OK. You managed the last one, try this.
Why have humans got five digits?
I presume there must have been some evolutionary advantages at some time, but…
For a detailed essay on this specific questions, I refer you to the book “Eight Little Piggies” by Stephen Jay Gould. The book takes it’s name from an essay about why virtually all terrestrial vertebrates have, or descended from ancestors who had, five digits.
In a nutshell, if I recall the gist of it correctly, early land vertebrates had varying number of digits, anywhere from three to eight. During the Permian/Triassic extinction, however, an estimated 96% of all species were wiped out, including entire orders of animals. The few species of terrestrial vertebrates that survived happened to have had five digits to pass on to their descendants. So five digits is simply a matter of luck of the draw, or historical contingency. Whenever there is a mass extinction, a whole lot of evolution by natural selection seems to go out the window.
Barely off-topic, but I’ve been told that our evolution is taking away our pinky/smallest finger, and that past generations’ have been longer. Is that true? Will we in a million years have only 4 functional fingers?
Well, first off, evolution does not really allow for forward prediction. Whatever random changes in genes occur will be influenced by the surrounding environment. Since we can predict neither gene mutation nor future environments, it is unlikely that we can predict the number of digits our descendants will possess.
As to the item that sparked your curiosity, I have never seen any article claiming a diminishing pinky. Certainly there is no current evolutionary advantage for an eight-fingered individual in a world that increasingly relies on keyboards.
I believe the Human evolutionary process has come to a halt. Natural selection doesn’t occur anymore in our society. To have an evolution, you need natural selection, you need to scrub off bad genes, but we’re allowing everyone to live, so there’s no more natural selection. Result, no more evolution. Diversity? sure, but evolution? no.
If evolution has come to a halt, how come:
(1) Average height is increasing
(2) Average breast size is increasing
(3) puberty is occuring early for girls (though this may be due to artifical hormones in the environment
There are two forces behind evolution: The struggle to survive, and the struggle to reproduce. In humans and domestic animals, the first is almost negligable, these days. This is what Ranma is referring to. However, the struggle to reproduce is still in full force, and can cause further evolution of things that may be attractive to the other sex. Breast size is probably a good example of something that could be affected by this, but the increase has been too rapid to attribute to evolutionary forces-- Diet is a more likely cause.
So, what changes can we expect to see? Whatever the next step is, it’s likely to either be inperceptible to the naked eye, or something that can happen gradually. Developing an extra finger, for instance, or losing one entirely, is unlikely, because it wouldn’t affect the nonexistant struggle for survival, and it would most likely have a negative effect, if any, on reproductive ability: A person with a different number of digits would likely be viewed as a freak by many, and would have a harder time getting a mate. A decrease in the size of the appendix, by contrast, is plausible: Nobody considers a shorter appendix a turn-off, and a person with a shorter appendix is slightly less likely to die of appendicitis. This is also something that can plausibly happen gradually, which is much easier than an abrupt change.
- better nutrition
- surgery
- better nutrition
Just joking on number 2. The effects of estrogen-like chemicals released to the environment could be an important reason. They could also be contributing to number 3, although this effect (earlier puberty) has been happening for about 100 years.
But evolution is likely to soon become self-directed, assuming that scientists can figure out how to permanently replace genes in the human genome. They haven’t quite gotten there yet.
Well, then maybe it’s artificial selection. :rolleyes:
If there were less selection, there would be more evolution. Selection inhibits evolution.
Besides, if a form doesn’t change, doesn’t mean there is no evolution. It means there is a great deal of selection favoring the older form. Just because cockroaches haven’t changed form much in over 250,000,000 years doesn’t mean that cockroach evolution has halted. It means that cockroach selection is favoring the 250,000,000 year old form.
Evolution is a law of nature, like gravity. You can’t stop it. You may relieve extreme pressures through adaptation, but if things change rapidly enough changes will follow. Squirrels are evolving no more at present than humans are, because they are as adapted to their environment as we are to ours.
The proposition you offer is usually stated: Environmental changes can be adapted to by humans through technology rather than physiological adaptation. But that is at best an approximation, not applicable to all cases. Our technological adaptation at present often involves the expenditure of energy via fossil fuels. If the earth’s climate gets warmer, what technology can we bring to bear? Run more air conditioners? If changes are extreme enough, we will evolve again, as will squirrels.
Besides, if humans adapt to environments through technology (or society), then those who adapt through technology (or society) BETTER will reproduce more successfully. You can’t get sidestep evolution.
What you’re saying is a bit ridiculous, considering that 2/3 of the Human population lives in under-developed countries. No computers there. What prevails there is stamina(to survive debilitating diseases) and physical strength. Intelligence ain’t gonna save you there(may help, but that’s another thing). So we can say that there is still some form of natural selection in those countries. But in our society, we allow EVERYONE to live(and reproduce), so the gene pool can’t clean itself. People stricken with asthma wouldn’t have survived 200 years ago, but now, they are allowed to thrive. The smartest thing to do would be to pick only the best genes out of the pool, but that sure isn’t the most ethical… (BTW, I would certainly accept not to reproduce and adopt a child that has cleaner genes, but I know that there isn’t a lot of people that think this way…)
Natural selection is just one of many mechanisms at work as part of evolution. (e.g., sexual selection, genetic drift, mutation, recombination, gene flow)
or, perhaps humans will be a good example of punctuated equilibrium vs. gradual evolution
I thought we have five fingers so we can count to ten easily.