I am a layman but one criticism of the theory of evolution that seems sensible to me is the absence of intermediate forms.
For example types of ape that could mate with say gorillas and chimpanzees.
All the species seem very well defined when you'd expect a continuum.
However, imagine rabbits on an island. There are zillions of them everywhere and there is a wide variety of mutations. Mostly it doesn't matter because most of them can interbreed, and the ones that don't die out. But one day the rabbits get a terrible disease and almost all of them die. The ones that don't die have a mutation that makes them resistant to the disease. Now you have a different kind of rabbit where they are all resistant to the disease.
This keeps happening. Not always disease. Sometimes their food source disappears. Sometimes a new preditor arrives. Sometimes the weather changes. Each time, they almost all die. Only the ones that could survive live.
After all of that, the island rabbits are very specialised. They might not even be specialised for the current conditions. For example the disease may no longer exist. The weather may have changed back. The predators may have died out. But it doesn't matter. They are very different than the original rabbits, and also very different from the rabbits on the mainland. So much so that the two can't interbreed.
There is no intermediate forms because they all died. If they had not died, the specialised form would not have developed.
We can observe this both in the wild and in laboratory conditions. Especially with short lived insects (usually fruit flies) we can actually see evolution happening in this way. But with rabbits... we tried to kill all the rabbits in Australia with a disease and ended up with lots and lots of rabbits who are resistant to the disease.
This is why it is important to teach evolution in school.
The point is that as long as two minimally diverse populations remain in close contact and can interbreed, most of their mutations will cross the population boundary and we will probably classify them as one species, even though both populations may look nothing like their ancestors of 10,000 years earlier.
Mutations that prevent interbreeding usually don't occur in a single generation, they are the result of a long period of no interbreeding (and therefore divergent mutations).
Imagine a RGB LED that very slowly goes through the full color spectrum over a year. From day to day the colors would look almost identical to the point that you could swap them and no one would notice. You would probably call all the colors during January "red". Once you got into July you would call the colors "green" and would never be able to swap those hues with their "ancestors" from January.
This was a convoluted analogy to explain the concept of "gradual change", but hopefully it makes sense.
Here, you have a population whose geographic range is in the shape of a ring. Say, around the base of a mountain range. Members of the species may display some regional variation, but they can interbreed with their nearby kin. At some point on the ring though, there is a break. Here, regional variations will have accumulated to the point where the members are not able to interbreed and you have what appears to be two distinct, if similar, species. Only by following the line of population the long way around the ring do you find that the populations are still connected and actually the same species.
https://whyevolutionistrue.wordpress.com/2014/07/16/there-ar...
There are no known examples of ring species, which is a pity because it would be really cool.
It's a detail, but I think it's an important one. Evolution drivers do not have to kill most individuals. In fact, it does not have to kill any single one. Just a small decrease in fertility is enough to extinguish a genetic trait.
Killing a huge number of individuals does make it act faster, but is by no means necessary.
It absolutely is evolution, what it isn't is 'speciation'. For speciation to occur you would have to have enough reproductive isolation and enough time to allow for sufficient change - let's say in the range of thousands/millions of years, rather than a decade or two. Biologists will tell you anyway that the concept of a biological species is a bit hard to pin down anyway.
I don't quite understand your criticism regarding intermediate forms. There are many clusters of species where interbreeding is possible to some extent - Zeedonks, Ligers et all, not mention types of bluebell, dandelions etc. Moreover there are many many species where there are distinct varieties which are still similar enough to interbreed, but may be on their way to separating if given enough time and isolation.
Do not forget that the offspring itself also has to be fertile. Most hybrids aren't.
Yes. Evolution is just change in phenotypes over time. Speciation is a whole other ballgame, and there's no definitive answer as to what delineates species from one another. Some different species of fish will interbreed when forced together.
That is: Species are not well defined. They are only defined for human convenience, for categorization. But in reality, it's all one continuum. Interbreeding is only one factor in categorizing it. The big thing about being able to interbreed is chromosonal alignment, not necessarily whether they are differing species.
