Hard SF : Psychic Powers & Fringe Theories : Telepathy & Evolution
Could an intelligent species have the capability to communicate by telepathy? The possibilities depend on how we define our terms. There seems little scientific reason why intelligent beings couldn't learn enough about their neurology and electronics to be able to surgically add brain implants that would connect their brain's language centers to something like a cell phone network. Or bio-engineer a new body organ for short-range radio communications. But this is hardly what one usually means by "telepathy". For the purposes of this site, we will not seriously consider supernatural means or anything without a physical foundation. If we mean "could a species naturally evolve an organic means of mind-to-mind communication," there are a number of issues involved.
First, let us consider how evolution works and can develop means of communication. Evolution moves ahead in stages. Early life forms with no vision would not simply in one leap get eyeballs, optic nerves and a visual cortex. They would develop a light-sensitive membrane that would provide light and shadow perception, then progressively get better membranes, protective covering for the membrane, a protective covering with lens capability, a dedicated section of the brain as the "eye" becomes capable of capturing more detailed imagery, etc.
In addition to seeing, hearing has considerable benefits. Sound is a convenient phenomena to be able to detect. A rock falling makes a sound. A twig snapping when it is stepped on makes a sound. Water gurgling in a stream makes a sound. Hearing these things can be useful, and it is possible to hear such things even if one can't see its source - it can provide you with information seeing may not. Once hearing evolves for these functions, animals may develop an ability to make their own sounds to tell their fellow herd members of danger, to help parent and child animal find each other, attract mates, etc. The first danger calls made by animals presumably didn't begin with one yelling "Hey guys! Danger is coming!" with the other animals saying, "Joe says danger is coming!" It probably began as something more like one animal grunting, "Yikes!" and the other animals looking up to see where the "Yikes" came from and noticing the danger purely incidentally. But that was an advantage, so it was passed down and expanded on. Animal calls became more developed and eventually human speech emerged.
To give another example of how evolution works in steps, consider human tool use. To handle tools, humans need hands on arms. Hominids didn't simply start as quadrupeds, then decide it would be a neat idea to have arms / hands, and start walking on their hind legs. We have arms because we evolved from arboreal creatures that used arms and hands for climbing, swinging, etc. Although our ancestors had to go through an arboreal period to develop arms, the extent of our tool use and technological development required hominids to become ground-living. Both steps involved practical, physical conditions.
Within this kind of framework, we need to ask how something like telepathy might evolve. For instance:
(1) Suppose you have a planet on which there are natural sources of radio emissions that are associated with some sort of survival value. Maybe the radio emissions come from areas with harmful radiation and it is useful to know to avoid those areas. Animals on that planet might evolve a radio equivalent of ears to detect this. Later, some animals might evolve an ability to give off radio waves to scare away predators who would be tricked into thinking they were near a radiation area. Later, animals with both an ability to "hear" and emit radio might develop a language using radio.
(2) If it were possible for life to evolve in a vacuum, hearing and speech via sound waves would not be an option. Something like radar and radio might develop to serve similar functions. Step by step, a radio language might emerge.
These are the types of practical factors that might make radio "telepathy" possible. However, under Earth-like conditions, there may not be the necessary stepping stones to build all that would be needed. Any plausible evolution of telepathy would have to have a similar practical basis, which does not seem to be present for humans.
There is one other issue that is worth considering when pondering the likelihood of telepathy as it is commonly portrayed in fiction. While one may occasionally find a story about a race of beings that communicate solely by telepathy, more commonly one reads about humans or other speaking beings who also use telepathy. This strikes me as unlikely.
Humans certainly don't communicate only by speech. Humans supplement their speech with gestures and other non-verbal means. Sometimes people even use gestures without speech in order to avoid being heard. However, the primary functions that hands and such evolved for have nothing to do with communication. They are unlikely to have evolved if their only purpose was non-verbal communication.
Nature would be very unlikely to develop telepathy in a species that already had speech, or to develop speech in a species that already had telepathy. Just as hands that evolved for other functions can be used secondarily for communications, a species with either speech or telepathy might develop some physiology for some non-communication purpose, which had some potential as a secondary means of communication.
The point is not that there would be absolutely no potential benefit from the second communication method, only that it would not give enough additional survival advantage to support its propagation. Perhaps, it's worth noting that while in our modern world communication beyond a reasonable distance for using sound has significant value, it would tend to have considerably less value for a group belonging to a social species living in a primitive state. (There are exceptions to every rule, but intelligent species are likely to be social and in their primitive state are unlikely to be a long distances from their group members.)
Even in a case where a second communication method evolved, after the second means of communication developed, the first means could become redundant and devolve. Maintaining both systems puts additional requirements on the body, possibly giving an advantage to individuals who lack the less beneficial of the two kinds of communication.
If we encounter telepathic aliens, they will probably not speak as well.
Where sound is possible, it seems the evolutionary efficiency and benefits of hearing sound will probably promote it. And further evolution will be built on that. If there isn't significant environmental radio emissions, there is unlikely to be enough benefit from sensing radio to prevent hearing from getting a substantial head start. Once hearing is well established, communication using hearing can develop. When these means based on sound are already in use, it becomes more difficult for any first steps using radio to show clear enough advantage for it to grow in the gene pool.
Assuming an intelligent species does not evolve considerably different than most Earth species, we can expect that prior to industrialization most members of their species will live in a relatively close proximity to family and friends they may need to communicate with. Although there certainly were human travelers before our industrial period, they would seem to be a far too small part of the population to play a role in evolution. Also, individuals distant from one another would seem to be less likely to be able to communicate information that would have survival value to each other. Being able to transmit and receive over longer distances would require investing more body resources into maintaining the body parts involved, so there would have to be sufficient benefit to justify the cost. As a result, it is most likely that if telepathy evolved, it would function within a reasonable radius to reach family and friends over a limited area.
Assuming this species has a relatively small number of generations between the advent of greater travel and the advent of telecommunications, there would not be time to evolve telepathy for a longer range before the need was eliminated by technology. (Our speech has a limited distance range beyond which we must use technology to extend that range with telephones and other devices. They would use technologies appropriate for them.)
Therefore, even if we encounter a species with a telepathic ability, it may only reach over a relatively short distance.
[It may be that whales, by the nature of their size and resulting territorial range, might have a reason to communicate over a longer distance. This is a practical consideration, we should not expect long distance just because it would be a cool idea.]