And they can interbreed despite this!
Humans do have a very wide variation of facial features. It’s simple to tell one person from another.
This is probably because humans use sight more strongly than many other mammals. We can’t differentiate by smell. Sound is useful, but not if the other human isn’t talking. Thus if all humans had the same face, it would be difficult to tell friends from strangers.
It’s the same with chimpanzees.
Some species don’t need to differentiate, or can do so by smell or sound (birdsong), so their appearance is more uniform.
Overall I agree that
(1) Humans covered a broader range of environments than many animal species. Plus we travel a lot. An animal species may cover different areas but they usually keep to their areas and are defined (by us) as subspecies…such as the 8 subspecies of tigers (now down to 5 left) (or is it 5 down to 3? I forget at the moment.)
(2) Animal species do contain variations among individuals…it’s just that you do not notice them. Human brains are wired to notice variations in other humans. Go out and take some measurements of individual animals and you would start seeing variations within a species. Consider the “alpha male” fights among mammals. Who wins? The biggest/strongest/fastest. Variations!
Also
(3) Humans have more genes than some animal species (worms, insects, etc.) but we’re probably on-par in the gene count with other mammals (anyone know?).
Ducks do vary, and even to my untrained eye, there’s visible differences. F’rinstance, you know how male mallards have that greenish band around their neck? They’re not all the same color. Some are brighter or duller, and the hue can even be so far as purpleish.
Phobos – I don’t have numbers in front of me, but yes, humans do have about the same number of genes as most animals of similar complexity (i.e. vertebrates).
Otherwise, I agree that humans probably look pretty much alike to a duck. Probably easier to tell (unclothed) male from female humans but that’s probably another thread (or few) …
Does anyone know how genetic variation among humans stands compared to other mammals? There are a whole heck of a lot of humans, which would give a chance for a lot more overall variability; but on the other hand, humans are pretty well genetically mixed – I think bushmen and eskimos are more similar than grizzly bears in the rockies and grizzlies on Kodiak island, for instance (and much more similar than any given species of, say, oh, oak trees, to choose one of the pinnacles of evolution). Certainly no population of humans is even remotely coming close to becoming another species, unlike many, many, other animals.
Part of the question here is a matter of time. The dog has only been domesticated for 10,000-15,000 years ago. That is piddling time in evolutionary time. The rule of thumb that I’ve read for primates being separated long enough that they would not be able to breed is a million years.
Cats have only been domesticated half the time that dogs have so we just haven’t “fooled around” with them long enough to get the great differences we see in dogs.
Partly,
I guess you never owned ducks. I did, and didn’t have any trouble telling them apart, even though they were usually all of the same type. Male mallards do have different size throat bands, etc. Even the Peakings (you average white duck) do look enough different to tell them apart.
As for dogs and cats and the variety of sizes, what I’ve read is this(sorry, it was a borrowed animal book, so not title to offer): Dogs only seem to come in a greater variety of sizes. Cats vary more in size in nature (compare a Tiger to an ocelot, then a wolf to a coytote.) and they’ve been selectively bred down to about as small as possible. Even still, there are realatively large breeds like Ragdolls, or Maine Coon which are " 4 to 5 times larger than the Singapura, the smallest breed of cat. " (http://www.cats.alpha.pl/facts.htm)
Chronos and Elfkind: Agreed that ducks and clever human duck-watchers can tell ducks apart from another.
But why are there humans with: practically no noses, either huge ears at 90 degrees, or almost no ears, hair nearly everywhere vs. almost nowhere, practically no necks, legs 30% longer than average, etc., but not (as far as I know) ducks with no bills, no neck, no feathers, wings 30% larger than average, etc.?
It seems to me human genetics are somehow inherently more variable.
Something to keep in mind is that a lot of variation can also occur as a result of developmental processes. Consider the wide range of habits among expectant human mothers. Smoking, drinking alcohol, etc., can , of course, adversely affect the developing fetus. But beyond that, what the mother eats in general can have a pretty big impact, in terms of the nutrients provided.
Also, realize that for humans, we’ve got nine months, on average, of development, which is a lot of time for environmental influences to impose themselves on a developing fetus.
Contrast this with ducks (or birds in general, or, most animals in even-more-general). The time from fertilization to cute little chicky is much shorter. Because of the whole egg thing, the environment of the developing fetus tends to be somewhat more stable, and even before the egg is laid, the dietary habits of most ducks of a given species are not terribly varied. As a result, gross variation (such as adult body size, wing length, leg length, neck length and so on) is likely to be less pronounced than in humans.
Of course, some variation does occur, and, indeed is necessary for evolution in general.
The above is grossly generalized and simplified, of course. I’m no expert in fetal development, so I don’t know all the particulars. But I do know that there’s more to individual variation than what’s in the genes.
First of all, humans have specialized areas of their brain specifically wired for the recognition of human faces. Some people with small strokes retain essentially perfect visual acuity, except they can’t tell one face from another.
Second, dogs. Dog breeding is much easier to control than cat breeding, especially the way cats were kept up until the 20th century. Cats came and went as they pleased, and mated as they pleased, meaning all cats were random-bred. Dog breeding was much easier to control, and dogs could be bred for various traits.
The African Wildcat is pretty much the same size as the domestic cat, there hasn’t been much breeding for size. But domestic cats are already dwarfed…they are one of the smallest members of the Felidae.
Oh, and cougars/pumas are an example of a species that exists from the sub-arctic of Alaska and Canada, through the temperate grasslands and forests of the lower 48, through the deserts and savannahs of Mexico, through the rainforests and mountains of Central and South America, down to the pampas grasslands of Argentina, to the sub-arctic (OK, sub antarctic) of Patagonia. Pretty much every area of North and South America is or was occupied by cougars.
And basically, the OP is not giving animals enough credit for variation. Many many animals are so different that they are given sub-species status. However, all extant humans belong to the same sub-species, *Homo sapiens sapiens. * In fact, genetically humans are very uniform, having gone through a genetic bottleneck ~100,000 years ago. Most species are much more diverse, and have accumulated a lot more genetic diversity. It’s just that we don’t see the diversity. So one lizard has a slightly different scale count, or color, or length, or claw curvature than another lizard. Most people don’t notice and don’t care.
