Brain transplant and personal identity

Daniel Dennett

In the previous post I wrote about brain transplants, but we must still consider the problem of how a brain transplant would affect our personal identity. Is our identity associated with the brain, and therefore would it be transferred to a different body in the case of a brain transplant? Or could something else happen?

In the first place, I must point out that this digression is not scientific, but philosophical, as for the time being a brain transplant is pure science fiction. It is not feasible now, and it does not seem probable that it will become so in a long time, assuming that it is possible to perform it successfully. This means that I am leaning on the void, the same thing I have criticized a few times when others do it...

In 1978, the American philosopher Daniel Dennett wrote a philosophical essay on this problem entitled Where am I?, where he used the science fiction genre to pose the problem of personal identity in the event of hypothetical scientific advances, such as the maintenance of an active living brain out of the body (although connected with it by wifi), or downloading the contents of a human brain into a computer.

Brain transplant

On February 13, 2017, the Spanish newspaper La Razón Digital published an interview with Rafael Matesanz, expert in transplants, with the following headline:

Brain transplant would be the panacea

As usual, the media prefer the most spectacular headlines, regardless of whether they misrepresent the meaning of the article. In this case, for example, the headline was taken from a rather secondary part of the interview. The following:

Is there an organ, today irreplaceable, but that will be [transplanted] in the future?

The brain.

Will it be viable?

To make it replaceable, we should know how to connect with the bone marrow the fibers leaving the central nervous system, otherwise... We are still far away, although we would like to be able to do it, for that would mean being able to cure quadriplegia and paraplegia.

...

Can you give me an example?

Consider what it would mean to people like Stephen Hawking, with a privileged brain, which you could transplant into a healthy body. Or many vegetative diseases that spoil the motor part of a body, with a healthy brain. It could be an unbeatable form of treatment, but we are far from it. Conceptually it would be the panacea.

Headlines and texts

Prehistoric pregnancy (Science News)

On several occasions I have criticized the distortion of scientific news by the media, especially the headlines, by saying things contradicted by the text, which apparently are more appealing. It seems that many journalists (at least those in charge of headlines) follow the old journalistic dictum, usually quoted in several forms, more or less equivalent, which, as is often the case with these lapidary phrases, has been attributed (probably apocryphally) to diverse personalities, such as William Randolph Hearst:

Do not let reality spoil a good headline (or a good report).

What I think regrettable is the fact that a magazine dedicated to scientific popularization, such as Science News, also falls in this trap of offering appealing headlines, which after reading the text can be seen not to correspond to the content. Let’s look at a few examples, offered during the week of February 19, 2017:

Intersex

Hermaphroditus,
wall painting from Herculaneum

In the previous post I mentioned that in biological chimeras (individuals formed by the fusion of two independent fertilized eggs) it may happen that most of the body belongs to one sex, but the genital organs belong to the other. This phenomenon is called pseudohermaphroditism. It can also be the case (although it is rarer) that the same individual has the two genital organs, complete or incomplete. This phenomenon was formerly called hermaphroditism, name of a son of Hermes and Aphrodite in Greek mythology, but these cases have recently been included in the concept of intersex, a more general term that covers all cases that do not fit the usual definition of male or female bodies, reserving the word hermaphroditism for animals or plants where that condition is normal.

To clarify things, normal members of the human species have 46 chromosomes (23 pairs), with pair 23 formed by the two sex chromosomes, which are responsible for the differences between the sexes. They can be either two X chromosomes (one inherited from the mother, the other from the father); this genetic endowment is called XX and the individual is female. Or they can be an X chromosome (inherited from the mother) and a Y chromosome (inherited from the father); this genetic endowment is called XY and the individual is male. But in addition to these two cases there are others, much less frequent. Let us quote a few (frequency figures are taken from Wikipedia):

Biological chimeras

A chimeric mouse with pups

Identical twins arise when a zygote (a fertilized egg) begins to divide. About five days after fertilization, it reaches the blastula stage and is implanted in the uterus, but for unclear reasons it can be broken into two separate parts, which will result in two independent embryos that may or not share the same placenta, although they usually have a different amniotic sac. The two siblings who are born share the same genetic endowment (the same DNA), except for possible post-separation mutations.

In contrast, two non-identical twins arise when two distinct eggs are fertilized, each by one spermatozoid, forming two different blastulas, each of which is implanted in the uterus through a placenta of its own. The two brothers will have different genetic endowments, similar to those of two non-twin brothers, because they come from different gametes.

But there is a third possibility: a chimera arises when two blastulas that would normally give rise to two non-identical twins merge before being implanted in the uterus and give rise to a single embryo and, consequently, to a single individual possessing, in different cells, two different genetic endowments. Thus, it may happen that a chimeric individual has (for example) the liver with a genetic endowment and the kidneys with another. Typically, chimeras are difficult to detect, unless (for example) just one of the blastulas would have given rise to an albino, in which case the resulting chimeric individual may have unequally pigmented skin. Even in this case, the cause could be different. It could also happen (although it is very rare) that one of the two zygotes is male (with X and Y chromosomes) and the other female (with XX chromosomes), in which case part of the cells of the chimera would be male and another part female.