Collaborative Research: Human Evolution, Rift Valley Environments, and Orbitally Forced Climate Change

探索人类进化的过程不仅仅是发现和描述早期人类的化石。为了理解导致直立行走、大大脑、工具制造和使用以及行为灵活性等关键人类特征的进化过程，有必要为这些创新发展一个背景。是什么样的环境力量塑造和指导了人类的进化？人类进化是早期原始人类与其物理和生物环境相互作用的结果，需要特别重建与原始人类发现相关的这些参数。然而，在陆地记录中以相关的规模记录古环境，并在进化和环境变化之间建立因果关系，仍然很困难。因此，人类进化的各个方面都是在海洋记录的环境数据的背景下解释的，海洋记录提供了大规模气候变化的详细记录。只有当全球或区域现象与当地原始人类生态系统的具体变化之间的联系能够得到证明时，这种方法才是有效的。该提案旨在通过审查一系列环境指标来直接解决这些问题，以便为东非大裂谷的人科动物序列制定一个高分辨率的古环境框架。这可能与全球气候变化有关。这项工作的重点是暴露在图根山（Tugen Hills）中的一个200 - 300万年前的沉积序列，图根山是肯尼亚巴林戈湖附近裂谷内的一个断层块。该序列显示了反映波动气候条件的主要淡水湖泊系统的突然和重复循环。在最近的研究中，该项目已经在这些短期振荡（每2.3万年一次）和米兰科维奇周期之间建立了明确的联系，米兰科维奇周期是由大气层顶部接收到的太阳辐射变化引起的，由地球轨道几何形状的变化控制。这些变化代表了地球气候系统随时间变化的主要驱动力，包括冰川-间冰期循环。36个脊椎动物化石地点，包括三个原始人类遗址，可以直接与这一序列相联系，提供了一个机会，以建立动物和植被对这些短期变化的反应模式。这项研究代表了开发多种环境和生态指标的首次尝试，这些指标可以直接与陆地裂谷背景下的米兰科维奇循环联系起来。这些数据将用于深入了解原始人类生态系统对过去600万年来非洲普遍存在的气候振荡的进化反应。虽然这些数据直接关系到Baringo盆地的化石人科动物及其脊椎动物群落，但将当地生态变化与轨道强迫的日照模式联系起来，提供了推断过去气候振荡对区域陆地生态系统影响的前景。有了这些数据，我们可以开始制定高分辨率的模型来解释气候和人类进化之间的相关性，并阐明环境变化作为哺乳动物进化，特别是人类进化的潜在驱动力的作用。这项研究将促进高度跨学科和协作研究，这对于发展进化与生态学之间多维联系的观点至关重要。这里概述的项目代表了一个理想的论坛，在其中产生和整合跨越传统上不同的学术学科的研究思路。这项研究将扩大机会，使肯尼亚国家博物馆的研究生和研究人员能够参与。

Exploring the course of human evolution extends beyond the discovery and description of the fossils of early humans. To understand the evolutionary processes that led to key human features such as upright walking, a large brain, tool manufacture and use, and behavioral flexibility, it is necessary to develop a context for these innovations. What were the environmental forces that shaped and directed human evolution? Human evolution is a consequence of the interactions of early hominids with their physical and biological surroundings and there is a need to specifically reconstruct these parameters in association with discoveries of hominids. Documenting paleoenvironments at a relevant scale in the terrestrial record and developing causal links between evolution and environmental change, however, remains difficult. As a result, aspects of human evolution have been interpreted in the context of environmental data from the marine record, which provide a detailed record of large scale climatic change. This approach is valid only if links between global or regional phenomena and specific shifts in local hominid ecosystems can be demonstrated. This proposal seeks to address directly these issues by examining a series of environmental indicators to develop a high-resolution paleoenvironmental framework for a hominid-bearing sequence in the East African Rift Valley. This can then be linked to global climate changes. The work has at its focus a 2-3 million year old sedimentary sequence exposed in the Tugen Hills, a fault block within the rift valley near Lake Baringo in Kenya. This sequence exhibits abrupt and repeated cycling of major freshwater lake systems reflecting fluctuating climatic conditions. In recent research, this project has established a clear link between these short term oscillations (every 23 thousand yrs) and Milankovitch cycles that result from variations in the solar radiation received at the top of the atmosphere, controlled by variations in the geometry of the earth''s orbit. These changes represent the major driving force in the earth climate system through time, including glacial-interglacial cycles. Thirty-six vertebrate fossil localities, including three hominid sites, can be linked directly to this sequence, providing an opportunity to establish patterns of response by animals and vegetation to these short term shifts. This research represents the first attempt to develop multiple environmental and ecological indicators that can be linked directly to Milankovitch cycling in a terrestrial rift valley context. These data will be used to generate insights into the evolutionary response of hominid ecosystems to these pervasive climatic oscillations over the last six million years in Africa. While these data relate directly to fossil hominids and their vertebrate communities in the Baringo Basin, linking local ecological shifts with orbitally-forced patterns of insolation affords the prospect of extrapolating the affects of climatic oscillations on terrestrial ecosystems regionally in the past. With these data, we can begin to formulate high-resolution models for interpreting correlations between climate and human evolution, and elucidate the role of environmental change as a potential driving force in mammalian evolution in general and human evolution in particular. This research will foster highly interdisciplinary and collaborative studies, essential in developing perspectives of the multi-dimensional links between evolution and ecology. The project outlined here represents an ideal forum in which to generate and integrate research ideas cutting across traditionally disparate academic disciplines. The study will broaden opportunities and enable the participation of graduate students as well as research personnel from the National Museums of Kenya.