Humans in hunter-gatherer societies have a shorter inter-birth interval than apes. Humans can give birth about every three years, chimpanzees only every five or more years.
Even though our babies are costly, we can produce more of them than our living Great Ape relatives. And when humans are done making babies, they actually survive for a long time. Our societies, long before medicine, the Industrial Age, or the farming age, allowed for grandmothers and grandfathers.
Interestingly, in evolutionary biology it is pretty much accepted that toward the end of the reproductive period, there is a minimal force of selection. But if you allow for cultural transmission, post-reproductive individuals can actually facilitate the survival of related, younger individuals, which opens up later stages in life to the action of natural selection. With regard to forming the next generation, what is striking is that to find strict monogamy in nonhuman primates, you need to look at the lesser apes, the Gibbons.
They live only in the forests in Southeast Asia. For humans, what is striking is that even though humans live in groups, pair bonding is a major phenomenon. This allows humans to participate in reciprocal exogamy, which essentially means exchanging mates across social groups. It allows for linking multiple kin lineages.
Now, if you combine the cognitive capacity of our slowly maturing children, the allomothering, and the input of the group into each child, a striking array of things becomes possible. It essentially allows for our social-cultural niche.
We share symbols. We have personal names. We have kinship terms, which allows for the formation of tribes. We have shared rituals, dance and music, sacred spaces, and group identity markers, and we can increase the capacity to cooperate with and compete against other groups.
I would like to provide you with an example or two of how a process may have led to the differentiation of humans from our closest relatives, and then talk about a cellular system that allows us to look at potential molecular and cellular differences that might have led to dissimilarities in who we are.
What we know is that the brain has increased in size across species during evolution along the branch that leads to humans. And we have come to the hypothesis that the growth of the brain is causally linked to what it is to be human.
The correlation is placed there because as the brain became larger, we acquired features that seemed more unique to the complexity in behavior that humans can exhibit. For example, when we think about what are the measures that allow us to examine how we may have evolved, we can use genetic information. Sometimes we obtain postmortem brain tissue from our closest ancestral relatives.
We can measure the magnitude of gyrations in the cortex and explore specific ideas or hypotheses about how they may be important. In addition, we have fossil crania to study and, from those skulls, we can build casts or make CT scans to get an idea of how the brain size was changing, again building our theories based on these measurements and the correlations that exist. Furthermore, we have cultural icons as well that give us an idea of how far a species had emerged, given its ability to build, plan, and generate art.
In each case, we have material that we can work with: genetic material, tissues, organs, and cultural artifacts. What has been missing, however, is living tissue from some of our lost ancestors and from our closest relatives, like chimps and bonobos. We have established a bank of cellular tissues from many of our closest relatives that allows us to look at distinctions between ourselves and our closest relatives.
As Pascal mentioned, chimpanzees and bonobos are our closest relatives, with 95 percent of our genomes being similar; yet, there are vast differences in phenotype. How can we begin to understand the cellular and molecular mechanisms responsible for these differences? One of the things we can do is take somatic cells, such as blood cells or skin cells, from all of our closest relatives. Through a process called reprogramming — by overexpression of certain genes in these cells — we can turn the skin or somatic cell into a primitive cell, called an induced pluripotent stem iPS cell.
These primitive cells are in a proliferating, living state that can be differentiated to form, in a dish, any cell of the body, allowing us, for the first time, to form living neurons or living heart cells from all of our closest relatives and then compare them across species. These iPS cells represent a primitive state of development prior to the germ cell. So any change detected in these iPS cells will be passed along to their progeny through the germ cell and into their living progeny.
Now a little bit of a disclaimer for those of us who work in this field: these cells have limitations. They are cells in culture. We cannot really look at social experience, and their relevance to a living organism is oftentimes questionable. But we can ask the question: are there differences that are detectable at a cellular and molecular level that help us understand the origin of humans? We have begun building a library with other collaborators around the world, and have reprogrammed somatic cells from many of these species into iPS cells.
They retain common features of embryonic stem cells at the cellular level and they have the same genetic makeup as predicted based on the species.
In our first attempt to see if we could identify differences in these primitive cells, we did what is called a complete transcriptional mRNA analysis. If we compare the transcriptional genomes of chimpanzees and bonobos, there are very few differences. So we pooled all our animals together and compared that combined nonhuman primate group to the human group.
In analyzing these genomes, we detected two very interesting genes. Why are we interested in these two proteins? These two proteins are active suppressors of the activity of what we call mobile elements, which are genetic elements that exist in all of our genomes. In fact, 50 percent of the DNA in human genomes is made up of these mobile elements molecular parasites of the genome. So what are mobile elements? They are elements that exist in specific locations in the genome and, through unique mechanisms, they can make copies of themselves and jump from one part of the genome to another.
Barbara McClintock discovered these elements through her work on maize. Some of us study a specific form of mobile elements called a LINE-1 retrotransposon. They exist in thousands of copies in the genome, as a DNA that makes a strand of RNA and then makes proteins that binds back onto the RNA, helping the element copy itself. This combination of mRNA and proteins then moves back into the nucleus where the DNA resides and pastes itself into the genome at a new location.
These LINE elements continue to be active in our genome, and they are particularly active in neural progenitor cells. Not only do humans make more of these proteins, but as an apparent consequence, the lower levels of these L1 suppressors in chimpanzees and bonobos means the L1 elements are much more active in chimpanzees and bonobos than in humans.
One of Dr. While we may not use them to forage for tasty termites like our primate relatives, they sure do come in handy for just about everything else! As children, we are taught to share. Did you know that chimpanzees share their food and tools? One of the earliest discoveries made by Jane Goodall was that chimpanzees hunt for meat. Just like humans, they do this in groups.
Like humans, chimpanzees use body language to communicate. They kiss, hug, pat each other on the back, hold hands and shake their fists. Chimpanzees not only communicate like humans, they also demonstrate a range of emotions including joy, sadness, fear and even empathy.
The Team Our Board. Read more about dating methods here. Among the major sources of evidence are sediment cores from the ocean bottom. They preserve the fossils of tiny organisms called foraminifera. By measuring oxygen in the skeletons of these organisms, scientists can calculate fluctuations in temperature and moisture over millions of years.
A lot! Since Darwin died in , findings from many fields have confirmed and greatly expanded on his ideas. Some members of both religious and scientific communities consider evolution to be opposed to religion. But others see no conflict between religion as a matter of faith and evolution as a matter of science.
Still others see a much stronger and constructive relationship between religious perspectives and evolution. Many religious leaders and organizations have stated that evolution is the best explanation for the wondrous variety of life on Earth. Many scientists are people of faith who see opportunities for respectful dialogue about the relationship between religion and science. Some people consider science and faith as two separate areas of human understanding that enrich their lives in different ways.
This Museum encourages visitors to explore new scientific findings and decide how these findings complement their ideas about the natural world. In science, gaps in knowledge are the driving force behind the ongoing study of the natural world and how it arose. The science of human origins is a vibrant field in which new discoveries continually add to our understanding of how we became human. You can learn about some of the most recent findings in this exhibit.
Societies worldwide express their beliefs through a wide diversity of stories about how humans came into being. These stories reflect the universal curiosity people have about our origins. For millennia, they have played a vital role in helping people develop an identity and an understanding of themselves as well as of their community.
This exhibit presents research and findings based on scientific methods that are distinct from these stories. Skip to main content. How does evolution work? What do scientists mean when they call evolution a theory? How does evolution explain complex organisms like humans?
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