The humans of today aren't the same as the humans from 500 or 1,000 years ago. Prevalence of sickle-cell disease, lactose intolerance, skin pigmentation all these little things add up. If your substantiation of evolution consists of when speciation occurs, you're limiting yourself.
Take dog breeds for example. The changes we've implemented using the tool of evolution are drastic. What's to prevent this process from continuing? From eventually causing 'speciation', in the sense that two dog breeds can no longer interbreed? There are already subtle differences between dog breeds that make producing offspring difficult, and in the wild this difference would be magnified greatly.
A can mate with B, B can mate with C, but A can't mate with C.
Criticism of evolution isn't sensible, it's ignorant (which is fine). It's an observable phenomenon, each piece of which can be reasoned about without too much specialised knowledge.
Being ignorant about evolution is fine, and you asked politely and seem to have an open mind, so I don't think you should be downvoted. I think people are just a bit tired of creationists mis-using terms, lobbying, etc, so are sensitive on this topic.
I am not criticising evolution. I'm not qualified to do that. It seems like it is the best explanation yet to explain the diversity of life on this planet.
Personally, I attach no credibility whatsoever to the creationists' explanations.
I do think that people, even those of us who do not know a lot about it, should be entitled to ask questions without having our motives questioned. Indeed I thought that scientific theories should always be open to criticism. To say that one theory should not be, would be to elevate it to the status of dogma.
And if people are 'very sensitive' to criticism about a particular theory, there is more than one possible explanation for that. Another might be a frustrating lack of evidence. For example, in this thread 2 posters mentioned the existence of ring species and linked to the wikipedia page for that. That page has four examples but then goes on to suggest that there is doubt as to whether these are actually examples of ring species.
To re-iterate, I would bet that evolution is probably correct, however a degree of humility, not always evident, from its adherents would do no harm. The sun, it turned out, didn't orbit the earth.
This is typical, though. State a bunch of nonsense, then when called on it say you're just asking questions, people shouldn't be so harsh, and would it kill evolutionists to be a little more humble?
It takes a lot more effort to refute bullshit than to spew it. People naturally and rightfully get frustrated when people spew it.
As a result of reading the answers on this thread and other internet readings I still believe that there is a lack of intermediate species but I no longer consider that to be evidence against evolution.
If you consider my musings and questions as a bunch of nonsense and that I was stating them as facts and without humility, well I wouldn't agree with you.
They should be open to valid criticism, yes. But when their results are constantly under attack with baseless and unverifiable arguments, scientists grow weary and distrustful.
That page has four examples but then goes on to suggest that there is doubt as to whether these are actually examples of ring species.
This is an example of the kind of disingenuous arguments that evolution has to deal with; the page actually lists five examples, of which only two are disputed:
- The Larus gull, which may not fit the definition because there are subspecies that are not part of the ring (not because the existence of the ring itself is disputed).
- The Greenish warbler, which is not disputed.
- The Ensatina salamander, which is disputed. The page on the Ensatina itself suggests that there is interbreeding between all subspecies except for one, which suggests that it may actually be two separate species instead of a ring.
- The song sparrow, which is not disputed.
- The Tithymaloid splurge, which is not disputed.
https://whyevolutionistrue.wordpress.com/2014/07/16/there-ar...
Horses and Zebras are different species but can interbreed. Lions and Tigers can interbreed. https://en.wikipedia.org/wiki/Hybrid_(biology)
So the expected continuum you seek is totally there in tons of cases. It's just that there are cases where divergence gets too stark and intermediates die out.
When humans choose (for conceptual and communications' sake) to identify two very similar groups as different species versus different breeds, then we call mixes "hybrids" like this. When we think it's just a little too similar and we call them "breeds" of the same species, then we don't call mixes "hybrids" as often. This is just problems with the simiplisticness of language.
https://en.m.wikipedia.org/wiki/Ring_species
Living things evolve in groups which is why it's more common to have clearer lines between them, but it's not always like that.
https://whyevolutionistrue.wordpress.com/2014/07/16/there-ar...
I certainly wouldn't go around expecting them to make a baby based on what I've said, I just phrased things the way I did to try to emphasize the above point.
