If evolution is based on genes, then why don't we have a smear of animals?

[Hari_Seldon]

@naita

Have you looked at the topic of ring species? They are a smear, but at the ends of the ring they’re incompatible. They only exist due to a great geographical range of the species involved, and even then the whole ring is one particular kind of bird.

Here is what wiki has to say on the subject (in part)

Currently, there are four known forms of life that appear to be matching the definition of a ring species. The classic example is that of the Larus gull, which in 1925 was found to form a chain of varieties around the Arctic Circle by Jonathan Dwight, but lately doubts have arisen as to whether this is an actual ring species.[3] In 1938, Claud Buchanan Ticehurst hypothesized the Greenish Warbler spread from Nepal around the Tibetan Plateau, while adapting to each new environment, meeting again in Siberia where the ends could no longer interbreed.[4] These and other discoveries led Ernst Mayr to first formulate a theory on ring species in his 1942 study Systematics and the Origin of Species. Also in the 1940s, Robert C. Stebbins recognised the Ensatina around the Californian Central Valley as a ring species.[5] Finally in 2012, the first example of a ring species in plants was found in a Spurge form around the Caribbean Sea.

See Ring species - Wikipedia for the full account.

[njtt]

@TruCelt

. . ., all the genes someone has are genes that one or other of their parents had . . .

Change “had” to “carried.” Big difference. Not all the genes I express were expressed in my Mom. Some are not expressed in either of them, but since they both carried them, I now have those traits. The range of possibilities is much wider than what is observable in the parents. for example, I can taste things that neither of my parents can taste. they both had a recessive gene which expressed to create those receptors, and so chemicals that they happily and ignorantly swallow make certain processed foods repugnant to me.

I in no way said, or implied, that all the genes a person has (or carries, if you really think it makes a difference) are expressed.

[dasmoocher]

There is also crossing over and recombination of homologous chromosomes during meiosis and one could argue this creates “novel” genes if it occurs between different alleles.

The progeny could have an allele that did not exist in the parent.

[Wendell_Wagner]

An analogy can be made to dialect continua. There might be a range of language varieties over a long distance. The variety spoken in any one area might be quite similar to those spoken a short distance away, but the two varieties at the ends of the continuum could be so different that they are mutually unintelligible. So are the varieties in the continuum just dialects or different languages? The Wikipedia entry on this even compares it specifically to ring species:

Dialect continuum

[Endopotential]

@MrDibble

One individual unable to breed with its nearest relation is not a new species - just unlucky

Hmm, that could sum up the existence of some frat boys back in school…

But seriously, thanks all for some very educated replies. I guess the mark of a good question is that is just engenders more questions.

So could it be argued that among higher animals, sexual reproduction in a way slows down evolution? Sure it allows for the intermingling of genes (which greatly aids things forward), but still requires that the new “advancement” not be so profound that it prevents breeding with its peers.

Bad example, but say some Devonian frat boy fish miraculously sprouted lungs and legs and was ready to conquer the land. Awesome jump in evolution, but without a suitable mating partner, that advancement would be lost.

Sexual reproduction would seem to slow things down, requiring the the new mutant to slowly drag along its population in small steps. Steps small enough that it wouldn’t preclude interbreeding.

If frat boy fish were capable of asexual reproduction, it would have been able to charge ahead much faster.

And this is just for traits that are not intimately bound to reproduction. Seems that the closer your get to messing with the egg and sperm, the less leeway on evolutionary changes.

Am I off in this chain of thought?

[Colibri]

@Endopotential

So could it be argued that among higher animals, sexual reproduction in a way slows down evolution? Sure it allows for the intermingling of genes (which greatly aids things forward), but still requires that the new “advancement” not be so profound that it prevents breeding with its peers.

Most evolution is due to the recombination and selection of multiple existing mutations, not the spread of new mutations. While single mutations can spread rapidly in asexually reproducing organisms such as bacteria, there is no way to combine mutations in separate genes (or different mutations in the same gene) without some kind genetic exchange between different lineages (unless by chance multiple mutations occur in the same lineage).

[md2000]

@Colibri

Most evolution is due to the recombination and selection of multiple existing mutations, not the spread of new mutations. While single mutations can spread rapidly in asexually reproducing organisms such as bacteria, there is no way to combine mutations in separate genes (or different mutations in the same gene) without some kind genetic exchange between different lineages (unless by chance multiple mutations occur in the same lineage).

A classic example is Darwin’s finches. When the Beagle arrived, Darwin describes how the birds had no fear. One landed on an officer’s arm to drink the water he was pourng into a glass. After a few years of human occupation of the islands, one visitor describes a boy with a 4-foot stick collecting dinner, sitting quietly by a pool and whacking birds that landed there. They had learned to keep a bit of distance.

Presumably there’s a “skittish” gene. The birds that were too cautious fed worse when there were no predator threats, but survived better when the predators arrived. Selection was now picking the ones whose genes “turned on” more, to express this instinct. It’s not like they developed skittishness, just that the switch turned on to express this behaviour was selected for.

(one story has it this is where domestic cats and dogs came from. The wild animals that were less fearful would eat better off the bones and food discarded by early humans and so continue to follow them. Humans found them useful for some things (i.e. cats catch mice that are eating the grain) so they reinforced the cycle.)

[Learjeff]

@md2000

So the key is that in the environment they are in, species may have a variation but nature selects for certain characteristics.

Furthermore, “genetic drift” tends to even out the differences in a given population. Genetic drift is pretty well understood, characterized with fairly straightforward math, and a bit opposite of what it seems to mean, it tends to stabilize a population rather than change it. When there’s a novelty (either a new gene, or a change in environment), drift causes genes that confer a benefit to be spread through the population (rather quickly).

[reef_shark]

OP, there is a big difference between natural selection and molecules-to-man evolution. One is observed and the other is not.