Of course, by definition they are different types of food, with the dividing line being 1.4% egg yolk solids. But one might notice that this dividing line is completely arbitrary, the universe doesn't care about it at all, and there is in fact a smooth continuum between "ice cream" and "frozen custard" and you can make food anywhere along that spectrum.
Some thing with species. Yes, chimps and gorillas are clearly different species according to how biologists define species. (There is some dispute over how exactly you define a species, because obvious definitions like "groups which interbreed to produce viable offspring" don't always produce sensible results, but chimps and gorillas are far outside the unclear areas.) But that doesn't mean that "species" is some inherent property in the world, it's just a useful device for categorizing it.
Moreover, recognizing that the theory of evolution does not really speak of "intermediate forms" but of common ancestors, would you be willing to label an extinct (but well preserved in the fossil record, including its DNA) species that is the common ancestor of two species as an intermediate form?
In other words, what would be the evidence for evolution to convince you of the reality of the theory?
I would just like to see more and more evidence as time goes by.
Physicists (and I'm not one of those either) seem to have a completely different attitude to evolution scientists.
Recently more evidence in support of einstein's relativity theory has been found, I believe. But they are still completely open to binning the theory if contradictory evidence appears.
There just seems to be an almost religious fervour around evolution that seems a bit unhealthy
Yes, not all evolutionary changes constitute changes of species.
> I am a layman but one criticism of the theory of evolution that seems sensible to me is the absence of intermediate forms.
An incomplete fossil record (and, given what is known about how the fossil record is laid down, its obviously going to be extremely incomplete even before considering how little of it we've actually been able to access) combined with evolution that is continuous (even if punctuated rather than constant-pace) is naturally going to miss lots of things between many of the things it preserves. That isn't a criticism of evolution.
> All the species seem very well defined when you'd expect a continuum.
There is a continuum; talking about it in any useful way, however, forces us to divide it up into discrete buckets -- taxonomic categories, whether "species" or higher- or lower-level categories -- and, where there are unclear cases, we end up arguing over which bucket they belong in, and how many buckets we should consider there to be.
Edit. If you want to know more then any of Richard Dawkins biology books are really good. The Blind Watchmaker would be my suggestion of where to start.
Does that answer your question?
Here's the first google hit with the phrase "absence of intermediate forms" you parroted, a site specifically dedicated to spreading misinformation about evolution -- Gary Bates' Creation Ministries International: http://creation.com/that-quote-about-the-missing-transitiona...
>Gary has been speaking on the creation/evolution issue since 1990. With a background in management and marketing, in 2002, he was invited to join the ministry full-time in Brisbane and eventually became its Head of Ministry. Much in demand for his popular lay talks on creation, Gary and his family relocated to America to serve as CEO of CMI-US. He was also elected to the position of CEO of CMI-Worldwide, CMI’s international Federation of ministries.
http://creationwiki.org/Gary_Bates
>Bates has a keen interest in the UFO phenomenon and wrote the Amazon.com top 50 bestseller Alien Intrusion: UFOs and the Evolution Connection. In July 2009 he was the keynote speaker at the first Christian symposium on the UFO phenomenon held in Roswell, New Mexico.
And here's a more reputable source that debunks the claim you parroted -- National Center for Science Education: http://ncse.com/creationism/analysis/transitional-fossils-ar...
>Fossils with transitional morphology are not rare. Fossils illustrating the gradual origin of humans, horses, rhinos, whales, seacows, mammals, birds, tetrapods, and various major Cambrian "phyla" have been discovered and are well-known to scientists. Explore Evolution's claims to the contrary are just a rehash of older creationist arguments on this point, relying on out-of-context quotes, confusion over terminology and classification, and ignoring inconvenient evidence.
What I asked you was why you were questioning somebody else motives, right after complaining that somebody was questioning your own motives? Is it OK to question people's motives, or not? Are you "entitled to ask questions without having our motives questioned" but nobody else is?
I think that it is OK to question if someone is being really charitable or helpful to you when they suggest that they are being so, in the context of what is otherwise a put-down.
On the other hand if someone asks a question about a scientific theory and has his or her motives for asking it scrutinised simply because the question implies doubt, then I don't think that's OK.